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  • Author or Editor: Nathan C. Nieto x
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Abstract

Objective—To determine whether sequelae of infection differed among single versus double infection with Anaplasma phagocytophilum or Anaplasma marginale, with and without tick salivary extract, in cattle.

Animals—Eighteen 13-month old steers.

Procedures—Treatment groups of 3 cattle each included A marginale inoculated ID followed on day 35 by A phagocytophilum without tick saliva, A phagocytophilum followed on day 10 by A marginale without tick saliva, A marginale followed on day 35 by A phagocytophilum with tick saliva, A phagocytophilum followed on day 10 by A marginale with tick saliva, tissue culture control injection, and tick saliva control injection. Infection was monitored via clinical observations, CBC, serologic testing, and PCR analysis of blood and tissues.

Results—Infected cattle had significantly reduced weight gain. Anemia occurred 25 to 32 days after A marginale infection, which was attenuated by tick saliva. Parasitism was greater if cattle had not previously been inoculated with A phagocytophilum. Nine of the 12 treated cattle had positive results of PCR analysis for A phagocytophilum from at least 1 blood sample. Five tissue samples had positive results of PCR analysis for A phagocytophilum; PCR results for A marginale were positive in spleen, lung, lymph node, heart, and ear skin of infected cattle.

Conclusions and Clinical Relevance—Results indicated an important biological interaction between A marginale and A phagocytophilum infection as well as with tick saliva in disease kinetics and severity in cattle, which may be important for interpretation of diagnostic tests and management of disease in areas where both pathogens occur.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate disease progression in sheep experimentally inoculated with Anaplasma phagocytophilum and determine the Anaplasma spp seroprevalence in sheep in free-ranging flocks in the Sierra Nevada foothills and Oregon Coast Range.

Animals—10 mature ewes seronegative for Anaplasma spp and 251 sheep from 8 flocks.

Procedures—10 ewes received 1 of 3 treatments: A phagocytophilum Webster strain (n = 4), A phagocytophilum MRK strain (4), or human promyelocytic leukemia cells (control treatment [2]). Sheep were monitored for signs of clinical disease, and blood samples were obtained for serologic and PCR assay evaluation intermittently for 48 days. From a subsample of sheep from each of 8 free-ranging flocks, blood samples were obtained to determine Anaplasma spp seroprevalence.

Results—Sheep inoculated with A phagocytophilum developed subclinical or mild disease, whereas sheep inoculated with the control treatment did not develop any signs of disease. Only 2 ewes seroconverted; both had received the MRK strain. Anaplasma-specific DNA was detected in blood samples from 1 sheep in the Webster strain–inoculated group and 3 sheep in the MRK strain–inoculated group. Sheep seropositive for Anaplasma spp were detected in 5 of 8 flocks, and flocks in the Sierra Nevada foothills had higher within-flock seroprevalence (22%) than did flocks in the Oregon Coast Range (6.4%).

Conclusions and Clinical Relevance—Infection with A phagocytophilum in mature sheep generally resulted in subclinical disease. Higher Anaplasma spp seroprevalence in sheep in the Sierra Nevada foothills corresponded to the geographic distribution of anaplasmosis reported for dogs, horses, and humans.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate clinical, microbiologic, and pathologic outcomes in mice after inoculation with 4 equine-origin Corynebacterium pseudotuberculosis strains.

Animals—15 C3H/HeJ mice.

Procedures—In a preliminary study, the optimum route of inoculation was determined. In the main study, mice were allocated to 4 treatment groups (3 mice/group). One slow- or rapid-growing equine-origin C pseudotuberculosis strain was inoculated ID into the mice of each treatment group.

Results—All 4 strains had distinct tropism for the liver. Histologic lesions associated with rapid-growing strains included focally extensive unencapsulated areas of acute, massive coagulative necrosis of hepatocytes with intralesional colonies of bacteria and variable portal hepatitis characterized by accumulations of mononuclear and polymorphonuclear inflammatory cells. In contrast, the livers of mice inoculated with slow-growing strains had multiple discrete, randomly distributed foci of hepatocellular necrosis and neutrophilic hepatitis that were considerably less severe than the lesions in the mice inoculated with the rapid-growing strains. Significantly more bacterial colonies were recovered from the organs of mice inoculated with rapid-growing than with slow-growing strains of bacteria. Bacteria were isolated from the liver, spleen, lungs, and mesenteric lymph nodes of mice inoculated with rapid-growing strains and from the liver and lymph nodes of mice inoculated with slow-growing strains.

Conclusions and Clinical Relevance—Study of host-bacteria interactions in hosts that are naturally infected with C pseudotuberculosis is difficult because of underlying genetic variability among animals, expense, and requirements for multiple replicates and control animals. The C3H/HeJ mice may provide a useful means for studying virulence mechanisms of C pseudotuberculosis.

Full access
in American Journal of Veterinary Research