IBR Eradication leaflet series
ANIMAL HEALTH IRELAND Contributing to a profitable and sustainable farming and agri-food sector through improved animal health
IBR in Cattle Frequently Asked Questions
Apparently healthy bulls may actually be latently infected and these are a risk to a naïve herd.
Animal Health Ireland, 2-5 The Archways, Carrick-on-Shannon, Co. Leitrim, N41 WN27 IBR ERADICATION PROGRAMME
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Animal Health Ireland, 2–5 The Archways, Carrick-on-Shannon, Co. Leitrim, N41 WN27 IBR ERADICATION PROGRAMME
IBR in Cattle Frequently Asked Questions
Q1. Q2. Q3. Q4. Q5. Q6. Q7. Q8.
What causes IBR?
How common is IBR in Irish beef and dairy herds? How does IBR affect an individual animal? How should I manage an animal with IBR?
How does IBRV spread?
What are the likely consequences of having IBR infected animals in a herd?
How do I stop IBR from coming into my herd? What tests are available to investigate IBR?
Q9. How do I test a herd for IBR? Q10. How do I decide whether to start a control programme for IBR in a herd? Q11. What different options are available to control IBR in a herd? Q12. What types of vaccines are available against IBR? Q13. How do I decide whether or not to vaccinate a herd for IBR? Q14. What is the risk of introducing IBR with semen purchased from an AI centre? Q15. Can humans be affected by IBR? Q16. Is there a national programme for IBR control in Ireland?
Animal Health Ireland, 2-5 The Archways, Carrick-on-Shannon, Co. Leitrim, N41 WN27 IBR ERADICATION PROGRAMME
Please refer to the disclaimer on the last page regarding information in this leaflet.
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What causes IBR?
A viral disease of cattle ‘IBR’ stands for ‘Infectious Bovine Rhinotracheitis’. The disease spreads between cattle and can cause the nose and upper airways to become inflamed. The disease usually occurs when an animal is first exposed to a herpes virus called ‘Bovine Herpes Virus-1’ (BoHV-1) (Muylkens et al., 2007) and so this virus is also known as IBR virus (IBRV). The severity of disease caused by infection with BoHV-1 can vary from inapparent to very severe (OIE, 2010) . In this document, we will refer to any infection with BoHV-1 as ‘IBR’ even though many infections are not associated with obvious respiratory signs. An animal can therefore be infected with IBR (and test positive for IBR antibodies) even if it has never had the typical signs of disease. See Q3: ‘How does IBR affect an individual animal?’ for more detail on the range of clinical signs that can occur after infection with IBR and the infection cycle in an individual animal. IBR affects cattle trade IBR-infected animals (and any associated products such as semen or embryos) cannot be traded to many regions and countries in the EU that are officially recognised as free of IBR (Denmark, Germany, regions of Italy, Austria, Finland, Sweden) or have an approved IBR control programme (Belgium, Luxembourg, regions of Italy and the Czech Republic) (2004/558/EC and amendments) . From 2021, this legislation will be superseded by REGULATION (EU) 2016/429 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 9th March 2016 on transmissible animal diseases and amending and repealing certain acts in the area of animal health (‘Animal Health Law’) which makes provision for official approval of national and regional IBR eradication programmes within Member States, and provides continued protection for existing or newly recognised programmes. In addition, many third countries have IBR-specific requirements for live exports. Non-EU countries that are IBR free (Norway, Switzerland) also restrict entry of test positive animals, while many third countries have specific IBR-related requirements for live imports. In addition animals that have IBR antibodies following infection or vaccination with ‘Conventional’ (Non-Marker) or ‘Marker’ vaccines cannot enter semen collection centres in Ireland. Bovine Herpes Virus-1 can cause other diseases IBR can also cause a disease of the genital tract called ‘Infectious Pustular Vulvovaginitis’ (IPV; cows) or ‘Infectious Pustular Balanoposthitis’ (IPB; bulls) (Muylkens et al., 2007). At present, these diseases are not seen commonly in Ireland and abortion in pregnant females and pharyngitis (inflammation of the throat) in calves following infection with IBR occurs occasionally.
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Bovine Herpes Virus-1 sub-types and strains BoHV-1 Sub-types
There are three recognised sub-types of BoHV-1, based on DNA analysis (Muylkens et al., 2007) . Viruses belonging to different sub-types tend to be associated with particular disease outcomes, although the distinctions are not absolute.
