Field evidence for density-dependent facilitation amongst Ixodes ricinus ticks feeding on sheep

Abstract

Engorged Ixodes ricinus nymphs collected from sheep resident in an upland UK field site were significantly lighter than nymphs that engorged on previously tick-naïve sheep, indicating that site-resident sheep continually exposed to ticks acquired anti-tick resistance. The weights of engorged nymphs that fed on naturally tick-resistant sheep increased significantly, however, when increasingly high numbers of adult female ticks fed on the sheep during seasonal peaks of tick activity. This relationship was unaffected by variations in nymph weight amongst individual sheep, between seasons and years, and potential effects of sheep infection with Ehrlichia phagocytophila; this suggests that high adult tick infestations may directly inhibit the expression of acquired anti-tick resistance by sheep. The length, width and weight of adult ticks and the scutum length of adult females were linearly related to their weight as an engorged nymph. The mean scutum length of adult female ticks feeding on sheep in the field site was greater than that of adult females obtained from engorged nymphs collected from sheep of the same site. This suggests that larger ticks have a survival advantage and that I. ricinus ticks exhibit density-dependent intraspecific facilitation at high infestation levels with potential consequences for the transmission of tick-borne diseases.

Seasonal incidence of parasitic diseases in bovines of south western Gujarat (Junagadh), India

“…Bovine anaplasmosis, caused by A. marginale, is an important rickettsial disease, transmitted to cattle biologically by ticks and mechanically by biting flies and blood contaminated fomites causing significant economic losses in tropical and subtropical areas of world (Ruybal et al 2009). However, the prevalence depends largely on the distribution and density of the reservoir hosts and tick vectors (Ogden et al 2002). In the present study, examination of Giemsa stained peripheral thin blood smears revealed 1.2 % animals positive for the inclusion bodies of A. marginale.…”

Prevalence and asssessment of risk factors for haemoprotozoan infectionsin cattle and buffaloes of South-West Gujarat, India

“…In the present study, highest incidence of B. bigemina infection was recorded in both cattle and buffaloes. The prevalence depends largely on the distribution and density of the reservoir hosts season and vectors (Singh et al, 2000;Ogden et al, 2002).The higher prevalence of bovine babesiosis can be closely correlated to the seasonal abundance of the vector Rhipicephalus microplus (Singh et al, 2000). The lower prevalence of theileriosis in bovines may be due to the lower occurrence of vector Hyalomma anatolicum anatolicum in this geographical part of the country.…”

Molecular and serological evidence of Anaplasma phagocytophilum infection of farm animals in the Black Sea Region of Turkey

“…However, the geographic distribution largely depends on the distribution and density of the tick vectors (Ogden et al, 2002). The rate of infection has been reported to be variable between countries and it may vary considerably even between neighbouring farms (Stuen et al, 2002).…”

“…Migrating birds could also potentially play a role in dispersing Ehrlichia by carrying infected ticks from one country to another (Bjoersdorff et al, 2001). However, geographic distribution is largely dependent on the distribution and density of the tick vectors (Ogden et al, 2002).…”