Failure to Eliminate Persistent Anaplasma marginale Infection from Cattle Using Labeled Doses of Chlortetracycline and Oxytetracycline Antimicrobials

Abstract

Bovine anaplasmosis, caused by the intracellular rickettsial pathogen Anaplasma marginale, is the most prevalent tick-transmitted disease of cattle worldwide. In the U.S., tetracycline antimicrobials are commonly used to treat and control anaplasmosis. Oxytetracycline, administered by injection, is indicated for treatment of clinical anaplasmosis in beef and dairy cattle and calves. Chlortetracycline, administered orally, is indicated for control of active anaplasmosis infection in beef and nonlactating dairy cattle. Tetracyclines have been demonstrated to be effective for treating active anaplasmosis, but their ability to eliminate A. marginale at currently approved therapeutic doses or dosing regimens remains unclear. In the absence of approved dosing regimens for A. marginale clearance, a study was conducted to determine the effect of approved oxytetracycline and chlortetracycline indications on A. marginale bacteremia. Fifteen animals with persistent anaplasmosis were enrolled and divided into three treatment groups. Group 1 (n = 6) received oral chlortetracycline (1.1 mg/kg bodyweight) administered via hand-fed medicated feed for 60 consecutive days. Group 2 (n = 6) received injectable oxytetracycline administered subcutaneously at 19.8 mg/kg bodyweight three times in 3-week intervals. Group 3 (n = 3) served as an untreated control. After 60 days, bacteremia failed to permanently decrease in response to treatment. This result indicates that clearance of A. marginale is unlikely to be reliably achieved using currently approved tetracycline-based regimens to manage anaplasmosis.

Molecular prevalence of Anaplasma marginale and associated risk factors in beef cattle herds from Ohio: a cross-sectional study

“…Out of the 29 cattle from the Coshocton farm that had been treated about a month prior to sampling with oxytetracycline (1 to 3 doses), 25 of these were PCR positive for A marginale. Although a small sample size, these findings corroborate previous studies, [4][5][6] which suggest that antimicrobial therapy may not eliminate carriers. Therefore, carrier status after antimicrobial therapy should be scrutinized and not assumed.…”

“…1,3 This is especially important to consider because current recommendations for antimicrobial treatment may not eradicate infection, allowing for cattle to persist as chronic carriers. [4][5][6] Therefore, identifying carriers can help reduce disease transmission via surveillance-based interventions.…”

Comparative Study of the Use of Doxycycline and Oxytetracycline to Treat Anaplasmosis in Fattening Lambs

“…However. their ability to eliminate Anaplasma at currently approved therapeutic doses remains unclear [ 19 ]. For that reason, it was decided to apply this antibiotic to one of the analyzed groups.…”

RPA-CRISPR/Cas12a assay for the diagnosis of bovine Anaplasma marginale infection

“…The parasite is carried by blood-feeding insects such as ticks and flies, and bovines can contract the disease through insect bites or direct contact with traces of blood from infected animals 9 . The disease can be treated with extensive administration of tetracyclines although permanent clearance of the parasites remains questionable 10 – 12 .…”