• BoHV-1.1: Mainly causes IBR and can also cause abortion. • BoHV-1.2a : Mainly causes IPV/IPB and can also cause abortion. • BoHV-1.2b: Mainly causes IPV/IPB but does not cause abortion. BoHV-1.1 Strains
There are different strains of virus within each sub-type. This is important as differences between strains may affect the severity of the disease they cause in an animal. In an experiment where young calves were exposed to different strains of BoHV-1.1 some strains caused severe disease and death where as others caused much milder disease (Kaashoek et al., 1996) . Strain differences may account for some of the wide range of clinical signs that are reported from natural cases of infection with BoHV-1. There is no published evidence of any mismatch between the Irish field strains of IBR and those vaccines currently available on the Irish market. See Q3: ‘How does IBR affect an individual animal?’ for more detail on the range in clinical signs that can occur with IBR. Despite these differences, all sub-types and strains of BoHV-1 are considered to belong to the same viral species. NOTE: When an animal is infected with any of these sub-types/strains it is considered to be infected with IBR virus. See Q8 ‘What tests are available to investigate IBR?’ for more details on testing an animal. Other herpes viruses of cattle There are other herpes viruses that affect cattle and cause diseases that are very different to those caused by IBR (Banks et al., 2008; Muylkens et al., 2007) . For example: • BoHV-2 causes Herpes Mammillitis (producing teat ulcers). • BoHV-4 has an undefined role but may contribute to reproductive disorders and mastitis. • BoHV-5 causes herpes encephalitis (producing nervous signs). • Ovine Herpes Virus-2 (a herpes virus of sheep) occasionally causes severe disease in individual cattle called ‘Malignant Catarrhal Fever’. • BLHV, (Bovine Lymphotrophic Herpesvirus) like OHV-2 above is a gamma-herpesvirus and has been linked with chronic, non-responsive metritis in dairy cows. These other viruses are considered as separate species and not generally part of IBR disease syndrome.
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Q 2 How common is IBR in Irish beef and dairy herds?
IBR infection is very common Infection with IBRV (the virus that causes IBR) is very common in Irish beef and dairy herds. Consistent with other countries that do not have a control programme, it is estimated that between 70% and 80% of all Irish herds contain at least one animal infected with IBR i.e. 70–80% of herds are ‘infected herds ’ (Cowley et al., 2011). There is no marked difference in prevalence between beef and dairy herds and both are very likely to be infected (Cowley et al., 2011). Proportion of infected cattle varies between herds The proportion of infected individual animals can vary widely between different infected herds. Some infected herds may have only a single infected animal. More commonly, many animals are infected, and in some cases all animals can be infected (Geraghty et al., 2012; O’Grady et al., 2008). Prevalence in suckler and dairy herds has been shown to increase with parity, herd size and purchasing (Barrett et al. 2018). As IBR may not circulate continuously in infected herds, the length of time since the last virus circulation may be an important factor in explaining this variation (Geraghty et al., 2012; van Nieuwstadt and Verhoeff, 1983) . The structure and management of the herd may also influence the number of animals that are infected with the virus and the age at which infection occurs.
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How does IBR affect an individual animal? Q3
The course of infection in an individual animal Figure 1 highlights the steps that an infection with IBRV (the virus that causes IBR) has in animals.
The animal has never been exposed to IBRV.
The first time an animal is infected by the virus is called the primary infection. This is the only step commonly accompanied by clinical signs, but these can vary from very mild to severe. The infected animal sheds a lot of virus that can infect other animals. The animal mounts an immune response and antibodies are readily detectable after approximately three weeks. Infected animals are the most important source of infection for their comrades.
After recovery from primary infection the virus survives within the nerves of the infected animal without causing any clinical signs. The animal is now a carrier but does not shed the virus. This is called a latent infection. Latently infected carrier animals are almost always detectable by antibody testing.
STRESS CAN CAUSE REACTIVATION
During periods of stress, the virus can reactivate within a latently infected animal, causing a secondary infection that usually has no clinical signs. Virus is shed again and can spread to other animals, potentially starting new primary infections in naïve animals. Secondary infection also occurs when a latently infected carrier animal is re-exposed to circulating virus.
REACTIVATION AND SECONDARY INFECTION
Figure 1. Infection cycle of IBR in an individual animal.
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Only the primary infection is commonly associated with any clinical signs, although clinical signs may vary from minimal to severe, and in some cases may be absent. Latent infection refers to a carrier state where the virus survives in an infected animal (though not causing disease or spreading). All animals that have had a primary infection should be considered to be latently infected. Reactivation of latent infections provides a source of virus to create new primary infections in naïve (previously unexposed) cattle in the herd (Muylkens et al., 2007) . Secondary IBR infections (either after reactivation or from circulating virus) usually produce minimal or no clinical signs. Primary infection IBRV typically infects an animal through the nose or mouth following direct contact with an animal shedding the virus (Muylkens et al., 2007) . The virus may also travel short distances (3–5m) in air (Mars et al., 2000) . Transmission at breeding (natural or artificial) and through indirect contact with infected animals is also possible. Following primary respiratory infection, the virus damages the surface of the nose and the upper airways and may enter the blood to spread to other parts of the body. NOTE: Some primary infections produce no apparent clinical signs while others can be very severe. (EFSA, 2006; Muylkens et al., 2007) . The following clinical signs may be caused by (but are not unique to) IBRV infections: • Dullness and reduced appetite. • High body temperature. • Rapid and loud breathing sometimes with coughing. • Inflammation inside the nose and in the pink of the eye (conjunctiva) or less commonly on lining of male or female reproductive tracts. • Fluid discharge from nose and eyes. • Pharyngitis (inflammation of the throat). • Sudden reduced milk production. • Abortion. • Nervous signs (only in young calves). In addition, IBR can lead to marked respiratory disease and in severe cases death or long term ill-health. Remember that cattle with these signs are not definitely affected with IBR; it is important to discuss any suspect animal with your own veterinary practitioner. Occasionally, young calves can also show severe nervous signs as the virus invades the brain (Muylkens et al., 2007) . These clinical signs are only seen in some cases. Many primary infections are inapparent. Factors that may influence whether clinical signs are seen during an outbreak include: • The ability of the animals to fight infection. • Concurrent infections. • Whether animals have been vaccinated against IBR. • The level of immunity (including colostral immunity in calves). • The strain of the bohv-1 virus. (EFSA, 2006; Muylkens et al., 2007) Evenwithin a single IBR outbreak, different animals can showdifferent clinical signs due to individual animal differences in these types of factors. See Q1: ‘What causes IBR?’ for more detail on the different strains of BoHV-1.
