6. RCD
6.1 RCD 432: Rabbit Haemorrhagic Disease (RHD) Virus - infectivity trial in cats
| Programme Title: | Rabbit Haemorrhagic Disease (RHD) Virus - infectivity trial in cats |
| Programme Leader: | Dr Tao Zhenge |
| Institution: | AgResearch |
Summary
Previous studies have shown that feral cats from RHD epidemic areas in New Zealand have antibodies against RHD virus and RHD virus-positive cat liver has been identified by RT-PCR. To assess the possibility that the RHD virus may replicate in cats, a challenge trial was carried out by feeding cats with RHD virus positive rabbit livers. RHD virus-positive livers were collected from rabbits that died of RHD and were proven RHD virus-positive by RHD virus antigen specific immunoassay. Control livers were RHD virus-negative rabbit livers collected from sero-negative rabbits and proven negative by RT-PCR. Nine 16-18 weeks old female cats were involved in this trial. Three cats (Group A) were fed with RHD virus-negative livers at weekly intervals for 4 weeks and served as controls. Two cats (Group B) were fed with RHD virus-positive liver on day 0 and with RHD virus-negative livers for the following three weeks. Four cats (Group C) were fed with RHD virus-positive livers for 4 weeks. Blood samples were collected for serology throughout the trial. Liver, spleen, mesenteric lymph node, thymus, tonsil, lung, kidney, small and large intestines were collected at necropsy for the detection of RHD virus and for histopathology. All animals from Group B and C produced antibodies to RHD virus by 10 days after the first feed of RHD virus-positive rabbit livers. The results showed that animals fed RHD virus-positive livers for 4 weeks had higher RHD virus antibody titres than those fed these livers only on day 0. RHD virus genome could be detected from mesenteric lymph node, liver, spleen and tonsil by sense RT-PCR. Positive tissues were detected more frequently from samples collected soon after feeding the RHD virus-positive rabbit livers. A positive result for anti-sense RT-PCR was obtained from the mesenteric lymph node of one cat that was killed 2 days after the 4th feed of the RHD virus-positive livers. Anti-sense RT-PCR test identifies the complementary strand RNA of RHD virus genome, which is a necessary step for the replication of RHD virus. The positive result of the anti-sense RT-PCR suggested that RHD virus replicated in the mesenteric lymph node of the infected cats. Although RHD virus might have replicated in cats that fed with RHD virus-positive livers, no disease could be demonstrated as a consequence of such infection. Feral cats may play a role in the epidemiology of RHD by spreading RHD virus in their faeces.
Contact for Enquiries
Farm Monitoring Programme Manager
Monitoring and Evaluation
MAF Policy
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0623
Fax: +64 4 894 0741
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