Distribution trends of bovine Anaplasma marginale in Iowa, based upon veterinary diagnostic lab submissions from 2017-2022

Anaplasma marginale is the common etiological agent of bovine anaplasmosis. Infection results in erythrocyte de­struction leading to the clinical signs of anemia, hypoxia, abortion, jaundice and sudden death. Cattle that survive this acute phase or have lower levels of initial bacteremia become chronic, persistent carriers. Carrier animals serve as reser­voirs for the organism and allow infection to spread via me­chanical or biological vectors, to susceptible herdmates. The objective of this study was to report the distribution trends of A. marginale positive test results during a 5-year period in Iowa. This study evaluated Iowa State University Veterinary Diagnostic Lab (ISU VDL) testing results from bovine cases submitted from January 1, 2017 to January 1, 2022, for molecu­lar and serological detection of all stages of anaplasmosis. Cattle residing in Iowa with positive results for PCR or com­petitive ELISA were included in the analysis. The state was divided into 4 geographical districts (1 = northeast, 2 = south­east, 3 = southwest, and 4 = northwest) and the number of pos­itive tests in each district was determined. Total positive tests by district included: northeast 282; southeast 277; southwest 223; northwest 281. Disease spatial analysis mapping, based upon geographic longitude and latitude location of herds with positive diagnostic tests, illustrate progressive disease expan­sion from the southern counties of Iowa, near the Missouri border, into the northern parts of Iowa. These results suggest that A. marginale has developed a widespread distribution across the state of Iowa.