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Latent infection NOTE: All animals that have a primary infection subsequently develop a latent infection.
During the primary respiratory infection the virus enters the nerves of the head. After recovery from the clinical signs, the virus is able to survive for the lifetime of the animal in these nerves. The virus is said to be in a ‘latent’ state (Muylkens et al., 2007) . This means that all animals that have ever been infected with IBRV are considered to be lifelong carriers. However, as the virus is ‘latent’ (i.e. not replicating or causing disease) the animal shows no ill effects and does not spread virus to other animals until reactivation occurs (see below). In almost every case, animals with latent infection will have antibodies against IBR that can be detected in blood and milk (Muylkens et al., 2007) . By testing for antibodies we can identify animals that are latently infected carriers. NOTE: In very rare cases an animal can be latently infected but have no detectable antibodies, and therefore cannot be identified by a serological laboratory test. These are called ‘sero-negative latent carriers’. See Q8 ‘What tests are available to investigate IBR?’ for more details on testing for latent infection. Reactivation and secondary infection IBRV within latently infected animals can re-activate to start a secondary infection and may spread to other, naïve animals. Secondary infections are almost never accompanied by any clinical signs because the animal already has some immunity from the primary infection (Muylkens et al., 2007) . Secondary infections (with no clinical signs) can also occur when a previously infected animal comes into contact with circulating virus (i.e. without reactivation). Over its lifetime, reactivation may occur multiple times within the same animal, interspersed with periods of latency. NOTE: Reactivation is very important because it allows virus to be spread to uninfected animals in an infected herd or introduced to uninfected herds. Virus may spread between herds when latently infected animals are introduced. If the virus contacts an uninfected animal a new primary infection will take place, with the risk of clinical signs developing. The level and duration of virus shedding is greater during primary infection than during secondary infection. Reactivation may occur when an animal is under stress. Transport, calving, and high doses of immuno-suppressive drugs (e.g. corticosteroids) have all been shown to stimulate reactivation (Thiry et al., 1987; Thiry et al., 1985) . Other stressful events such as lameness, nutritional stress, mixing stock and other diseases are also likely to stimulate reactivation of latent infection.
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How should I manage an animal with IBR? Q4
Treating clinical infections As the treatment required varies with the cause of the problem, veterinary examination of suspected cases is essential. Therefore, if you have an animal that is showing signs consistent with IBR, a veterinary practitioner should be called to examine the animal, confirm the diagnosis and discuss treatment. There are several other diseases that cause similar signs, including lungworm, bacterial and other viral pneumonia, mycoplasma bovis and sunburn (Radostits et al., 2007) . Less common diseases like malignant catarrhal fever and some exotic diseases such as foot and mouth disease can also cause similar signs. Specific treatment of the sick animal will vary on a case-by-case basis. If a diagnosis of IBR is made, the veterinary practitionermay advise immediate isolation and vaccination of the sick and ‘at-risk’ animals with intranasal vaccination to reduce clinical signs and control spread of infection. NOTE: If animals are to enter a semen collection centre or bull testing station in the Republic of Ireland they must not be vaccinated with any type of vaccine (including ‘Marker’ vaccines). See Q3: ‘How does IBR affect an individual animal?’ for more detail on the range of clinical signs that can occur after infection with IBR. See Q13: ‘How do I decide whether to vaccinate a herd for IBR?’ for more detail on vaccination. Treating latently infected animals There is no treatment (or vaccination) that can remove latent infection from an animal (Muylkens et al., 2007) . However, regular vaccination of latently infected animals can help to reduce reactivation and transmission to other cattle. See Q13: ‘How do I decide whether to vaccinate a herd for IBR?’ for more detail on vaccination. IBRV infection does not cause any clinical signs when in a latent state (Muylkens et al., 2007) . If an animal is showing signs of ill-health it is unlikely to be due directly to latent infection and veterinary examination is required. See Q3: ‘How does IBR affect an individual animal?’ for more detail on primary and latent infections with IBR.
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How does IBR spread? Q5
IBR spread on a farm Direct contact (e.g. nose to nose) is the most important method by which IBRV is transmitted from an animal that is shedding the virus to a susceptible animal (Muylkens et al., 2007) . The virus can also spread between animals over short distances in air (3–5m) e.g. between animals grouped in pens or across boundaries (Mars et al., 2000) . The virus is highly contagious and it has been estimated that single animals shedding IBR can infect as many as seven more susceptible in-contact animals (Hage et al., 1996) . Newborn calves in very close contact with their previously infected dams are a particular risk group. Virus Shedding Virus can be shed during primary and secondary infections and following reactivation. The main routes of shedding are: • In fluid from the nose, eyes and mouth. • In the semen of bulls.
