Longitudinal and seasonal changes in the relative abundance of Amblyomma tick infestations in relation to the prevalence of heartwater (Ehrlichia ruminantium infection) in goats in the area of Mnisi (Mpumalanga), South Africa

Abstract

The present study was conceived with the main objective of establishing more insight in the epidemiology of heartwater and investigating the longitudinal and seasonal changes in the relative abundance of Amblyomma tick infestations on indigenous goats in the area of Mnisi (Mpumalanga), South Africa. One hundred eighty out of 184 goats examined for tick infestation in November 2013 were infested by ticks. Two Ixodid tick species were found, with Amblyomma hebraeum being the predominant tick encountered followed by Rhipicephalus (Boophilus) microplus. In total 2732 ticks were collected, of which the majority were immature ticks (557 adults, 1449 nymphs and 726 larvae). Compared to a previous study by F. van der Steen (2013), wherein collections were carried out during winter (June and July 2013), a substantial increase in the number of A. hebraeum adults was observed. The tick:goat ratio for A. hebraeum adults during November was 2.8:1 compared to 0.2:1 during June and July. A. hebraeum adults were present on goats in all villages and most numerous in the village of Share. R. (B.) microplus ticks were present on goats in small numbers. PCR and RLB assays were applied to study the prevalence of E. ruminantium infection in A. hebraeum ticks. The rates of infection ranged from 25% (17 out of 68) in A. hebraeum adults and 23,5% (4 out of 17) in pooled nymphal samples recovered from goats during November 2013 to 13% (3 out of 23) in adult A. hebraeum ticks and 11,8 % (2 out of 17) in pooled nymphal samples collected during June and July 2013 as reported by F. van der Steen (2013). Severe damage to feet, peri-anal region, udders and teats caused by the ticks was observed at 47 out of 53 households. The observed damage, infection rates of A. hebraeum and the fact that goats can act as important alternative hosts for cattle ticks underscore the necessity of including goats in tick control programmes designed for cattle at the same locality. The results of this study combined with a previous study by F. van der Steen (2013) and future studies can provide an important insight in the longitudinal and seasonal changes in the relative abundance of Amblyomma tick infestations in relation to the prevalence of heartwater in goats in the area of Mnisi. These insights can be used as a basis for the development of well-targeted tick control programmes.