Detection and quantitation of Anaplasma marginale in carrier cattle by using a nucleic acid probe

Abstract

Cattle which have recovered from acute infection with Anaplasma marginale, a rickettsial hemoparasite of cattle, frequently remain persistently infected with a low-level parasitemia and serve as reservoirs for disease transmission. To fully understand the role of these carriers in disease prevalence and transmission, it is essential that low levels of parasitemia can be accurately detected and quantitated. We have developed a nucleic acid probe, derived from a portion of a gene encoding a 105,000-molecular-weight surface protein, that can detect A. marginale-infected erythrocytes. The probe is specific for A. marginale and can detect 0.01 ng of genomic DNA and 500 to 1,000 infected erythrocytes in 0.5 ml of blood, which is equivalent to a parasitemia of 0.000025%. This makes the probe at least 4,000 times more sensitive than light microscopy. Hybridization of the probe with treated blood from animals proven to be carriers of anaplasmosis showed that parasitemia levels were highly variable among carriers, ranging from >0.0025 to <0.000025%. Parasitemia levels of individual animals on different dates were also variable. These results imply that, at any given time, individuals within a group of cattle may differ significantly in their abilities to transmit disease.

A Review of Bovine Anaplasmosis

“…Throughout the remainder of the persistently infected carrier’s life there are relatively uniform cycles over a 10‐ to 14‐day period of increasing and decreasing numbers of circulating erythrocytes infected with the parasite (Kieser et al., 1990; Viseshakul et al., 2000; Kocan et al., 2003). The concentration of infected erythrocytes varies markedly at bimonthly intervals from 10 3 to 10 5 infected cells per millilitre of blood (Eriks et al., 1989), much lower than in the acutely infected animal (Scoles et al., 2005a).…”

Insights into Mechanisms of Bacterial Antigenic Variation Derived from the Complete Genome Sequence of Anaplasma marginale

“…2,18 This cycle of emergence and control continues unabated, allowing life-long persistent A. marginale infection. 2,16,18,22…”

Induction of protective immunity by using Anaplasma marginale initial body membranes

“…The disease is caused by the rickettsia Anaplasma marginale and is characterized by intraerythrocytic rickettsemia, anemia, weight loss, and death of infected cattle (24,31). Recovered animals remain carriers of anaplasma and act as reservoirs of infection for tick transmission to susceptible cattle (3,8,33). Anaplasmosis control in Africa is based on intensive application of acaricides to kill the tick vectors and prevent transmission of disease (14,15).…”