Transmission of Anaplasma marginale by unfed Rhipicephalus microplus tick larvae under experimental conditions

The current description of biological transmission of Anaplasma marginale by Rhipicephalus microplus ticks, includes of the biological intrastadial and transstadial transmission. Both transovarian transmission of Anaplasma from engorged ticks to their progeny and, transmission from infected unfed larvae to the mammalian host is controversial. In order to demonstrate vertical transmission of A. marginale by R. microplus ticks under experimental conditions, feed-acquisition infected engorged females were incubated at 18 degrees C or 28 degrees C for oviposition. Larvae hatched from these ticks were used to infest two steers for each incubation temperature. None of the four steers infested with either lot of larvae developed clinical disease, yet subclinical infection was observed in the steers infested with larvae from engorged ticks incubated at 28 degrees C for hatching. gDNA from, larvae used for the infection of the carrier tick donor, gDNA from larvae oviposited at 28 degrees C, gDNA from blood of A. marginale-positive steers, were positive for amplification of msp5 and msp1a the variable region by PCR. All other DNA samples from the original stabilate, blood from the donor steer, larvae from ticks incubated at 28 degrees C and blood from steers infested with these same larvae were positive to both, msp5 and msp1a PCR. msp1a sequences of all PCR products were the same and are consistent with previously reported Tlapacoyan-2 sequence. The present evidence indicates that R. microplus is capable of passing A. marginale to its progeny and that these infected larvae can transmit the infection to susceptible hosts.