West Nile virus in farmed alligators

Abstract

Seven alligators were submitted to the Tifton Veterinary Diagnostic and Investigational Laboratory for necropsy during two epizootics in the fall of 2001 and 2002. The alligators were raised in temperature-controlled buildings and fed a diet of horsemeat supplemented with vitamins and minerals. Histologic findings in the juvenile alligators were multiorgan necrosis, heterophilic granulomas, and heterophilic perivasculitis and were most indicative of septicemia or bacteremia. Histologic findings in a hatchling alligator were random foci of necrosis in multiple organs and mononuclear perivascular encephalitis, indicative of a viral cause. West Nile virus was isolated from submissions in 2002. Reverse transcription-polymerase chain reaction (RT-PCR) results on all submitted case samples were positive for West Nile virus for one of four cases associated with the 2001 epizootic and three of three cases associated with the 2002 epizootic. RT-PCR analysis was positive for West Nile virus in the horsemeat collected during the 2002 outbreak but negative in the horsemeat collected after the outbreak.

Figure 1

Perivascular changes observed within the brain of alligators infected with West Nile virus (400x). A. Perivascular infiltrates were composed of primarily lymphocytes, plasma cells, and macrophages in the hatchling alligator. B. Perivascular infiltrates were composed of primarily heterophils (arrows) in juvenile alligators.

Figure 2

West Nile virus (WNV) reverse transcription-polymerase chain reaction results from epizootic die-offs in farm-raised alligators. The expected amplicon is 248 bp. Lane 1, a 100-bp molecular weight ladder. Lane 2, the positive WNV control. Lane 3, fresh tissue samples from a juvenile alligator in the 2002 epizootic. Lane 4, virus isolation cell homogenate from a juvenile alligator in the 2002 epizootic. Lane 5, horsemeat that was being fed to alligators during the 2002 epizootic. Lane 6, initial postepizootic horsemeat shipment. Lanes 7, 8, and 9, formalin-fixed, paraffin-embedded tissues of juvenile alligators in 2001 and 2002. Lane 10, fresh tissue from a wild alligator. Lane 11, negative WNV control.