Zebra Grant Project Prevalence of Encephalitozoon Cuniculi in a Population of Wild Rabbits in Norfolk, England

Serum samples from 27 wild rabbits (Oryctolagus cuniculus) and two wild brown hares (Lepus europaeus) were tested for the presence of antibodies to Encephalitozoon cuniculi using an indirect enzyme linked immunosorbent assay. Brain and kidney samples from the same animals were also examined for the presence of lesions consistent with encephalitozoonosis. The sample population included in the survey consisted of any rabbits or hares presented to the Royal Society for the Prevention of Cruelty to Animals Wildlife Centre in East Winch, Norfolk, England over a time period of approximately nine months in 2006. All animals included in the survey were those that had to be euthanased due to injury, infection or any other trauma. None of the rabbits or hares sampled showed a positive antibody titre for E. cuniculi at a serum dilution of 1:20. One rabbit showed an equivocal weak positive at a serum dilution of 1:10 where a positive reaction at a dilution of 1:20 is accepted as a true positive. None of the tissues examined had lesions that were consistent with E. cuniculi infection. This result suggests that either E. cuniculi is not present in the wild rabbit population in Norfolk or is present at a prevalence rate of less than 10.5 %. A larger sample size covering different regions of the country would be necessary to assess whether the parasite is present in the wild rabbit population in England. Introduction Encephalitozoon cuniculi is a single-celled, obligate intracellular protozoal parasite of the genus Microsporidia. There are over 1000 species of Microsporidia, which are known to infect all major animal groups. Most species infect invertebrates, but many have been shown to infect mammals and several can infect humans. E. cuniculi is the species most commonly reported to infect mammals and can infect many different hosts including mice, guinea pigs, hamsters, dogs, cats, foxes, mink, monkeys, sheep, goats and humans (Didier, Didier, Snowden & Shadduck 2000, Hollister, Canning & Willcox 1990, Didier, Vossbrinck, Baker, Rogers, Bertucci & Shadduck 1995). The resulting disease appears to be more severe in monkeys and dogs (Percy and Barthold 2001). Several Encephalitozoon species have been recognised as being zoonoses, including E. cuniculi. They have been reported as causing opportunistic infections in immune compromised people, predominantly acquired immune deficiency syndrome (AIDS) patients or organ transplant recipients (Hollister and others 1990). Infection presents as diarrhoea, renal disease and keratoconjuctivitis. They have also recently been documented as causing diarrhoea in healthy individuals including adults travelling abroad and children (Didier and others 2000). Microsporidia are characterised by producing resistant spores. The spores contain a polar filament that pushes through the host cell wall allowing the spore contents to gain entry into the target host cell, where they differentiate and multiply. The host cell eventually ruptures, releasing new spores, which can infect other host cells or be passed into the environment via urine, faeces or respiratory secretions, with infection usually occurring through ingestion or inhalation of spores (Didier, Snowden & Shadduck 1998, Pakes and Gerrity 1994). The main route of infection of E. cuniculi is oral although transplacental transmission and inhalation are also reported (Baneux and Pognan 2003; Cox, Pye, Edmonds & Shepherd 1980, Didier and others 1998). After ingestion, the organism is carried in the blood to target organs, primarily the central nervous system (CNS) and kidneys, however liver, lung, heart and lens may be involved (Percy and Barthold 2001). Eye lesions have been associated with intrauterine infection in rabbits (Harcourt-Brown 2004). The eventual rupture of host cells in these target organs leads to inflammatory reactions with granuloma formation. This results in focal granulomatous meningoencephalomyelitis with astrogliosis and perivascular lymphocytic inflammation in the CNS and granulomatous interstitial nephritis in the kidney (Percy and Barthold 2001). The primary host for E. cuniculi is the rabbit, with antibodies first detectable in rabbit serum about three weeks post infection. Peak titres occur at six to nine weeks after infection. Serum antibodies are detectable at least two weeks before organisms can be demonstrated intracellularly and four weeks before histopathological changes can be found in the kidney. Lesions are not usually identifiable in the brain until eight weeks after antibodies are present in the serum (Cox and Gallichio 1978, Harcourt-Brown 2001). Laboratory kits have been shown to have protective maternal antibodies, which wane after weaning (Bywater and Kellett, 1978, Lyngset, 1980). Spores can be detected in urine samples four weeks after infection and large amounts of spores are excreted until two months post infection drifting to undetectable amounts by three months post infection. Spores can remain viable for at least six weeks at room temperature (Percy and Barthold 2001).