Anaplasma species surveillance in livestock and deer associated ticks from Northwest Arkansas

Despite an increasing seroprevalence of bovine anaplasmosis in Arkansas beef herds, little is understood about the bovine anaplasmosis transmission cycle in Arkansas. Bovine anaplasmosis, primarily transmitted by Dermacentor species, is caused by Anaplasma marginale. In Arkansas, tick collections from cattle are dominated by Ambylomma americanum, which is not associated with Anaplasma transmission, while D. variabilis and I. scapularis are collected in smaller numbers. Past studies may not fully account for the impact of I. scapularis in A. marginale transmission since these collections have typically been in the summer instead of during the peak activity levels of I. scapularis.

To assess the role of tick species in A. marginale transmission in Arkansas, we tested ticks collected from March 2020 to December 2021 for Anaplasma spp. A total of 3,506 ticks were collected from cattle, deer, and pastures. A. americanum was the most collected species, representing over 98% of cattle collections in 2020 and 2021. Initial testing determined cattle collected ticks that tested positive for Anaplasmataceae were negative for A. marginale. I. scapularis were collected from cattle during the early spring, but were negative for Anaplasmataceae. Conversely, I. scapularis was the dominant tick species (60.5%) on hunter-killed deer in 2021. A small number of A. americanum were also collected from the hunter-killed deer, but they were negative for Anaplasmataceae. Sequencing of Anaplasmataceae-positive individuals from all collection types is ongoing.

These results in combination with producer survey data indicate that ticks may not be the primary driver of A. marginale transmission in Arkansas.