Because of a six- to eight-week incubation period, anaplasmosis often turns up in cattle this time of year, as the disease emerges in herds exposed to ticks or other vectors during the summer.
However, Kansas State University veterinarian Hans Coetzee says outbreaks don’t always follow conventional wisdom in terms of when, where and how infections occur. Coetzee presented the information during the annual American Association of Bovine Practitioners conference in September. In keeping with the conference theme of “What We Know that Isn’t So,” he set out to bust common myths regarding anaplasmosis.
The myths include:
- Anaplasmosis outbreaks occur almost exclusively in the Southeastern region of the U.S.
- Ticks are the predominant vector in spreading the disease.
- The only way to control anaplasmosis in endemic areas is to feed chlortetracycline (CTC) year-around.
The pathogen causing anaplasmosis, anaplasma marginale, is a rickettsiales bacteria that infects red blood cells. Coetzee says the pathogen spread from Southern Africa to Europe, and was first recognized in the U.S.—in Kansas—in 1925. It now occurs in 48 states and causes an estimated $300 million per year in morbidity and mortality. There are no vaccines on the market, and tetracyclines are the only approved treatments.
In the U.S., the pathogen is endemic to the Southeast, but outbreaks occur in Kansas and across the Plains, Midwest and Mountain regions, Coetzee says. A recent study in southern states indicates an overall prevalence rate around 16%. However, Coetzee notes testing in Florida found some herds with 80% positive infection rates while other herds, even those in the same management system but on different pastures, tested 80% negative.
Ticks are a primary carrier of the anaplasma marginale pathogen and biting insects can transfer the organism mechanically, but Coetzee says studies and field experience implicate needles as a common source of the infection. In a Kansas State University trial, for example, researchers used the same needles on animals known to be infected and healthy. About 60% of the healthy animals exposed to the infected needles contracted anaplasmosis. In a similar trial using needleless syringes, the infection rate in healthy animals was zero.
A PCR test can detect the organism sooner after infection and provide fewer false-positive results compared with the competitive ELISA test, Coetzee says. However, the PCR test comes at a higher price of approximately $35 per test. The Kansas State University lab, he notes, provides a pooled test for groups of five cattle to reduce cost.
When treating anaplasmosis with CTC, Coetzee reminds producers to ensure feed formulations and treatment protocols adhere to approved label specifications. Chemosterilization, or total elimination of the pathogen from a herd, is not necessary and unrealistic. “You can live with a carrier herd,” he says, by using testing, targeted on-label treatment, vector control and injection biosecurity, particularly in endemic areas.