Comparison of the transmission of Theileria parva between different instars of Rhipicephalus appendiculatus

Abstract

The transmission of Theileria parva by nymphal and adult Rhipicephalus appendiculatus was compared by the assessment of salivary gland infections in tick batches fed on the same group of infected cattle at the same time. When larval and nymphal R. appendiculatus Muguga ticks were fed concurrently on cattle undergoing acute infection with T. parva Muguga, the resultant nymphae developed a slightly lower prevalence of infection than did the adult ticks. The abundance of infection was 5-20 times higher in the adult ticks than in the nymphae. When larval and nymphal R. appendiculatus Muguga and R. appendiculatus McIlwaine were fed to repletion on cattle infected with T. parva Boleni, a parasite causing subacute infection, resultant adult tick batches had a relatively high prevalence of infection, but infection was not detected in resultant nymphal batches. When cattle that were carriers of 2 stocks of T. parva, Marikebuni and Kiambu 5, were used as the source of infection, the infections developing in adult R. appendiculatus Muguga ticks were much higher than those developing in nymphae. The structure of salivary glands differed between nymphal ticks, adult males and adult females, and this is considered to be an important factor affecting the infection levels. The morphology of the type III acini, the target acini for sporogony, was similar, but the mean numbers of type III acini were different, with 87 in nymphae, 1346 in males and 1736 in females. This difference was correlated with the different tick instars and sexes was similar, the rate of sporogony was fastest in feeding nymphae, taking on average 2-3 days. compared to 3-4 days in females and an irregular period in the males. These results are discussed in relation to the epidemiology of T. parva.

Investigations into the natural infection rate of Haemaphysalis qinghaiensis with Piroplasma using a nested PCR

“…Despite it having been reported that the female ticks may play a more important role in transmission than males (Ochanda et al 1996;Salih et al 2005), the development of Theileria parasites in vector ticks depends on several extrinsic and intrinsic factors (Sangwan et al 1989;Sayin et al 2003;Salih et al 2005). Our investigation did not reveal any diVerence between the pathogen-carrying ability of females and males, which is in agreement with the study of Aktas et al (2006).…”

Induction of humoral immune response to multiple recombinant Rhipicephalus appendiculatus antigens and their effect on tick feeding success and pathogen transmission

“…Theileria parva infection rates are highest in adult females they are considered the most important stage for acute disease transmission. Nymphal ticks have lower infection levels and are considered important for the transmission of sub clinical disease and as a parasite acquisition stage for adult ticks [28]. The effect of the vaccine focused on the ability of nymph and adult female ticks to successfully feed and for adult females to transmit T. parva .…”

Eradication and control of livestock ticks: biological, economic and social perspectives

“…Its peak of activity in the dry season is correlated with new infections with T. parva (Mulumba et al 2000) and this instar is an effective vector in which the low numbers of theilerial sporoblasts per nymph are probably compensated by the typical 10-fold greater number of nymphs compared to adults infesting cattle (Ochanda et al 1996(Ochanda et al , 2003. If the control of ECf is the priority for strategic control in southern Africa, where there is a distinct seasonal peak of R. appendiculatus nymphs, then this instar needs to be considered.…”