Journal Article
Demonstration of Anaplasma marginale transmission to cattle through the intra-transstadial and by unfed larvae of Rhipicephalus microplus routes, with subsequent calculation of infection rates
Luciana Maffini Heller; Dina María Beltrán Zapa; Igor Maciel Lopes de Morais; Vanessa Ferreira Salvador; Luccas Lourenzzo Lima Lins Leal; Luiz Fellipe Monteiro Couto; Lídia Mendes de Aquino; Lucianne Cardoso Neves; Bianca Barbara Fonseca da Silva; Lorena Lopes Ferreira; Felipe da Silva Krawczak; Caio Marcio de Oliveira Monteiro; Welber Daniel Zanetti Lopes
Tropical Animal Health and Production · Vol. 58, Issue 5 · 2026
Abstract
The objective of this study was to assess the infection rate of Anaplasma marginale in cattle by Rhipicephalus microplus . Two experiments were conducted for this purpose. Experiment 1 evaluated the infection rate by the intrastadial and transstadial routes. Calves naturally infected with A. marginale were infested with R. microplus and were called “positive with ticks” (PWT). These PWT animals were housed together with A. marginale -negative, tick-free calves, called “negative and free-tick” (NFT) for 31 consecutive days. On day 31, the PWT animals were removed from the pens and returned to the farm/herd of origin. The NFT animals remained in the pens until day 84, and the possible infection rate of these calves with A. marginale by cattle ticks via the transstadial or intrastadial route was investigated (using blood smears, PCR, and ELISA). During this period, we evaluated the transfer rate of R. microplus from PWT to NFT animals. As a result of Experiment 1, only adult male and female ticks were found on the NFT animals. The transfer rate of ticks from PWTs to NFT calves was 0.10% (31/28464), and 70% (7 of 10), and all the NFT animals housed along with PWT animals became infected by A. marginale. In Experiment 2, the infection rate of A. marginale in calves by R. microplus larvae was carried out in two steps. The first step involved the use of the first tick generation larvae, which were used to infest (at 40,000 larvae per animal) five NFT calves. If any of these five NFT animals became infected with this rickettsia, fully engorged females detached from these animals were collected to perform the second step of the Experiment 2, conducted with the second-generation larvae. The second-generation larvae came from the first generation. Another five NFT calves were infested with 40,000 larvae/animal from the second tick generation. As a result of Experiment 2, 100% of NFT calves were infected by A. marginale due to infestation with R. microplus larvae of the first and second generations. This tick species has epidemiological importance in the transmission of A. marginale to calves by the intra-transstadial or unfed larval route.