Source: by PJ Griekspoor for American Agriculturalist|May 30, 2019
Bovine anaplasmosis, a vector-borne bacterial infection that causes often-fatal illness in cattle, is re-emerging as a threat across the U.S., including all regions in Kansas.
The disease, which caused major losses for beef producers in the 1960s and 1970s, is vectored by biting flies and ticks, but can also be transmitted from one animal to another by dehorning tools, castration tools, ear tagging equipment or vaccination needles if they are not sterilized between animals.
During an all-day symposium in Manhattan, newly minted veterinarian Mark Spare shared details from his graduate research on the prevalence and management of the disease in Kansas.
Spare said submission of samples from Kansas herds showed a sharp increase in the years from 2013 to 2015, and his project was completed from Oct. 1, 2016, to March 1, 2017.
The research divided the state into nine districts and tested 10 cows from each of the 925 herds across Kansas utilizing the help of 164 volunteer veterinarians, who collected two blood samples from a total of 9,250 cows during routine annual activities such as pregnancy diagnosis or vaccinations.
The survey also asked 41 closed-ended questions and 3 open-ended questions of producers to determine herd demographics, preventive control measures, pasture management and more to attempt to learn whether pasture management, feeding, movement or other management issues had an impact on the level of infection.
The survey results show that the highest rate of infection is in eastern Kansas, which is expected because that’s where the Flint Hills pastures and the highest rainfall are located — factors that result in both numbers of cattle and lucrative environment for ticks and flies.
More than 80% of the herds surveyed in northeast Kansas had at least one infected animal. The lowest rates were in the middle far-western district which has a comparatively arid environment and a decreased stocking rate.
The herds most likely to be infected were those that used insecticide ear tags, used vaccines and burned pastures.
“These are not causative results,” Spare said. “They are indicative of the regions of infection and what management practice were commonly used in infected herds.
Spare said the research results indicate that Kansas has a statewide prevalence of anaplasmosis at the cow herd level. But he said it did not measure total infection, merely the rate at which herds had at least one infected cow.
He said the study showed that some practices show a higher rate of infection: herds that are vaccinated herds that graze on burned pastures and herds that have insecticide ear tags. However, those herds also exist in the highest risk areas for tick population and areas that have a history of infection.
Economic consequences
Dr. Hans Coetzee, professor at Kansas State University, talked about the economic impact that anaplasmosis has on Kansas and the country.
Coetzee documented the multiple trials of losses to the dairy and beef industries from separate studies of infection in both dairy and beef herds. They include both active losses from the death of cattle and calves to the passive losses of decreased fertility, increased abortion rates and loss of milk production from infected cattle.
Anaplasmosis causes direct cattle death, loss of calves due to aborted pregnancies, lost milk production in dairy cows, lost ability to export cattle and increased cost of herd management because of the need for vaccines or antibiotic treatment, Coetzee said.
In naïve herds, the death rate is high. In a 2010 study of a newly infected dairy herd, 34% of the lactating cows died. Milk production loss was 44%.
In that study, the producer called for help after the initial sudden deaths. The veterinarian immediately noticed that six of the remaining cows had pale mucous membranes, jaundice and anorexia, and suspected anaplasmosis, which was confirmed with a blood smear.
In a beef herd study in 2012, a Florida producer had recently purchased cattle in Texas and co-mingled them with his herd. Because anaplasmosis is endemic in Florida, it was assumed that his herd would be positive for the bacteria and therefore immune, Coetzee said. Unfortunately, he was mistaken.
After 18% of one of his beef herds died, he called for help and tests confirmed that anaplasmosis was to blame.
“When your ratio of uninfected to infected animals is between 1:1 and 1:2, you start to see deaths,” he said. “As more animals in the herd recover, the rates of new infection drop as endemic stability is reached.”
Treatment is a dose of long-acting oxytetracycline. Animals who recover are carriers but are generally immune to acute infection.
Management is tricky
Deciding how to manage a herd after an outbreak can be difficult.
Basically, you have to decide if you want to live with a carrier herd or if you want to attempt to eliminate the disease, he said. The problem is, if you eliminate the disease then the remaining cattle are susceptible to re-infection. If you live in an area where there are biting flies, ticks and wildlife, then you have to establish control measures to prevent re-infection.
That means feeding a mineral supplement of chlortetracycline, taking measures to control insect populations and moving cattle seasonally to pastures with the lowest insect pressure.
“As a general rule, the more prevalent anaplasmosis is in a given region, the harder it is to prevent infection,” Coetzee said. “That means, if you are a commercial beef operation, it may be less expensive and more practical to maintain a positive herd. This can be achieved by ensuring that calves under 12 months of age are given an opportunity to acquire the infection naturally when they are least likely to develop fatal clinical disease.”
“Alternatively, chlortetracycline medicated mineral can be strategically deployed at times in the vector season when the disease is most likely to be transmitted. This will allow animals to become infected but will limit the development of clinical disease.”
This approach may not work for seed stock producers and ranchers who regularly sell cattle, however. Cattle that test positive should not be sold or moved in case these are responsible for introducing infection into naïve herds. That means a rancher would have to treat a carrier animal to eliminate the disease before that animal could be sold.
For those producers, feeding a medicated mineral continuously to prevent infection could be a better option. Even that is not without challenges, however.
“It’s difficult to know that every cow is consuming the right amount of the mineral,” Coetzee said. “In pastures with good grass, the animals may simply consume too little mineral to get an effective dose. Then, if they are exposed, they could get sick and die.”