North American Veterinary Licensing Examination (NAVLE) Practice Test

Anaplasmosis is a disease caused by the bacteria Anaplasma marginale, which primarily affects cattle and can lead to significant health issues, including anemia and icterus (jaundice). In older cows, the immune response may be compromised, making them more susceptible to diseases like anaplasmosis. The condition typically presents with symptoms such as weight loss, weakness, and pale mucous membranes, which can be observed during a physical examination.

In Texas, where the climate and cattle management practices can predispose herds to this disease, anaplasmosis is particularly prevalent. The organism infects red blood cells, leading to their destruction, which results in anemia. The jaundice observed in these animals is due to the breakdown of hemoglobin from the destroyed red blood cells, causing an accumulation of bilirubin in the bloodstream.

While options like Eperythrozoon spp. and Theileriosis can also cause similar symptoms, they are less commonly associated with older cattle in Texas compared to anaplasmosis. Leptospira icterohaemorrhagiae can cause icterus, but it is usually linked to acute infections rather than chronic conditions in older cows, making it a less likely diagnosis in this context.