The Harlan colony consisted of 6- to 8-week-old female rats purchased from Harlan (Indianapolis, IN, USA) from an established colony

The Harlan colony consisted of 6- to 8-week-old female rats purchased from Harlan (Indianapolis, IN, USA) from an established colony. and incapable of amplification in equids (and spp. Epizootics and epidemics have occurred from southern North America to northern South America, and the VEEV strains involved have caused debilitating neurologic disease with high fatality rates in equids (spp., family Echimyidaeand cotton rats (spp., family Cricetidae) have been most often implicated as principal reservoir hosts for enzootic strains, based on seroprevalence and experimental infections demonstrating viremia adequate in titer and duration to infect enzootic mosquito vectors (spp. are found mainly in Panama, northern Peru, Bolivia, Paraguay, and Brazil; spp. are found mainly from southern North America to northern parts of Venezuela, Colombia, and Peru ((cotton rat) were used in this study: the Harlan colony, the Texas population, and the Florida population. The Harlan colony consisted of 6- to 8-week-old female rats purchased from Harlan (Indianapolis, IN, USA) from an established colony. Because the exact geographic origin was unknown, cytochrome B mitochondrial gene sequences were amplified by PCR and compared phylogenetically with those from cotton rats from various locations in North America (distribution [trapped in Galveston Island State Park, Texas (29.27N, 94.83W) (trapped in southern Florida (test, and analysis of variance were used to analyze data. Results Clinical Responses and Survival Inoculation of the Florida rats with 3 log10 PFU of VEEV strain 68U201 (IE) or Co97-0054 (ID) resulted in no detectable signs of illness and survival rates of 100% and 87.5%, respectively (Figure 1). One Florida rat inoculated with strain Co97-0054 died on day 10 postinoculation without exhibiting any signs of illness. These findings contrasted with the results of VEEV infections of the Texas and Harlan populations. Although the Harlan rats were inoculated with only the subtype ID strain, signs of severe illness developed in all of the Harlan and Texas rats beginning on day 5. Signs included ruffled coats, lack of grooming, lethargy, and for many, signs of encephalitis (incoordination and (R)-(+)-Corypalmine instability when walking and erratic movements of the head and limbs), dehydration (measured by lack of skin turgor), and anorexia. Most animals that died before day 5 postinoculation showed no prior signs of illness. The average survival time for the Texas population was 6.8 days after inoculation with the subtype ID strain and 8.2 days with the IE strain; for the Harlan colony, it was 5 days after inoculation with the subtype ID VEEV. None of the animals that survived past day 15 died. The 2 2 sham-inoculated and the 2 2 noninoculated rats survived without signs of disease. Open in a separate window Figure 1 Survival of cotton rats from Florida, Texas, and Harlan after subcutaneous inoculation with 3 log10 PFU of enzootic Venezuelan equine encephalitis virus (subtypes IE and ID). Neurovirulence in Florida Cotton Rats To determine whether the absence of disease in the Florida population was due to the inability of (R)-(+)-Corypalmine the virus to penetrate the central nervous system, 3 rats were inoculated intracranially with 3 log10 PFU/mL of subtype IE VEEV. Viremia titers at 24 h postinoculation were 6.3, 6.2, and 6.8 log10 PFU/mL (mean 6.5). By day 3 postinoculation, all of these rats started showing signs of illness, including ruffling of the (R)-(+)-Corypalmine fur and lack of movement. By day 9 postinoculation, 1 rat was dead and the other 2 exhibited instability and difficulty in walking, uncoordinated and erratic movements of the head and limbs, dehydration, and anorexia; these animals were euthanized because of the severity of disease. Histopathologic examination of the brains showed clear signs of encephalitis, focal meningoencephalitis (Figure 2, (R)-(+)-Corypalmine panels A, B) and associated perivascular mononuclear cell infiltration (Figure 2, panel C), and neurophagia, which led to the conclusion that the cause of death was from the viral Rabbit polyclonal to Synaptotagmin.SYT2 May have a regulatory role in the membrane interactions during trafficking of synaptic vesicles at the active zone of the synapse. infection and not from the injection or manipulation of the animals. Open in a separate window Figure 2 Histologic staining (hematoxylin and eosin) of Florida cotton rat tissues 9 days after intracranial inoculation with 3 log10 PFU of enzootic Venezuelan equine encephalitis virus (subtype IE). A) Inflammation of the meninges (arrows). B) Inflammation of the meninges and dilated blood vessels (arrows). C) Perivascular cuffing of blood vessels (arrow). D) Brain from a noninfected rat. (Magnification 40.) Dose Dependence To determine whether the Florida populations apparent resistance to VEE after peripheral illness was dose-dependent, 8 additional animals were inoculated with 5 or 6 log10 PFU (4 animals.