Tissue-specific localization of tick-borne pathogens in ticks collected from camels in Kenya: insights into vector competence.

Background: Tick-borne pathogen (TBP) surveillance studies often use whole-tick homogenates when inferring tick-pathogen associations. However, localized TBP infections within tick tissues (saliva, hemolymph, salivary glands, and midgut) can inform pathogen transmission mechanisms and are key to disentangling pathogen detection from vector competence. Methods: We screened 278 camel blood samples and 504 tick tissue samples derived from 126 camel ticks sampled in two Kenyan counties (Laikipia and Marsabit) for Anaplasma, Ehrlichia, Coxiella, Rickettsia, Theileria, and Babesia by PCR-HRM analysis. Results: Candidatus Anaplasma camelii infections were common in camels (91%), but absent in all samples from Rhipicephalus pulchellus, Amblyomma gemma, Hyalomma dromedarii, and Hyalomma rufipes ticks. We detected Ehrlichia ruminantium in all tissues of the four tick species, but Rickettsia aeschlimannii was only found in Hy. rufipes (all tissues). Rickettsia africae was highest in Am. gemma (62.5%), mainly in the hemolymph (45%) and less frequently in the midgut (27.5%) and lowest in Rh. pulchellus (29.4%), where midgut and hemolymph detection rates were 17.6% and 11.8%, respectively. Similarly, in Hy. dromedarii, R. africae was mainly detected in the midgut (41.7%) but was absent in the hemolymph. Rickettsia africae was not detected in Hy. rufipes. No Coxiella, Theileria, or Babesia spp. were detected in this study. Conclusions: The tissue-specific localization of R. africae, found mainly in the hemolymph of Am. gemma, is congruent with the role of this tick species as its transmission vector. Thus, occurrence of TBPs in the hemolymph could serve as a predictor of vector competence of TBP transmission, especially in comparison to detection rates in the midgut, from which they must cross tissue barriers to effectively replicate and disseminate across tick tissues. Further studies should focus on exploring the distribution of TBPs within tick tissues to enhance knowledge of TBP epidemiology and to distinguish competent vectors from dead-end hosts.

Emergence of the invasive malaria vector Anopheles stephensi in Khartoum State, Central Sudan.

The emergence of the Asian invasive malaria vector, Anopheles stephensi, has been identified in Khartoum, the capital city of Sudan. This is the first report that confirms the geographical expansion of this urban mosquito into Central Sudan. We urgently recommend the launch of a national entomological survey to determine the distribution of this invasive disease vector and to generate essential information about its bionomics and susceptibility to available malaria control measures.

Drop-off rhythms and survival of Hyalomma anatolicum (Acari: Ixodidae) fed on crossbred (Friesians x Zebu) calves in Sudan.

Hyalomma anatolicum is one of the most economically important ticks in the Sudan. It is the main vector of tropical theileriosis in cattle and other diseases in different species. The study aims to investigate the drop-off rhythms and survival periods of tick stages fed on crossbred calves. Larvae, nymphs and adults fed on crossbred calves (male, 3-6 months old, Friesians x Zebu) kept under zero grazing system. Drop-off rhythms of engorged stages were studied under field conditions while the survival periods of unfed stages were investigated under field and laboratory conditions (27 °C and 85% R.H.). Significantly high numbers of engorged larvae dropped at night between 20H:00 and 07H:00. (March, April and August). Engorged nymphs dropped late evening and early night 16H:00-20H:00. (September), while insignificant number of engorged females dropped between 10H:00 and 14H:00 (October). Survival durations of unfed H. anatolicum stages were longer under laboratory conditions than in the field. These were 99.36 ± 1.24 and 13.12 ± 0.68 days for larvae, 63 ± 1.33 and 16 ± 0.87 days for nymphs and 90 ± 3.6 and 45 ± 2.7 days for adults, respectively. Under field condition survival studies were conducted in May, August and December 2016 for larvae, March, May, August and December 2016 for nymphs and in October 2016 for Adults. In August, 70% of unfed larvae and nymphs survived for three weeks and 2.5 weeks, respectively, in May, 16% of unfed larvae survived for one week while no unfed nymphs survived for more than 4 days. This finding may indicate that larvae are more resistant to desiccation than nymphs. The abnormal changes on the alloscutum of H. anatolicum desiccated nymphs and females were observed being shrunken and truncated posteriorly, a finding which opens new avenues for further studies. For control strategies more studies are recommended on the dropping to allow ticks drop in an area not suitable for further development as one of the control strategies and the survival studies also is exploited in rotational grazing of animals.