IN ANIMALS continued
Occurrence, distribution, and abundance of feral pigs throughout Australia. From National Land and Water Resources Audit and Invasive Animals Cooperative Research Centre (2008). Assessing Invasive Animals in Australia 2008, NLWRA, Canberra.
Feral pig (Sus scrofa) Occurrence, Abundance and Distribution
Present – Abundance / Distribution Unknown Occasional / Localised Occasional / Widespread Common / Localised Common / Widespread
Abundant / Localised Abundant / Widespread Absent Unknown
CLINICAL DISEASE • Clinical signs in dogs are referable to the reproductive tract (orchitis, prostatitis, abortion),
• Brucella suis usually infects pigs and is enzootic in the feral pig population in Queensland and northern NSW. The seroprevalence of B. suis in feral pig populations in NSW is estimated at 3%, with cases found only in northern regions. 6 In Queensland seroprevalence in pigs has been reported as 4%. 7 • Brucella suis results in widely disseminated infection in pigs. The organism is found in blood, tissues and urine, with particularly high levels in reproductive tissues/placentae. The most common signs in pigs are reproductive losses (abortion, stillbirths, weak live-born piglets), however these are unlikely to be noticed with the unmanaged husbandry of feral pigs. Orchitis and epididymitis may be seen in boars. Non-pregnant pigs are frequently asymptomatic, although some animals may develop arthritis, discospondylitis, or complications from abscess formation in other tissues and organs. 8 • Organisms may remain viable in moist environments protected from direct light for months. Epidemiological significance of this for transmission to dogs is unclear. Brucellae may survive for years in frozen meat. • Dogs are infected via ingestion, inhalation or exposure to mucous membranes, conjunctiva, or abraded skin following exposure to infected tissue. • Dog-to-dog sexual transmission is considered possible.
axial skeleton (discospondylitis) or appendicular skeleton (lameness), however infection may be subclinical. In one study, 40% of dogs testing positive (rose bengal test) were subclinical, while of the clinical cases 33% dogs exhibited reproductive signs, 13% had back pain and 10% had lameness. 10 • High numbers of organisms are found in reproductive organs and placental tissue and fluids. It is likely that some pig- hunting dogs experience reproductive issues caused by B. suis infection. 11 • Data on the duration of bacteraemia is limited, however as many cases are culture negative, it may be short. Brucella suis has been cultured from the semen of affected dogs. • Affected dogs should be neutered. They may be treated with combination antimicrobial therapy (doxycycline and rifampicin) however the organism may persist in treated dogs and recrudesce, with resultant zoonotic implications. Euthanasia should therefore be considered. 1,10 DIAGNOSIS • In dogs, serology, based on cross reactivity against B. abortus (exotic to Australia), can be used to determine exposure to B. suis. Dogs may be seronegative early in the course of infection, and clinically suspicious cases should be retested 6 weeks later. • Culture from tissue or blood can be used to confirm diagnosis, however many cases are culture negative. • Diagnostic testing is restricted to state government laboratories who are able to perform serology using the rose bengal test, with confirmatory complement fixation testing. Practitioners are advised to contact their respective state government bodies for the latest information on testing suspected cases. • Veterinary staff should wear appropriate PPE when collecting samples from dogs with suspected infections, and laboratory staff should be notified that specimens are potentially infected with Brucella.
PREVALENCE AND RISK FACTORS • For dogs, exposure to feral pigs is the biggest risk factor. This may either be through hunting feral pigs,
through being fed raw meat/offal from feral pigs or through indirect exposure to materials contaminated with bodily fluids or tissues from feral pigs. • Seroprevalence of B. suis in pig hunting dogs has been investigated in a number of studies. The survey adjusted true seroprevalence for B. suis in dogs from pig hunting households across NSW and southern Queensland is 9.4%. In NSW, seropositive dogs were found mainly in the north and central west of the state. (Pers. comm. Cathy Kneipp, PhD scholar). In another study in north Queensland, 1% (1/97) of clinically healthy pig hunting dogs were found to be seropositive on both
compliment fixation and rose bengal testing. 9 • Brucella suis has not been reported in cats.
CONTENTS
21 Companion Animal Zoonoses Guidelines
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