As one of America’s most devastating economic cattle diseases, anaplasmosis has reached critical impact levels in many regions, with researchers finding higher infection rates and dozens of separate strains. The disease is primarily spread via insects, veterinarians say, but producer unawareness and mismanagement are increasingly contributing factors.
“Producers can unwittingly spread the disease among their herd through vaccinations if needles aren’t disinfected or changed,” says Hans Coetzee, DVM, Kansas State University.
At least one estimate puts the economic cost of anaplasmosis to U.S. cattlemen at $300 million annually.
The losses can range from poor animal performance to abortions, bull infertility and cow deaths. If anaplasmosis invades a previously uninfected herd, research suggests the calf crop is reduced by 3.6%, the cow culling rate will increase 30%, and 30% of the adult animals showing signs will die.
“Because of a slow, six to eight-week incubation period, anaplasmosis often turns up in cattle herds in late summer, as the disease emerges in herds exposed to ticks or other vectors,” Coetzee says.
However, outbreaks of the disease do not always follow conventional wisdom, and some producers have seen anaplasmosis outbreaks much earlier in the year.
When an outbreak occurs, antibiotics are an effective treatment, especially when administered early. Prevention, however, is the key to reducing potential losses, and that might include vaccinations with an experimental vaccine available in 26 states and Puerto Rico.
Caused by a blood parasite, anaplasmosis is found worldwide, and in 48 states in the U.S. Anaplasma marginale is the most common pathogen of cattle, but researchers have discovered over 100 strains and suspect there are many more.
The disease is transmitted from animal to animal by biting flies, ticks and contaminated needles or surgical instruments. Infected animals might not show clinical signs, but once infected the animal will be a carrier of the disease for life.
An infected animal’s immune system attacks the invading parasite, but also destroys infected red blood cells. In an acute infection, the loss of red blood cells inhibits the animals’ ability to provide adequate oxygen to tissues, and death occurs due to suffocation at the cellular level.
First discovered in the U.S. in 1925, anaplasmosis has long been considered a disease in the Southeast. Recent studies, however, show the disease firmly rooted in Midwestern and Western states, too.
A study conducted by Kansas State University’s College of Veterinary Medicine Diagnostic Lab, involving 169 participating veterinarians and 870 cattle herds in 2017, found a high rate of infection. Kansas State University veterinarian Gregg Hanzlicek says the results revealed “the apparent seroprevalence at 70% to 80% in the eastern third of the state, which isn’t a big surprise for veterinarians who practice in those areas.”
Moving westward, the Kansas research found diminishing—yet surprising—levels of “sero-prevalence” of the disease in cattle. Central Kansas had 43% to 56%, while western Kansas showed a “sero-prevalence” range of 18% to 34%, a level Hanzlicek said was shocking.
Risk of Cattle Contracting Anaplasmosis Grows
This interactive map shows the greatest risk areas for anaplasmosis infections. Every state, except Hawaii has reported cases of anaplasmosis in cattle. An experimental vaccine from University Products LLC has been approved for veterinarian use in 26 states and Puerto Rico. Roll over each state to see more information. (Produced by Lori Hays)
The incidence of anaplasmosis might not reach those levels in other states, but veterinarians warn the disease is so costly precautionary measures should be implemented. One of the first recommendations is to implement an effective parasite control program. Veterinarians say ticks are the primary vectors for biological transmission because they serve as amplifiers of the disease.
The second mode of transmission is mechanical, Hanzlicek says, mostly involving horse, stable and deer flies. “Flies don’t amplify the organism like the ticks do, so the bacteria those flies pick up when feeding is the maximum they will be able to pass on to the next animal when they take their blood meal.”
Additionally, Hanzlicek says needles play a role in mechanical transmission. According to one research project, six out of 10 animals became infected just from the movement of the needle from a positive animal to a negative animal.
“At least from this study, if you have a positive animal in the chute, and you have a negative animal behind it and you’re not disinfecting or changing needles, there is a 60% probability that the animal behind it will become positive. Needles are a big deal in positive herds.”
Veterinarians also recommend feeding a mineral mix containing the antibiotic chlortetracycline(CTC). Feeding CTC at a rate of 0.5 mg per pound of body weight will control active infections. A Veterinary Feed Directive (VFD) is required for use of CTC.
Despite using the recommended antibiotic-mineral mix with a VFD to prevent anaplasmosis infections, manager Jason Lewis says the Division Ranch, Strong City, Kan., lost 13 cows last year to the disease. ( Greg Henderson )