• In fluids from the female reproductive tract. (Dennett et al., 1976; Muylkens et al., 2007)
Unlike other pathogens, IBRV transmission is not thought to commonly occur via milk or faeces. Latently infected animals do not continuously shed virus (Muylkens et al., 2007). The latent virus must first reactivate (usually following a period of stress or immune suppression) and then shedding may occur for a limited period of time (around 10–20 days) (Muylkens et al., 2007) . Any other animals that undergo a primary infection as a result during this time may get sick. These animals will shed more virus (than latently infected animals do after re-activation). This cycle allows IBRV to survive in a herd for a long time.
‘Apparently’ healthy latently infected carriers (antibody test positive)
Newly infected animals
Figure 2a. Spread of IBRV following reactivation and shedding of virus from carrier animals.
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If sold: Carrier animal introduced to new herd with risk of outbreak
If calves kept as replacements, maintains infection in the herd, becoming source of infection for future generations
Recovered animals become latently infected carriers
Infection spreads between other naïve animals
Reactivation of virus in cows leads to infection spread
Calves managed with cows until weaning
Infected herd with latently infected cows
‘Apparently’ healthy latently infected carriers (antibody test positive)
Newly infected animals
Figure 2b. Spread of BoHV-1 (IBR) in a non-vaccinating suckler herd following reactivation from carrier animals.
Indirect contact (the movement of infectious fluids on contaminated clothing, hands, feed or equipment) between animals may also allow virus to spread on a farm. The virus may also transfer indirectly between animals sharing feeding, drinking or bedding and can survive for several days off the animal. See Q3: ‘How does IBR affect an individual animal?’ for more detail on primary and latent infections with IBR. See Q11: ‘What different options are available to control IBR in a herd?’ for information on reducing the source and spread of virus on your farm.
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IBR spread between herds There are several routes that allow IBR to spread between herds. See Q7 ‘How do I stop IBR from coming into my herd?’ for information on reducing spread between herds. Spread by introducing stock The introduction of latently infected animals (that are carriers but have no signs of disease) is the most common way for IBRV to spread between herds. Any animal that has ever had a primary infection should be considered to be latently infected. In Ireland, because of the high prevalence of IBRV in the national herd, purchased animals should
be considered as latently infected unless proven otherwise. Animals are brought into herds for different reasons such as: • Stock bulls. • Replacements for culled animals in a beef or dairy herd. • Genetic improvement and associated embryo recipients. • Dairy heifers returning from a rearing centre. • Fattening in a beef unit. • Herd expansion.
These are all potentially high risk activities for introducing IBRV into a herd. The stress of transport and mixing may re-activate latent IBRV infection and cause an outbreak of disease soon after animals have been introduced. Spread by close contact between animals Close contact with cattle from other herds is the next most common method for IBVR to spread between between herds (EFSA, 2006). Activities that allow direct or close contact (3–5m) between animals from different herds include: • Inadequate perimeter fencing. • Mixing stock for husbandry activities, at pasture, agricultural shows, marts or during transport. • Animals breaking into/out of farms (and mixing with a neighbour’s stock). Spread by indirect contact (fomite spread) Infected fluids (e.g. nasal discharge) that contaminate hands, clothing, farm equipment (nose-tongs, crush etc), feed or vehicles can spread IBRV between herds (EFSA , 2006; van Schaik et al., 2001b). Farm visitors that have close contact with stock may transfer the virus if they do not change or clean and disinfect their outer clothing and wash hands when moving between herds (van Schaik et al., 2001b) . Farm staff that contact stock in other herds pose a similar risk. Spread by semen Semen from infectious bulls can transmit IBRV between herds. However, the risk from semen obtained from collection centres approved for intra-community trade in the EU (2003/43/EC) , where bulls must be free from IBR, is negligible (EFSA, 2006) . NOTE: All semen collection centres in the Republic of Ireland (ROI) must be approved for intra-community trade and therefore they present negligible risk of spreading IBR. In some other EU countries, IBR infected bulls may enter semen collection centres provided that they are not approved for intra-community trade and semen collected is only used on the domestic market under these circumstances. The risk of IBRV being present in semen from such collection centres is therefore increased (EFSA, 2006). NOTE: It is illegal to import semen from non-approved IBR-permissive centres in other EU countries into ROI.
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Spread by embryo transfer Embryos can be contaminated with IBRV and therefore potentially spread virus between herds. The risk is generally low and depends on the exact methods that are used. The following practices reduce the risk of spreading IBRV by embryo transfer: • Ensuring any purchased recipients are IBR-free. • Sourcing semen from eu approved collection centres: See above (2003/43/ec) (si112 1996) . • Sourcing ibr free donors and recipients. • Washing embryos in trypsin (required by internationally approved processing protocols). • Using IBR free donors of somatic cells and foetal calf serum. (Givens and Marley, 2008) See Q8 ‘What tests are available to investigate IBR?’ for more information on ensuring animals are free from IBR infection. When ‘in-vivo’ embryos are used (i.e. the egg is fertilised in a cow rather than in a laboratory) and the embryo is washed in trypsin as required by internationally approved protocols, the risk of transfer of IBRV is believed to be
negligible (Givens and Marley, 2008) . Spread by milk and faeces
IBRV can be shed in both milk and faeces from animals during primary and secondary infections and after re-activation of latent infections. While spread via milk has been shown to occur experimentally, spread of infection via slurry has never been documented (EFSA, 2006; Probst et al., 1985) . Movement of milk and faeces are not thought to be common methods of spreading IBRV between herds (ESFA, 2006) . Spread by other species Sheep, goats and deer can all be infected by IBRV and may present a small risk of spread between herds (Mollema et al., 2005; Thiry et al., 2006) . Spread by insects or rodents Transfer from from insects or rodents has never been documented and it is unlikely to be a common or significant method of spread of IBRV between herds (EFSA, 2006; Taylor et al., 1982) .
