Effect of extrinsic incubation temperature on transstadial and transovarial transmission of Borrelia sp. in Ornithodoros (O.) savignyi and infectivity to vertebrate host.

Abstract

Effects of three extrinsic incubation (EI) temperatures on vector competence of Ornithodoros savignyi to Borrelia sp. isolated from a natural population of the tick in Egypt were investigated. The EI temperature influenced the efficiency of Borrelia sp. transmission by the female O. savignyi to hamsters. An EI temperature for 27 o C was optimum for successful transmission of Borrelia sp. where the highest infection rates (IRs) in hamsters occurred. Generally, the IRs in hamsters decreased by lowering the EI temperature to 17 o C or rising it to 37 o C in each of the corresponding experimental cases (number and postinfection period of the tick feeding per hamster) tested. Ornithodoros savignyi kept at 27 o C and 37 o C maintained borrelial infection transstadially from nymph 1 to 7 and adults. The transstadially infected stages transmitted the spirochetes to hamsters with higher IRs at 27 o C than 37 o C. Transovarial transmission of Borrelia sp. occurred during the first and second (at higher rates) gonadotrophic cycle in the infected female ticks kept at 27 o C and 37 o C. However, no molting or oviposition occurred at 17 o C.

Vector Competence of Five Ixodid Tick Species in Egypt for Borrelia

“…Generally, female ticks were more efficient than males and adults than immatures in transmitting borrelial infection as lower numbers of these life stages are required to produce similar or higher levels of infectivity to the rabbit fed upon by each species. The present results agree with those of previous investigators of other ixodids (Piesman & Sinsky, 1988) and argasid ticks (Shanbaky and Helmy 2000) Those authors found that the efficiency of transmitting Borrelia in ticks had increased by increasing the number of infected ticks per host animal, apparently the feeding of a larger number of infected ticks inoculates the host animal with a bigger number of spirochetes than the feeding of a smaller number. Lane et al, (1994) found that the plasma antibody titer of B. burgdorferi increased from 1.128 to 1.256 in mice exposed to feeding by one and two infected nymphs, respectively in I. pacicicus.…”

“…The observed higher percentages of borrelial infection in the laboratory than in nature might be attributed to the relatively optimum conditions of survival offered to the tick and pathogen in the laboratory versus the challenging and varied conditions in nature as environmental temperature, humidity, vertebrate hosts kinds, availability etc. which have been found to affect different physiological processes and interrelationships in both organisms (Schwan et al, 1995;Shanbaky et al, 2009;Wallace et al, 2019).…”

“…The high percentages of the frequency and efficiency of Rhipicephalus annulatus followed by H. dromedarii and H. excavatum in the acquisition, and maintenance of transmission of their natural Borrelia (e) proved the capacities of these tick species to serve as reservoirs and vectors of Borrelia (Hoogstraal 1985, Eisen et al, 2020 in Egypt. Also, the high levels of parameters such as Tst and Tov transfer of Borrelia in the tick life stages and generations, respectively, and transmission to the vertebrate host might reflect tick specificity for its natural Borrelia species (Hoogstraal, 1985 andHelmy 2000). On the other hand, H. anatolicum and H. impeltatum life stages showed the ability to acquire Borrelia isolated from their corresponding natural populations but generally failed to transstadially and transovarially maintain the infection till adult stage and next generations and only infected field-collected adult ticks transmitted their Borrelia with the lowest percent to rabbits fed upon in laboratory.…”