Modelling the distribution of Rhipicephalus microplus and R. decoloratus in Zimbabwe.

Species distribution modelling is a very useful tool in vector management. Ticks are vectors of various pathogens which cause serious problems in livestock production in tropical countries. They have a high dispersal potential which is mainly facilitated by the movement of animals from one area to another. In light of the observed geographic expansion of Rhipicephalus microplus in Zimbabwe, we used species distribution modelling techniques to identify areas which may provide suitable habitats for the occurrence of this invasive tick species as well as the autochthonous Rhipicephalus decoloratus. Our results suggest that, despite the geographic expansion of R. microplus, climate will continue to be a limiting factor for the further expansion of this tick species. We expect its distribution to be restricted to the most favourable areas in the eastern and northern parts. The greater part of Zimbabwe is suitable for R. decoloratus, although in areas where R. microplus occurs, displacement of the former by the latter will be expected to occur. A heterogeneous climate, unregulated movement of cattle and episodic droughts are suggested to be possible factors for the continued existence of R. microplus and R. decoloratus in Zimbabwe and the partial displacement.

Shifts in the distribution of ixodid ticks parasitizing cattle in Zimbabwe.

In an attempt to update information on the ecological distribution of ixodid ticks (Ixodida: Ixodidae) in Zimbabwe, a cross-sectional survey was carried out between September 2013 and May 2015 at 322 dip tanks. A total of 15 tick species were collected, namely: Amblyomma hebraeum Koch (65.2%, n = 210/322), Amblyomma variegatum Fabricius (14.9%, n = 48/322), Hyalomma rufipes Koch (62.4%, n = 201/322), Hyalomma truncatum Koch (37.9%, n = 122/322), Rhipicephalus appendiculatus Neumann (60.6%, n = 195/322), Rhipicephalus compositus Neumann (0.3%, n = 1/322,), Rhipicephalus decoloratus Koch (61.8%, n = 199/322), Rhipicephalus evertsi evertsi Neumann (65.2%, n = 210/322), Rhipicephalus lunulatus Neumann (4%, n = 13/322), Rhipicephalus microplus Canestrini (32%, n = 103/322), Rhipicephalus near punctatus Walker and Horak (7.1%, n = 23/322), Rhipicephalus simus Koch (5.6%, n = 18/322) and Rhipicephalus cf. turanicus Pomerantsev (3.4%, n = 11/322). Compared with previous surveys, changes in the distribution of A. hebraeum, A. variegatum and R. microplus were recorded. The distributions of other tick species have largely remained unchanged. Factors which might have influenced these changes and the possible impacts on the epidemiology of tick-borne diseases are discussed.

The effect of treatment with a 1% injectable formulation of moxidectin during the rainy season and at the beginning of the dry season on gastrointestinal nematodes in cattle from communal areas in Zimbabwe.

The effect of 1% moxidectin/cydectin at 0.2 mg/kg live weight on gastrointestinal nematodes and on the growth of calves, weaners and cows was investigated in five communal areas on the highveld of Zimbabwe. Three field experiments were carried out between March 1996 and June 1997. In experiment 1, treatment was administered in all five areas at the end of the rainy season in March 1996, followed by a further treatment at the beginning of the dry season in May/June 1996. In experiment 2, the treatment was administered in three areas at the end of the rainy season in March 1997. In experiment 3, treatment was administcred in one area at the beginning of the dry season in April 1997. Large numbers of eggs were present in the faeces of calves and weaners at the start of experiments 1 and 2. Epg values were lower in cows and in all age categories in experiment 3. There was a statistically significant reduction in epg values in calves, weaners and cows following treatment with a reduction of 90-99% in all cases except in cows in experiment 3, where no meaningful assessment was possible owing to the low egg counts in both the treated and control cows. The dominating larval types in faecal cultures were Cooperia and Haemonchus. Trichostrongylus, Oesophagostomum and Bunostomum were also found. Following treatment, Haemonchus was suppressed far more than Cooperia. This may be related to a longer residual effect against abomasal parasites like Haemonchus in comparison to small intestinal worms like Cooperia. Anthelmintic treatment conferred significant weight gain advantages (p < 0.05) on treated calves. weaners and cows. The weight gains are discussed in relation to disease and nutrition.

The epidemiology of gastrointestinal nematode infections in communal cattle and commercial beef cattle on the highveld of Zimbabwe.

An epidemiological study of gastrointestinal nematode infections of cattle was conducted on the highveld of Zimbabwe from June 1993 to May 1995. The study was carried out in two communal areas, two conventional beef farms and two commercial beef farms with irrigated pastures. On all farms/areas, faecal egg counts were low (< 500 eggs per g faeces) during the dry season. During the rainy season faecal egg counts were highest in communal areas and lowest in conventional beef farms. Those of irrigated farms had intermediate values. During the dry season pasture larval counts were low in irrigated pastures and conventional beef farms and virtually zero in communal areas. They increased and peaked during the rainy season, coinciding with the egg count peaks. Worm burdens of necropsied cattle indicated that 100% of the animals were infected with nematodes. The important species were Cooperia pectinata, C. punctata, Haemonchus placei, Trichostrongylus axei and Oesophagostomum radiatum in all farms/areas and Ostertagia ostertagi in a beef farm with irrigated pastures. Haemonchus survived the dry season as inhibited early fourth stage larvae whereas Cooperia and Trichostrongylus survived as adults.

Bovine humoral immune responses to Haemonchus placei excretory secretory antigens.

The immune response of calves against excretory secretory (ES) products of adult Haemonchus placei was studied. The ES products of adult H. placei comprise at least ten polypeptides with molecular weights ranging from 10 to over 100 kDa. A primary infection of calves with H. placei did not result in a marked elevation of IgG serum antibodies reactive to ES antigens as demonstrated by ELISA. Immunoblotting experiments revealed that sera of primary infected calves recognised a 50 kDa antigen in most cases. An increase in the level of serum IgG antibodies was observed after trickle infections. The secondary immune response coincided with the recognition of a group of three ES antigens of around 50-55 kDa and one protein with a molecular weight of 24 kDa.