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Date:Mon, 2 Dec 2002
Posted by: Lois Levitan (lcl3@cornell.edu)

WNV IN REPTILES WNV infection was confirmed for the first time in reptiles in the US when Florida public health veterinarian Lisa Conti confirmed on Nov 12 that 3 American alligators from a commercial alligator farm in Central Florida were diagnosed with WNV infection in October. The story was first reported Nov 13 by the Florida Times-Union and Reuters News Service, picked up by a number of (mostly) Florida papers, and subsequently discussed on the ProMED listserv. As of December 2, 2002 web searches did not locate any official follow-up. The following summary is primarily drawn from the Nov 13 news item and the ProMED discussion, as well as from material on ERAP's WNV web pages.

DIAGNOSIS Diagnostic tests performed by several agencies contributed to the WNV diagnosis. These include University of Florida, College of Veterinary Medicine (UF); Florida Department of Health (FDH) and the Centers for Disease Control and Prevention (CDC)

(1) necropsy and histologic changes (UF),(2) positive immunhistochemistry on brain sections (UF);(3) positive polymerase chain reaction (PCR) results on one brain and one spinal cord from two animals (FDH);(4) PCR on multiple tissues of all animals (CDC);(5) viral isolation (multiple tissues, all animals) (FDH)(source University of Florida, College of Veterinary Medicine).

ALLIGATOR DEATHS Epidemiological investigation is continuing to determine the extent and significance of WNV as a cause of death in alligators. Florida state vets are encouraging testing of alligators showing neurological symptoms of WNV infection. The tests that turned up the WNV-infected alligators were conducted after an unusual spate of deaths at the farm. Farm owners told officials that hundreds of alligators on their farm and elsewhere have died suddenly in the last 4 years.

Whatever the cause of deaths, state officials are still trying to gauge the potential impact of the die-off on Florida's 21 commercial alligator farms, which produced 25 200 hides and 190 600 pounds (85 770 kg) of meat in 2001. Florida veterinarians are quoted as saying there is little chance of contracting WNV by eating the meat of an infected alligator because cooking destroys the heat-sensitive virus.

DISCUSSION re ECTOTHERMAL REPTILES & VIRUSES ProMED posted some contradictory evidence regarding the likelihood that viruses affecting endothermic mammals and birds are also found in ectothermic reptiles. S. Gerard notes that it is unlikely, seemingly due to the wide variation in body temperature of ectotherms, providing an unfavorable environment for these pathogens. Gerard cites work showing that garter snakes were unable to sustain Western equine encephalitis virus (WEE) through winter and hibernation (source Steve Gerard, Nov 16 ProMED posting).

In contrast, C. Calisher notes that there are many papers in the literature recording isolation of various arboviruses from reptiles. He offers the following examples from several research groups High-titer viremias of long duration have been observed in snakes, lizards, alligators, and turtles. Garter snakes and spotted turtles experimentally infected with Western equine encephalitis virus developed viremias that were dormant during winter and reactivated in spring (or when warmed up). Infected garter snakes were able to transmit WEE to uninfected Culex tarsalis mosquitoes that fed on them (i.e., they could complete a transmission cycle) and young born to naturally infected snakes were shown to be infected (i.e., transovarial transmission). WEE was isolated from 84 snakes of three genera in Utah and from Texas tortoises dug from sand in south Texas where they were hibernating.

Neutralizing antibodies to Eastern equine encephalitis (EEE) were detected in serum samples from 5 snakes, one turtle, and one alligator collected in the Okefenokee Swamp, Georgia, and from in lizards in Panama. While Hayes et al. found that only 1 in 190 serum samples from reptiles had antibodies to EEE, experimentally-infected reptiles were highly susceptible to infection (source Charlie Calisher(calisher@cybersafe.net) posting to ProMED, Nov 20, 2002. For details and references see ProMED-Id 20021121.5859).

Of perhaps related relevance, Hubalek andHalouzka (1999) cite an article in Russian by Kostyukov et al. (1986) noting that frogs (the amphibians Rana ridibunda) can harbor West Nile Virus and transmit it to Culex pipiens mosquito (Hubalek, Z. and J. Halouzka. September-October 1999. West Nile Fever - A Reemerging Mosquito-Borne Viral Disease in Europe. Emerging Infectious Diseases 5 (5) 643-650. http://www.cdc.gov/ncidod/EID/vol5no5/hubalek.htm).

ALLIGATOR BIOLOGY & FARMING Larger reptiles such as the American alligator are very adept at thermoregulation. Moreover, some alligator farming operations use heated slabs that maintain the alligators at steady body temperatures in the mid to high 90s, at a level very similar to the body temperatures of birds and mammals. The heated conditions enable the alligators to grow faster, feeding year round and in more abundance than they would naturally. Also, alligators are typically in or near to stagnant water, in close proximity to ideal conditions for abundant mosquito populations (source Steve Grenard (sgrenard@si.rr.com)in Nov 16 posting to ProMED, citing Medical Herpetology, NG Publishing, 1994 and S. Grenard's Handbook of Alligators and Crocodiles, Krieger 1990).

Given the evidence for Flaviviruses in reptiles, Calisher asks why Australians have not observed die-offs in farmed crocodilians due to Kunjin virus, which is considered a genotype of WNV. He posits that it could be due to slight differences between the genetic code of Kunjin and WNV in genes specifying differences in crocodialians. Or it could be due to Australian (captive and free) wildlife having established some sort of equilibrium with the Kunjin virus over time, which he suggests may eventually happen in North America also.

-- Lois Levitan, PhD       Program LeaderEnvironmental Risk Analysis ProgramCenter for the Environment213 Rice Hall, Cornell UniversityIthaca, New York USA 14853-5601Phone   (607) 255-4765     Fax (607) 255-0238Email	LCL3@cornell.eduProgram Email envrisk@cornell.eduWebhttp//www.cfe.cornell.edu/ERAP

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