Anaplasmosis outbreaks typically peak in late summer through early fall, and now is a good time to review control strategies based on risk levels. Kansas State University veterinarian Hans Coetzee, BVSc, Cert CHP, PhD, DACVCP, DACAW, DECAWSEL, Professor and Head of the College of Veterinary Medicine’s Department of Anatomy & Physiology, recently developed estimates for economic evaluation of available control options.
Below is a table I compiled for presentation at the K-State Anaplasmosis Day earlier this year with projected estimates of the cost of three anaplasmosis control strategies for a hypothetical herd of 100 cows. These calculations are based on ranges for the cost of medicated mineral ($0.13 - $0.55/head/day), vaccination ($8-$10/individual dose or $16-$20 for the primary and booster) and serological testing ($6-$9/head depending on which VDL you use, with a $2/head sample collection and processing fee).
The actual dollar figure will likely vary based on your location. Assuming that your producer is willing to blood sample their entire herd and pay for testing, knowledge of the seroprevalence of individual animals could allow implementation of a single or combinations of the following control strategies based on the overall production goals of the rancher:
- Targeted culling of positive cattle if the herd goal is disease eradication. These are typically seedstock producers or producers in non-endemic areas with a relatively low prevalence of disease.
- Targeted chemosterilization of positive cattle with oxytetracycline injections or imidocarb dipropionate. This is a strategy typically adopted by seedstock producers for high genetic merit cattle or for those “special” cows or herd bulls.
- Targeted and strategic feeding of CTC to control active infections. This assumes that mineral consumption will be consistent during the feeding period.
- Targeted vaccination of only negative cattle. In the absence of data to support vaccination, I am reluctant to recommend this course of action, but because testing is cheaper than the cost of the vaccine, only vaccinating negative cows may be more cost effective for a producer than blanket vaccination over several years.
It is important to recognize that anaplasmosis control programs that are predicated on the outcome of serological testing are based on the following 5 assumptions:
- Seropositive cows are persistently infected anaplasmosis carrier cows that are immune to reinfection. We believe that these cows may die from clinical disease if they are immunosuppressed and unable to control the emergence of new antigenic variants, but in general, these animals will likely not benefit from vaccination or CTC therapy once they recover from acute infection and the carrier state has become established.
- The cELISA test for anaplasmosis is reliable. We know that in low prevalence areas, the test may cross-react with maltose-binding peptide in the serum of approximately 40% of healthy cattle but the test is typically considered to have a greater than 90% specificity and sensitivity in most herds. We typically recommend following up with targeted individual or pooled PCR testing if the risk of a false-negative (resulting in disease persistence in the herd) or a false-positive (resulting in culling of a high dollar animal) would have significant consequence for the producer.
- Calves under 6 month of age may have circulating maternal antibodies or may be disease positive following in-utero infection and should be retested using either the cELISA test the following year or using an individual or pooled PCR test.
- The producer maintains a closed herd and commits to testing all incoming animals.
- The producer practices good biosecurity to minimize disease introduction and iatrogenic disease transmission through contaminated equipment during processing and vaccination.
Similarly, anaplasmosis control programs based on vaccination assume that the vaccine is effective and control programs based on CTC assume that intakes will be adequate and consistent across the herd and that the infection is susceptible to CTC. Unfortunately there are no perfect option available but in my opinion, knowledge of the herd disease status prior to implementing a disease control program is the most science-based approach available at this time.
For more on anaplasmosis, see these articles from BovineVetOnline: