Strongyloidiasis in cotton rats (Sigmodon hispidus) from central Oklahoma

Anaplasma bovis and Bartonella spp. in Libyan Jirds (Meriones libycus) from China

Anaplasma bovis (1), Bartonella krasnovii (3), and Bartonella sp. (17) were detected in 80 Libyan jirds (Meriones libycus) from China. These findings extend the known host and geographic ranges of these pathogens, with neither A. bovis nor B. krasnovii previously confirmed in Libyan jirds.

Stomach nematodes of cotton rats: parasites, commensals, or mutualists?

We related presence and burden of stomach nematodes to body mass and reproductive allocation in hispid cotton rats (Sigmodon hispidus) from two long-running field studies in Virginia (1983–1984, n = 286; and 1988–1990, n = 425) and one from Georgia 1987–1989 (n = 459). Eighty percent of rats from the earlier Virginia sample were infected, with mean nematode mass of 1,311 mg. In the later samples, 23% (Virginia) and 33% (Georgia) were infected with mean nematode mass of 493 and 769 mg, respectively. Presence of nematodes was positively correlated with host body length for each sex in each sample. We used analysis of covariance to examine length-adjusted residuals for presence of nematodes and mass of nematodes for association with somatic and reproductive response variables. Both body and reproductive masses were either positively associated or not related to nematode presence in the two low-prevalence samples, and either negatively associated or not related to nematode presence in the high-prevalence sample. No relationships were detected between host mass and nematode mass per host in either sex in any sample. There was no effect of nematode presence on litter size of pregnant females, but there was a positive effect of nematode mass on litter size in Georgia. Recent theory provides several possible explanations for such neutral-to-positive effects of stomach nematodes on host fitness, including the evolution of host tolerance to the parasites, fecundity compensation by the hosts, and positive effects on host health via immune modulation.

Efficacy of histopathology in detecting petrochemical-induced toxicity in wild cotton rats (Sigmodon hispidus)

A variety of chemical mixtures exist in the soil of petrochemical waste sites, and many of these compounds are known immunotoxicants that have been observed to induce immune alterations in wild rodents inhabiting many of these petrochemical waste sites. Conventional histopathological assessments have been widely used with considerable success to investigate immunotoxicity of various agents under laboratory conditions. We hypothesized that histopathologic assessments would be equally sensitive for detecting exposure to complex mixtures of toxicants in cotton rats (Sigmodon hispidus) residing in contaminated habitats. Histopathological parameters were examined from a total of 624 cotton rats that were seasonally collected from 13 petrochemical-contaminated waste sites and 13 ecologically matched reference sites in Oklahoma over a 3-year period. Histopathological examination did not reveal any lesion associated with exposure to petrochemical wastes except renal inclusion bodies. Prevalence and severity of histologic lesions in liver and kidneys of cotton rats were significantly influenced by season, where prevalence and severity were lower in winter than summer on all study sites. These results suggest that the evaluation of toxicity from exposure to contaminants in the soil of industrial waste sites using histopathological assessments is not sensitive enough to detect exposure to the low levels of environmental contaminants present on most waste sites.

Fluorosis in a wild cotton rat (Sigmodon hispidus) population inhabiting a petrochemical waste site

We have developed an in situ mammalian model for evaluating environmental contamination using wild cotton rats. In a series of experiments, 200 male cotton rats were captured during 4 collection periods (spring 1991 = 35; fall 1991 = 60; spring 1992 = 53; fall 1992 = 52). A total of 103 of these cotton rats were captured from control sites, and the remaining 97 were captured from an abandoned oil refinery. All sites were located in the vicinity of Cyril, Oklahoma. There were alterations in the incisors of cotton rats captured from the refinery site. Normal color of cotton rat incisors is deep yellow-orange, which is imparted by a pigment normally produced by ameloblasts. Grossly, the upper incisors of 37 of 97 rats and lower incisors of 54 of 97 rats were affected. The affected incisors were white, chalky, and thin with striations and erosions of the enamel. Microscopic examination revealed that there were dysplastic and necrotic changes in the ameloblasts. The bone fluoride levels were significantly higher in rats captured from the refinery as compared to the rats captured from the control sites.