Role of Rhipicephalus bursa larvae in transstadial transmission and endemicity of Babesia ovis in chronically infected sheep

Authors: RECEP, FIRAT - University Of Firat; MEHMET, CAN ULUCESME - University Of Firat; MUNIR, AKTAS - University Of Firat; ONUR, CEYLAN - Konya Technical University; FERDA, SEVINC - Konya Technical University; Bastos, Reginaldo; Suarez, Carlos; SEZAYI, OZUBEK - University Of Firat

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2024
Publication Date: 8/12/2024
Citation: Recep, F., Mehmet, C., Munir, A., Onur, C., Ferda, S., Bastos, R.G., Suarez, C.E., Sezayi, O. 2024. Role of Rhipicephalus bursa larvae in transstadial transmission and endemicity of Babesia ovis in chronically infected sheep. Frontiers in Cellular and Infection Microbiology. https://doi.org/10.3389/fcimb.2024.1428719.
DOI: https://doi.org/10.3389/fcimb.2024.1428719

Interpretive Summary: The hemoparasite Babesia ovis, transmitted by Rhipicephalus bursa ticks, causes significant clinical disease, characterized by fever, anemia, and high mortality in sheep. Despite the importance, there is currently a lack of comprehensive research on the transmission patterns and epidemiology of this parasite. Herein, we used an experimental model of infection to investigate whether sheep that survived babesiosis without treatment between May and July (Spring season), when cases of the disease occur, could serve as a source of infection for B. ovis-free host-seeking R. bursa larvae in November-December (Fall season). Results demonstrated transmission of B. ovis via blood inoculation from chronically infected donor to naïve sheep. However, despite the presence of B. ovis circulating in donor animals, the parasite load was insufficient to infect R. bursa larvae, and tick-infested recipient sheep remained uninfected throughout the study (100 days post-tick infestation). In conclusion, experimental evidence strongly suggests that sheep infected with B. ovis in the Spring season, recovering from the disease without treatment, do not likely serve as a source of infection for host-seeking R. bursa larvae in the Fall season.

Technical Abstract: Babesia ovis, particularly transmitted by Rhipicephalus bursa ticks, is the causative agent of ovine babesiosis, a significant disease characterized by fever, anemia, and hemoglobinuria, and high mortality in sheep. Despite the importance of ovine babesiosis, there is currently a lack of comprehensive research on the transmission patterns and factors impacting its epidemiology. In this study, we used an experimental model of infection to investigate whether sheep that survived babesiosis without treatment between May and July (Spring season), when cases of the disease occur, could serve as a source of infection for B. ovis-free host-seeking R. bursa larvae in November-December (Fall season). Thus, three donor sheepwere experimentally infected with B. ovis/Alacakaya stabilate, and after six months, persistence of B. ovis was assessed in vivo through blood and tick transmission experiments. For blood transmission, 100 ml of blood was collected from the donor animals after six months of infection and administered intravenously to three recipient sheep. Simultaneously, the donor sheep were experimentally infested with 0.1 gram of B. ovis-free R. bursa larvae. Ticks fed for repletion, molted to nymphs, and engorged nymphs were collected. Engorged nymphs were placed in an incubator to molt to unfed adults. Subsequently, additional three recipient sheep were experimentally infested with 50 unfed female and 50 unfed male R. bursa. Following blood and tick transmission, all recipient sheep (n=6) were monitored for the presence of B. ovis for 100 days using microscopic, serological, and molecular approaches. The molecular and serological analysis confirmed the presence of B. ovis in the three sheep that received blood from the donor animals, leading to clinical infection in two of them. However, despite the presence of B. ovis circulating in these animals, the parasite load was insufficient to infect R. bursa larvae, and all three-recipient sheep remained negative for B. ovis following infestation with ticks fed in the three infected donor sheep. In conclusion, experimental evidence strongly suggests that sheep infected with B. ovis in the Spring season, recovering from the disease without treatment, do not likely serve as a source of infection for host-seeking R. bursa larvae in the Fall season.