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What are the likely consequences of having IBR infected animals in a herd?
Herd infections with IBR IBR virus can affect a herd when it is first introduced or by circulating in a herd that is already infected. Most (but not all) herds in Ireland already have latently infected animals (Cowley et al., 2011) . The following describes possible outcomes that may that occur following both new infections and circulation of virus in infected herds. Clinical impact of IBR can vary IBRV can have variable clinical consequences ranging from being inapparent through to very severe in individual animals (Pritchard et al., 2003; Wiseman et al., 1978) . This means that, at the herd level, the negative effects may also vary from slight to more severe. What causes these differences is not fully understood (EFSA, 2006; Muylkens et al., 2007) . Factors that may influence the consequences of having IBR in a herd are: • The ability of the animals to fight infection and and ongoing causes of stress.
• Whether animals have been vaccinated against IBR. • Concurrent infections- vira l, bacterial, parasitic. • The level of immunity (including colostral immunity in calves). • The strain of the BoHV-1 virus.
Even within a single IBR outbreak, different animals can show different clinical signs due to individual animal differences in these types of factors. While both the BoHV-1.1 and BoHV-1.2 subtypes have been identified in Ireland, their relative prevalence in Irish herds is unknown. See Q1: ‘What causes IBR?’ for more detail on the different strains of BoHV-1. Herds with clinical cases In some herd infections with IBRV the clinical impact is severe (VLA, 2011; Wiseman et al., 1978; Wiseman et al., 1979) . The virus can reduce the health and production of cows and calves (Miller and Van der Maaten, 1986; Muylkens et al., 2007) . The following consequences are associated with primary infections: • Reduced animal welfare. • Reduced appetite and growth rate/milk yield. • Increased risk of pharyngitis and secondary bacterial pneumonia. • Risk of abortion. • Risk of death. Some studies suggest that feedlot enterprises are more likely to suffer severe outbreaks than dairy or suckler herds (Wiseman et al., 1978) .
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Purchasing for store, finishing or export markets IBR is a recognised part of the ‘respiratory disease complex’ in herds where animals are purchased from multiple sources and mixed after purchase. Animals from multiple sources are often of unknown health status and have varying levels of immunity. Transport and mixing of cattle of unknown health status can result in clinical IBR disease (and other diseases) occurring within the group. Mixed infections with other disease causing viruses and bacteria (e.g. BVD) can result in more severe clinical IBR problems. Reduction of stress prior to and during transportation and after arrival on-farm can help minimise the problem. Use of IBR vaccines (ideally in advance of movement or on arrival on farm) can help control the contribution of IBR to the respiratory disease complex. Follow the manufacturers’ recommendations for vaccine use. See AHI CalfCare leaflet on the Management of the Suckler Calf at Weaning to Prevent Pneumonia . In addition, these IBRV infected animals (and their associated products such as semen) cannot be traded to many regions and countries in the EU under current EU legislation (2004/558/EC as ammended and 2003/43/EC) . One of the drivers of national IBRV eradication policies within Europe, in addition to addressing the direct costs associated with the disease is to overcome trade restrictions. Herds with no clinical cases In some herds the clinical impact of infection with IBRV is much less severe. Clinical signs of IBR may not be observed in affected animals and a reduction in milk yield may not be consistently reported (Geraghty et al., 2012; Hage et al., 1998; Pritchard, 1998; Pritchard et al., 2003; van Schaik et al., 2001a) . These ‘sub-clinical’ herd infections are common in endemically infected areas like Ireland (Muylkens et al., 2007) . The direct impact that IBRV is having in such herds is likely to vary between herds and is very difficult to assess. Specific herd goals Animals that are either naturally infected with IBRV or that are vaccinated against IBR can never be taken into semen collection centres or bull testing stations in Ireland (SI 112/1996 as amended) . IBR-infected animals (and any associated products such as semen or embryos) cannot be traded to many regions and countries in the EU that are officially recognised as free of IBR (Denmark, Germany, regions of Italy, Austria, Finland, Sweden) or have an approved IBR control programme (Belgium, Luxembourg, regions of Italy and the Czech Republic) (2004/558/EC and amendments ). Non-EU countries that are IBR free (Norway, Switzerland) also restrict entry of test positive animals, while many third countries have specific IBR-related requirements for live imports. When it is a specific goal of a herd to sell animals into semen collection centres, bull testing stations or to export them to restricted areas then the potential cost of having IBRV, even if the infection has no observed clinical impact, can be substantial. At the national level, IBRV represents an ongoing risk to semen collection centres. It also puts a significant restriction on the number of animals that are eligible for entry into semen collection centres and as a consequence reduces the pool of genetic material available for selective breeding. Many international agricultural shows impose restrictions and enforce specific regulations against IBR.
