Molecular and serological prevalence of Anaplasma marginale in cattle of North Central Morocco

A cross sectional study was conducted to investigate the epidemiological distribution of Anaplasma marginale in North Central Morocco. Blood samples from five provinces of Morocco were collected from apparently healthy cattle (n=668) and simultaneously analyzed by a nested polymerase chain reaction (nPCR) assay and competitive enzyme-linked immunosorbent assay (cELISA). The overall prevalence of A. marginale was 21.9% by nPCR and 16.5% by cELISA. The Kappa coefficient between nPCR and cELISA indicated a modest level of agreement (0.54). The prevalence of A. marginale varied significantly according to the province and the month of sampling. However age, gender and breed did not have a significant effect on the prevalence of this pathogen. The highest prevalence of A. marginale was found in the Gharb, a sub-humid area while the lowest was reported in the Saiss, a semi-arid area. These results indicate that an A. marginale infection are widespread in the country and suggests that either or both techniques are excellent tools for epidemiological studies and control programs.

Differential distribution of gamma delta T-cell receptor lymphocyte subpopulations in blood and spleen of young and adult cattle

A panel of monoclonal antibodies to bovine leukocyte differentiation molecules was used to evaluate peripheral blood and splenic lymphocytes from cattle of various ages. The major population of peripheral blood lymphocytes from neonatal calves was gamma delta T-cell receptor (TCR1) positive, as determined by TCR1-N12 expression. TCR1-N12+ lymphocytes were decreased in number in older calves, and were lowest in adult cattle. The major subpopulation of TCR1-N12+ cells from peripheral blood coexpressed WC1, but not BoCD2. A small subpopulation of peripheral blood TCR1-N12+ cells from cattle of all ages coexpressed BoCD2, but not WC1. The TCR1-N12+ BoCD2+ lymphocytes made up the largest TCR1-N12+ lymphocyte subpopulation in spleens of both calves and adults. The TCR1-N12+WC1+ splenic lymphocytes were present as a small population. The data indicate that two subpopulations of TCR1+ lymphocytes are present in cattle of all ages. These two subpopulations are differentially distributed between blood and spleen, with TCR1-N12+WC1+ lymphocytes predominating in blood, and TCR1-N12+BoCD2+ cells predominating in spleen.

Characterization of an Anaplasma ovis isolate from desert bighorn sheep in southern California

To understand the role of bighorn sheep (Ovis canadensis) in the epidemiology of anaplasmosis, we recovered a field isolate from a suspected enzootic area in southern California (USA). Whole blood was collected from three desert bighorn sheep (Ovis canadensis nelsoni) and inoculated into a susceptible splenectomized domestic sheep, calf and a susceptible spleen-intact bighorn sheep. No infection occurred in the calf, but a detectable infection developed in both the domestic sheep and bighorn sheep 24 days after inoculation. The infection in both domestic and bighorn sheep resulted in severe clinical disease but was resolved with the use of tetracycline. Using monoclonal antibodies and DNA probes, we confirmed that the isolate was Anaplasma ovis.

Susceptibility of two Rocky Mountain bighorn sheep to experimental infection with Anaplasma ovis

In North America, the role of wild ruminants in the epidemiology of anaplasmosis has not been clearly defined. Such information is particularly meager in regard to bighorn sheep. We report the susceptibility of two Rocky Mountain bighorn sheep (Ovis canadensis canadensis) to experimental infection with a well characterized field isolate of Anaplasma ovis obtained from domestic sheep in Idaho. Both bighorn sheep developed infection resulting in severe clinical disease, with relatively high parasitemias, icterus and anemia. One animal required tetracycline therapy and responded well to treatment, while the other recovered uneventfully without treatment. Both bighorn sheep were spleen-intact, a condition that in A. ovis-exposed domestic sheep typically is associated with mild infection. The results indicate that bighorn sheep may be adversely affected if exposed to the organism in nature.

A flow cytometric method for assessing viability of intraerythrocytic hemoparasites

We have developed a rapid, reliable method of evaluating growth and viability of intraerythrocytic protozoan hemoparasites. The assay involves the selective uptake and metabolic conversion of hydroethidine to ethidium by live parasites present in intact erythrocytes. The red fluorescence imparted by ethidium intercalated into the DNA of the parasite permits the use of flow cytometry to distinguish infected erythrocytes with viable parasites from uninfected erythrocytes and erythrocytes containing dead parasites. Comparison of the fluorochromasia technique of enumerating the number and viability of hemoparasites in cultured erythrocytes with enumeration in Giemsa-stained films and uptake of [3H]hypoxanthine demonstrated the fluorochromasia technique yields comparable results. Studies with the hemoparasite, Babesia bovis, have shown the fluorochromasia technique can also be used to monitor the effect of parasiticidal drugs on parasites in vitro. The cumulative studies with the fluorochromasia assay suggest the assay will also prove useful in investigations focused on analysis of the immune response to hemoparasites and growth in vitro.

Detection of Anaplasma-marginale-infected tick vectors by using a cloned DNA probe

Anaplasmosis is the most widely distributed of several important tick-borne diseases that constrain cattle production throughout much of the world. Evaluation of the effectiveness of disease control strategies that integrate vaccination with tick control requires the ability to monitor tick and cattle infection rates. To detect Anaplasma marginale in ticks and bovine erythrocytes, a 2-kilobase DNA fragment from a cloned A. marginale gene coding for a surface protein having a Mr of 105,000 was prepared and evaluated as a probe. The probe was species specific and detected A. marginale DNA derived from infected bovine erythrocytes and adult Dermacentor ticks infected either as nymphs or adults. Tick infection was confirmed by microscopy and test feeding on a susceptible calf. The sensitivity of the probe is suitable for detecting infected ticks in experimental and field epizootiology studies.