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. 2009 Apr;15(4):519-25.
doi: 10.3201/eid1504.081008.

Experimental infection of potential reservoir hosts with Venezuelan equine encephalitis virus, Mexico

Eleanor R Deardorff  1 , Naomi L Forrester, Amelia P Travassos-da-Rosa, Jose G Estrada-Franco, Roberto Navarro-Lopez, Robert B Tesh, Scott C Weaver
Affiliations

Experimental infection of potential reservoir hosts with Venezuelan equine encephalitis virus, Mexico

Eleanor R Deardorff et al. Emerg Infect Dis. 2009 Apr.

Abstract

In 1993, an outbreak of encephalitis among 125 affected equids in coastal Chiapas, Mexico, resulted in a 50% case-fatality rate. The outbreak was attributed to Venezuelan equine encephalitis virus (VEEV) subtype IE, not previously associated with equine disease and death. To better understand the ecology of this VEEV strain in Chiapas, we experimentally infected 5 species of wild rodents and evaluated their competence as reservoir and amplifying hosts. Rodents from 1 species (Baiomys musculus) showed signs of disease and died by day 8 postinoculation. Rodents from the 4 other species (Liomys salvini, Oligoryzomys fulvescens, Oryzomys couesi, and Sigmodon hispidus) became viremic but survived and developed neutralizing antibodies, indicating that multiple species may contribute to VEEV maintenance. By infecting numerous rodent species and producing adequate viremia, VEEV may increase its chances of long-term persistence in nature and could increase risk for establishment in disease-endemic areas and amplification outside the disease-endemic range.

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Figures

Figure 1
Figure 1
Survival rates and weight change of wild rodents from Chiapas, Mexico, after experimental infection with 3 log10 PFU of Venezuelan equine encephalitis virus subtype IE, strain MX01-22. A) Survival rates. Black and yellow lines represent animals whose brains yielded live virus after necropsy. Red, green, blue, and purple lines indicate animals whose death was attributed to manipulation and/or stress, not to VEEV infection. B) Weight change. Mean cohort weight (grams) divided by mean cohort starting weight (day 0). Weight gain or loss was used as an indicator of disease. Only Baiomys musculus rodents showed weight loss during acute infection. Data for days 42 and 66 (not shown) did not differ significantly from that for day 28. Error bars indicate SEM.
Figure 2
Figure 2
Mean viremia profile (red lines) and mean hemagglutination inhibition (HI) antibody profile (blue lines) of 5 species of wild rodents after experimental infection with 3 log10 PFU of Venezuelan equine encephalitis virus type-IE, strain MX01-22. Black dashed lines indicate approximate mosquito infection viremia threshold for the enzootic vector Culex (Melanoconion) taeniopus. Fractions represent proportion of total cohort that had measurable response. Data for days 42 and 66 (not shown) did not differ significantly from data for day 28. Error bars indicate SEM.
Figure 3
Figure 3
Relatedness of 7 wild rodent genera that have been experimentally evaluated for suitability as amplifying hosts in enzootic transmission cycles of Venezuelan equine encephalitis virus. The 5 genera included in this study are presented in boldface; the 3 novel genera are underlined.
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