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How do I stop IBRV from coming into my herd? Q7
Make a bio-exclusion plan Bio-exclusion means preventing infectious disease coming into your herd from outside. The risk of IBRV coming into your herd can be controlled by implementing a bio-exclusion plan in conjunction with your own veterinary practitioner. Farmers are encouraged to find out the IBR status of their own herd as a starting point of any biosecurity plan. To make a plan, any activities that might allow IBRV to enter your herd should be considered, and control measures put in place for each one. It is appropriate to prioritise the control of higher risk activities before addressing moderate and lower risk activities. It may be helpful to read Q5: ‘How does IBR spread?’ before reading this section and making a bio-exclusion plan for your own herd. Further information can be obtained from the bio-security section of the Animal Health Ireland website click here . Activities that may allow IBR to enter a herd Higher risk activities Introducing stock is the highest risk activity for allowing IBRV to enter a herd. Activities that allow direct or close contact between your own animals and animals from outside your herd are also higher risk. For example: • Mixing stock at housing, pasture, during transport, agricultural shows or marts. • Borrowing, loaning, other farms’ bulls. • Having poor perimeter fencing. • Having animals break into/out of your farm and mix with other stock. These are HIGHER risk activities and should be addressed first (EFSA, 2006) . The list is not comprehensive and any activity that allows direct or close contact with cattle from another herd should be considered HIGHER risk. Moderate risk activities Activities that allow ‘indirect contact’ between your herd and animals from outside your herd can also allow IBRV to enter your herd (EFSA, 2006; van Schaik et al., 2001b) . ‘Indirect contact’ occurs when animal secretions and excretions (nasal discharge, saliva, urine, dung etc) are moved between farms by a carrier. For example: • Visitors with contaminated clothing moving between herds. • Using contaminated farm equipment from another herd (e.g. nose tongs, crush etc). • Allowing contaminated vehicles from another herd to contact your stock. These are MODERATE risk activities and should be addressed next. The list is not comprehensive and any activity that allows indirect contact between herds should be considered as a MODERATE risk. Lower risk activities Lower risk activities are those which can in theory allow IBRV to spread but are not thought to occur commonly, such as embryo transfer and co-grazing with other ruminants (EFSA, 2006; Givens and Marley, 2008) . They should be considered only after HIGHER and MODERATE risk activities have been addressed. Bio-exclusion control options For each risk activity identified, there can be several different options to help control them. Table 1 indicates, for common activities that may introduce IBR, various control options and how effective they are likely to be.
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How effective will it be?
Higher Risk Activities
Keep a closed herd (including no borrowing or purchasing of bulls) Isolate any incoming stock for four weeks before testing for antibodies; only introduce test-negative animals 1 Introduce stock only from IBR accredited free herds (and isolate for four weeks) Buy stock from herds with no clinical signs of IBR and (and isolate for four weeks after arrival)
Purchasing and introduction of stock
Mixing home stock with cattle from another farm at pasture, housing or by contract rearing
Do not allow home stock to mix with animals from any other farm
Do not graze boundary fields when there are neighbours’ cattle in the adjacent field Ensure all perimeter fencing is unbroken and maintains 5m between stock on a neighbours’ farm
Grazing stock in boundary fields with poor perimeter fencing
Do not take stock to marts and allow them back home
Taking stock to a mart
Take stock to marts but do not allow them back home without isolating and testing
Do not take stock to agricultural shows
Only take stock to shows that require a negative IBR test result for all entrants; if no such shows exist encourage development of these through breed societies; isolate and test (as above) on return from the show Ensure all farm staff change outer clothing and wash hands before and after contact with any external stock Ensure all farm staff disinfect all outer clothing and wash hands before and after contact with any external stock
Taking stock to an agricultural show
Farm staff contacting external stock (e.g. at shows, farm walks etc)
How effective will it be?
Moderate Risk Activities
Provide visitors with clean, disinfected 3 (or disposable) outer clothing (that stays on the farm) and hand washing facilities before they contact stock Ensure visitors 2 completely clean and disinfect 3 all outer clothing and footware before they contact stock
Allowing visitors that move between farms access to stock 2
Do not share farm equipment with a neighbour
Sharing farm equipment with a neighbour (e.g. nose tongs, foot-paring crushes etc)
Do not allow visiting vehicles close contact with stock Ensure vehicles drive through a disinfectant 3 bath before close contact with stock Only purchase semen from collection centres approved to EU standard 2003/43/EC 4 Clean and disinfect 3 all shared farm equipment before and after every use
Visitor’s vehicles coming close to stock 2
How effective will it be?
