TRANSMISSION
• Strongyloidiasis is transmitted by infective filariform larvae penetrating human skin, usually following contact with moist soil contaminated with faecal matter. 16
IN HUMANS
PREVALENCE AND RISK FACTORS • Strongyloidiasis occurs after larval penetration of intact skin in contact with contaminated soil, and is considered primarily a disease of tropical and subtropical areas. 17 Infection may however occur in any location where poor sanitation or other risk factors are present that enable transmission through environmental faecal contamination. 17,18 • It is estimated that 600 million people globally are infected with Strongyloides . 4 Estimates of strongyloidiasis prevalence within endemic areas in Australia vary widely dependent on diagnostic methodology, study population and seasonality, with reported prevalence rates based on faecal larval detection ranging from 1% (for the majority, living in temperate and urban settings) to 41% (in certain high risk groups). 3 Strongyloides stercoralis prevalence has been demonstrated as high as 60% in remote Aboriginal and Torres Strait Islander communities in northern Australia. 3 Children are documented to have a higher prevalence than adults. 3 In other parts of the world prevalence increases with age, as it is a cumulative life-long infection. • In Australia, strongyloidiasis is most commonly identified in those living in or travelling to Aboriginal communities, immigrants from endemic settings (including tropical and Mediterranean countries), refugees, war veterans (World War II veterans serving in the Asia-Pacific and Vietnam War) and returning travellers from endemic areas. 19 CLINICAL DISEASE • Strongyloides stercoralis may persist indefinitely in the absence of exogenous infection via the process of autoinfection. Eggs laid by female worms in the small intestine hatch to produce rhabditiform larvae which are excreted in the faeces. Some larvae transform in the large intestine into infective filariform (L3) larvae which then penetrate the gut mucosa or perianal skin to undergo pulmonary and tracheal migration and re-develop as adults in the intestines. 18 Hence patients can retain replicating Strongyloides in the gastrointestinal tract for decades after initial exposure. Patients remain largely asymptomatic, unless hyperinfection or disseminated infection is induced, usually after initiation of immunosuppression as part of a disease process or treatment.
• Acute and chronic manifestations of strongyloidiasis are recognised: - In acute strongyloidiasis, a local reaction can occur almost immediately at the site of larval entry. Clinical presentation is related to the path of larval migration from the site of infection. Pulmonary symptoms (cough, tracheal irritation) may occur within a week, and gastrointestinal signs (diarrhoea, constipation, anorexia, abdominal pain) can occur as early as three weeks after infection. 17,18 Larval migration through the bowel wall can carry faecal flora into the bloodstream or peritoneal cavity. Hence the first recognition of strongyloidiasis is sometimes presentation with acute or recurrent gram-negative sepsis. - Chronic strongyloidiasis is often asymptomatic. Symptomatic patients may have intermittent gastrointestinal manifestations such as diarrhoea, constipation and vomiting. Dermatological conditions such as pruritus, urticaria, angioedema and larva currens (a cutaneous eruption that causes a pruritic, serpiginous or linear rash along the lower trunk, thighs and buttocks resulting from migrating larvae through the subcutaneous tissues) are described. Peripheral eosinophilia is frequently noted, even in asymptomatic patients. 18 • The majority of zoonotic Strongyloides infections are asymptomatic and self-limiting, however immunosuppression may be associated with accelerated autoinfection and a subsequent hyperinfective (or disseminated) syndrome which is often fatal. Risk factors for infection include patients with HIV/ AIDS, alcoholism, patients with diarrhoea and malignancy. 16 Children are noted as a higher risk group. Individuals with impaired cell mediated immunity (such as transplant patients, patients receiving corticosteroids or immunosuppressants) are also at risk. 8 • Transmission of S. stercoralis infection has also been suggested by transplantation of organs where only the donors had a historical exposure and the recipient subsequently developed disease. 18 • Faecal microscopy will rarely detect the presence of Strongyloides unless accompanied by culture concentration methods (traditionally ‘Harada culture’, Baermann’s technique
CONTENTS
81 Companion Animal Zoonoses Guidelines
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