Lower Risk Activities
Only use in-vivo embryos (produced directly from live animals) that are processed according to guidelines from the International Embryo Transfer Society
Conducting Embryo Transfer 5
Shared grazing with sheep, goats or deer
Do not share grazing with sheep, goats or deer
1 If introducing stock follow the Bioexclusion document guidelines, and see www.animalhealthireland.ie for more information on testing animals. 2 This includes delivery/pick-up drivers and their helpers. 3 A list of approved disinfectants is available from the websites of DAFM (www.agriculture.gov.ie) and DAERA (https:// www.daera-ni.gov.uk/publications/approved-disinfectants ). 4 All semen collection centres in the Republic of Ireland and all legally imported semen must meet these standards. 5 This does not include the risk of purchasing recipients, which is a ‘higher risk’ activity (considered above). Table 1 . Bio-exclsuion control options for activities that present high, moderate and low risks of introducing IBRV into a herd
IBR in Cattle: Frequently Asked Questions | Page 19
What tests are available to investigate IBR? Q8
Test types There are two types of individual animal tests for IBR. • Tests that detect virus directly. • Tests that detect antibody against the virus.
It is important to note that no biological test is 100% accurate and decisions should be made on which tests to use and how many animals to test after careful discussion between the farmer and their own veterinary practitioner based on herd specific goals. Tests to detect virus Tests for the virus (BoHV-1) are usually performed on swabs taken from the nose, eye and throat of an animal (either live or post mortem). There are several different tests that can be used including virus isolation, FAT, antigen ELISA and PCR (EFSA, 2006) and tests for virus are normally used only to confirm IBR infection in an animal with clinical signs. They can all be interpreted as follows: A positive virus test result indicates that the animal was shedding virus when the swab was taken, and was therefore undergoing primary, secondary or reactivation of infection. Following primary infections animals will shed virus for around 10 to 20 days before becoming latently infected (Muylkens et al., 2007) . Animals may also shed virus for a similar period after intranasal vaccination with live IBR vaccine. See Q12 ‘What types of vaccines are available against IBR?’ for more information. A negative virus test result indicates that the animal was not shedding detectable levels of virus when the swab was taken. It may or may not be latently infected. See Q3 ‘How does IBR affect an individual animal?’ for more information on primary, secondary and latent infections. Tests to detect antibody Antibodies are proteins produced by an animal’s immune system and which reach detectable levels (test positive) 10- 35 days after natural infection or vaccination. Antibody tests are performed either on blood or milk, most commonly using an ELISA test. There are two categories of ELISA antibody tests for IBR (EFSA, 2006) . Whole virus or gB tests detect antibodies following natural infection or use of ‘Conventional’ (Non-Marker) or ‘Marker‘ vaccines. or a gE test detects antibodies following natural infection or use of ‘Conventional’ (Non-Marker) vaccination. Tests for antibodies may be used to determine whether an animal has been previously exposed to IBR (and can be presumed to be latently infected) or not. This information can be used in pre-purchase testing and screening ormonitoring herd infection status. See Q9 ‘How do I test a herd for IBR?’ for more information on testing a herd for IBR. Interpreting an antibody test in an individual animal requires knowledge of the type of test used and the vaccinal status of the animal. Table 2 can be used as a guide for interpreting individual animal antibody test results. Calves less than six months old may have maternal antibodies resulting in positive test results. Choosing the right test for IBR NOTE: Remember to use a gE-specific ELISA test in herds that are vaccinating with IBR ‘Marker’ vaccine. ‘Marker’ vaccines, ‘Non-Marker’ (‘Conventional’ (Non-Marker)) vaccines and field virus all cause production of antibodies to the glycoprotein B (gB) of IBR virus. ‘Marker’ vaccines do not contain glycoprotein E (gE) and therefore do not cause production of antibodies to gE. Field IBR virus and ‘Non-Marker’ (‘Conventional’ (Non- Marker)) vaccines do contain gE and therefore lead to production of antibodies to gE. Veterinary Technical Box
IBR in Cattle: Frequently Asked Questions | Page 20
Detectable antibodies to gB/ whole virus
Detectable antibodies to gE
Most likely test results
Previous exposure to IBR virus (regardless of vaccination) OR vaccination with ‘Non- Marker’ vaccine (regardless of exposure) Unexposed but vaccinated with ‘Marker’ vaccine Unexposed and unvaccinated animal
gB or whole virus positive, gE positive
gB or whole virus positive, gE negative gB or whole virus negative, gE negative
Table 2. Influence of animal status and test methods on test results.
In the Republic of Ireland, the only licensed vaccines are ‘Marker’ vaccines. The companion tests are called gE- specific because they detect antibodies to only a small part of the virus (the gE protein). This protein is missing from the ‘Marker’ vaccine but present in the virus strains responsible for natural infection and in ‘Conventional’ (Non-Marker) vaccines (EFSA, 2006) . See Q12 ‘What types of vaccines are available against IBR? for more detail on vaccination. Antibody Test Reliability No laboratory test is perfect and all can very occasionally give an ‘incorrect’ result. In general, test for IBR antibodies are very reliable and very rarely give misleading results. The ‘Marker’ vaccine companion test (gE) is a little less reliable (Kramps et al., 2004) . In addition, there is a longer delay between infection and becoming test positive for the ‘Marker’ test (21-35 days) compared to the gB and whole virus tests (7-14 days) (OIE, 2016) . A test’s ‘Specificity’ score (0-100%) indicates how often the test will give a negative result when testing non-infected animals. A test’s ‘Sensitivity’ score (0-100%) indicates how often the test will give a positive result when testing infected animals. Table 3 gives approximated figures of test reliability for IBR tests (based on data supplied by test kit manufacturers and published reviews ). The best possible test would have 100% sensitivity and specificity. These figures are current as at the date of publication and will be updated as more information becomes available.
99 Specificity Marker vaccine companion test 95 Sensitivity
Individual animal blood sample Sample Type Individual animal milk sample
Table 3. Estimated specificity and sensitivity of selected IBR antibody tests
*Figures shown assumed for both indirect ELISAs and gB specific blocking ELISAs
False negative results occur more frequently as test sensitivity gets lower. False negatives can undermine bio- exclusion efforts if pre- or post-purchase testing is used as part of a bio-exclusion plan. False positive results occur more frequently as test specificity gets lower. False positives can undermine monitoring of herds for evidence of freedom from infection.
IBR in Cattle: Frequently Asked Questions | Page 21
How do I test a herd for IBR? Q9
Conducting a herd test A herd test can be done by combining individual samples or test results to reach a conclusion regarding the status of the entire herd (Christensen and Gardner, 2000) . Herd tests for IBR typically use antibody based tests. Single samples from individual animals are of limited value to determine herd prevalence (the proportion of the herd with IBR). Figure 3 indicates the various stages where herd tests can be used: • To assess IBR status. • To control programme planning. • To control programme monitoring. • To investigate suspect IBR problems. NOTE: All samples from individual animals should be submitted with full tag numbers to ensure the future usefulness of test results to herd health planning. Bulk milk antibody tests A bulk milk antibody test (BMT) can be used as an initial screening test for a dairy herd. This is shown in Figure 3 as a step 1 investigation test. Regular BMT antibody tests may be used in negative/low prevalence dairy herds to monitor their status. Negative bulk milk results with current kits will be obtained in herds where less than 10-15% of the milking cows are latently infected and there is little or no virus circulation. Antibody levels in the bulk milk will increase if the virus starts spreading within the milking herd. A positive bulk tank milk result will be obtained in herds with moderate to high prevalence of latently infected animals, recent circulation of the virus or herds that have been vaccinated (depending on the type of vaccine and test used) (Nylin et al., 2000; Wellenberg et al., 1998) . Individual animal samples are
needed to more accurately determine how many animals are infected. See Q8 ‘What tests are available to investigate IBR?’ for more details.
IBR in Cattle: Frequently Asked Questions | Page 22
Testing a proportion of the herd Accurately estimating how many animals are latently infected is helpful in deciding what sort of control programme is most appropriate for a herd and in determining the next steps. This is shown in Figure 3 (page 26) as a step 2 investigation test. How many animals should I test? Two options are explored in this document: carry out a ‘snap shot’ test or test a proportion of the herd. Snap shot test A cost-effective means to obtain an initial indication of the level of infection in a given herd can be achieved by applying a ‘snap shot’ test. This can be used to get an initial indication of the within herd prevalence and in particular to determine if this is sufficiently low to justify the expense of a whole herd test to confirm freedom or identify the small proportion of positive animals present that require removal. A ‘snap shot’ requires the sampling of 30 randomly selected animals over 9 months-old that are used or intended for breeding. It is important to include animals of all ages and groups in this testing to obtain a result that truly reflects the status of the herd (or that part of it being assessed). Which animals should I test? The animals selected to be tested should be chosen at random (e.g. not targeting sick animals etc.) and should be selected representatively from the groups used to calculate herd size (e.g. all animals or adults only). Calves less than 9 months-old may have maternal antibody resulting in a positive test result. How do I use the result? If either none or only one animal is positive on the ‘snap shot’ test, the proportion of infected animals within the herd (within herd prevalence) is estimated to be between 0-15%. At this low prevalence, screening of the whole herd, to identify and remove any carriers present, is justified where herd freedom is the target. If more than two seropositive animals are identified by the ‘snap shot’ test, the likely within herd prevalence is greater than 15%. In such herds, identification and removal of all carriers is unlikely to be feasible, and therefore other control measures are required until such times as a subsequent ‘snap shot’ test indicates that sufficient progress has beenmade. More detailed testing to determine within herd prevalence To more accurately investigate within herd prevalence e.g. following a positive ‘snap shot’ test or a bulk tank milk result, carry out testing as described below. The number of samples required is influenced by the herd size, the type of sample (e.g. blood or milk) and test (gB or gE ELISA), the desired accuracy of the estimate generated and the
confidence associated with the estimate. How many animals should I test?
Table 4 gives appropriate sample sizes required for estimating prevalence of infection in a herd to an accuracy of +/-5% in 95% of cases (i.e. a confidence of 95%; true prevalence will be within 5% of the estimate 95% of the time).
<25 25-35 36-50 51-75 76-125
>176 ≥275 ≥375 ≥475 ≥575
Whole virus/gB Blood 21
29 29 28 29
38 38 36 38
50 50 47 50
68 67 63 67
81 79 73 79
97 95 86 95
97 95 86 95
118 115 102 115
21 21 21
Whole virus/gB Milk
If you want to know the prevalence in the adults of the herd, only the adults should be included in the herd size figure when selecting your sample size. If you want to know the prevalence in the entire herd all animals should be counted in the herd size. Table 4. Sample size for IBR seroprevalence estimation in herds of various sizes
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