Determination of Amblyomma tick distribution in Murehwa District, Zimbabwe, post land reform

M Dhliwayo and G Matondi*

Department of Animal Science, Faculty of Agriculture and Environmental Science, Bindura University of Science Education, Zimbabwe
marshalldhliwayo@yahoo.com
* Department of Animal Science, Women University in Africa, Zimbabwe
gospelmatondi@gmail.com

Abstract

The study was conducted to determine the occurrence of Amblyomma tick in Murehwa District. A total of 1800 cattle were sampled from 12 dip tanks randomly selected from 4 blocks of the district. The Amblyomma tick was found to be present in the district, but restricted to the Southern part, which is Musami area. Even within Musami the tick was found only at two dip tanks.

It is likely the Amblyomma tick drifted into Murehwa District as people relocated their cattle during and after the land redistribution exercise from other districts, especially the Southern Low-veld where the tick is prevalent. The fact that other areas in the district did not record the presence of the tick can be attributed to the characteristic micro-climatic conditions of Musami which typifies Southern Eastern Low-veld, which receives low rainfall and experience high temperatures, conditions ideal for Amblyomma survival.

Keywords: communal cattle, Heart water, resettled farmers, tick borne

Introduction

Zimbabwe has had one of the best veterinary services in Southern Africa which enabled it to win the European Market for the greater part of the period up to year 2000. However since 1998 there had been a decline in Veterinary and livestock support services, especially for smallholder farmers, attributed to dwindling budgetary allocation towards this department by the Ministry of Finance (Department of Veterinary Services 2004). With the collapse of the dipping program in the country cases of tick-borne diseases such as babesiosis, anaplasmosis, theileriosis and cowdriosis have been on the rise (Department of Veterinary Services 2003).

One of the greatest challenges farmers have faced is the ever rising mortalities due to tick-borne diseases (Monning and Veldman 1982). Surveys that were carried out in the early 1980s showed that communal cattle had acquired enzootic stability to tick-borne diseases (Norval 1989); however subsequent serological surveys indicated some reversion to endemic instability in some communal cattle (Katsande et al 1999). About 10,000 cattle die per annum due to tick borne diseases (Department of Veterinary Services 2003).  

Heart water is one of the major tick-borne diseases in Southern Africa which is transmitted by a tick known as Amblyomma hebraeum (Bruijin 1993a and b). The tick (Amblyomma hebraeum) has been reported to be present in Southern parts of Zimbabwe (Perry et al 1997).

Nationwide tick surveys conducted from 1980 and covering over 274 localities revealed that Ambylomma ticks were restricted to the South Eastern part of the country (Norval 1983). However, in a nationwide survey conducted by Mazhou and others (unpublished) in 1995, covering 3712 dipping tanks in both communal and commercial sectors revealed that the Amblyomma hebraeum was fast approaching the Highveld, a traditionally Amblyomma hebraeum-free area. Of late Amblyomma ticks have been reported in Murehwa district, a traditional Amblyomma hebraeum-free area. This has been accompanied by a rise in the number of animals dying of suspected heartwater in the district. It has been hypothesized that with the advent of the land reform program and the subsequent movement of livestock that occurred amidst poor veterinary services and controls, it is possible that animals infested with Amblyomma ticks entered the District. Therefore the general aim of this project was to determine the status of Murehwa district in terms of Amblyomma hebraeum infestation. 

Objectives:

The specific objectives of this study were to determine;

• The frequency of species of ticks present in the district

• The distribution of tick species across different health centres in the district

Methodology

Study area

The study was conducted in Murehwa district which is located 80km North East of Harare, the capital city of Zimbabwe. Murehwa district falls under Natural Region 2 which receives an average annual rainfall of over 750mm and experience temperatures averaging about 18 degrees Celsius in winter. Murehwa belongs to the Highveld and the major farming activities are intensive crop and livestock production. Some of the crops grown include maize, soya bean, potatoes and wheat. The major livestock activities include pig production, poultry, beef and dairy production. Murehwa district has seen a shift in farm ownership patterns from large farms owned by a few to many smaller plots benefitting more farmers. The new farmers came from various parts of the country and this happened at a time when controls for animal movements where difficult to manage as a result creating an opportunity for disease and parasite transfer between traditionally controlled areas. The major tick control method has been through acaricide application in dip tanks and the general practise has been to practise weekly dippings but due to financial constraints this has not always been the case. The breeds of cattle in Murehwa are best described as non descript as both the indigenous and exotic cattle exist and there has been no control over breeding practises such that the present animals are random crosses of the various breeds present in the area which include the indigenous Mashona and the exotic Brahman, Angus, and many others.  

Sampling design

The district was divided into four already existing animal health management blocks namely; Musami, Dombwe, Murewa and Ngwerume, each with 10 community dip tanks. Three dip tanks were randomly selected per each block and the systematic random sampling method was used to randomly choose animals, with every 20^th animal along the race being selected into the study sample. A sample size of about 80 animals was targeted per each dip tank and the sampled animal was marked with ink for identification. Two samples per dip tank separated by one week such that the final study sample consisted of 1800 selected animals. Table 1.0 shows the dip tanks chosen under each Animal Health Management Centre (AHMC).

Tick counts

For each sampled animal the tick species and their frequency were recorded. Animals were selected in the race just before entering the deep tank. The selected animals where diverted into a crash pen to allow for whole body collection of ticks according to the method of Londt et al., (1979). In places where there where no crashes proper restraint was employed to ensure safety of the personnel as well as comfort of the animal, such as use of ropes. Whole body collections were done and the collected specimen were placed in bottles and vials containing 6% formalin which were immediately labelled once the collection from each animal body was finished. The label showed the name of the dip tank, date and animal identification number. All collections were done in mid August to early September, a period when the environmental conditions were relatively dry and daily temperatures averaging about 24 degrees Celsius. The samples where then transferred to the Central Veterinary Laboratory for identification. The tick samples were counted and species were identified using hand lens and microscopes. Identification was done based on morphological and structural differences of the species and different instars. The classification of the ticks into their species was made according to the methods developed by Keirans and Robbins (1999) and Horak et al. (2002).  

Statistical Analysis

Tick count data, or tick load, from each sampled animal was transformed by the natural logarithms to base 10 before subjected to statistical analysis. The transformed data was then analysed using General Linear Model (GLM) procedure of SAS (1996) statistical package. The model used was:

Y = μ + A + D + E

Where,

Y = log10 of tick count

μ = overall mean

A = effect due to AHMC

D = effect due to Dip tank

E = random error 

Results

Table 2.0 is a presentation of the different tick species identified in the study area and their mean distribution across the 4 animal health and management centres. All the tick count data presented hereafter was subjected to log base 10 transformations.  Four tick species were identified; however the Amblyomma ticks were present only in one AHMC, namely Musami. Within the Musami AHMC, the Ambylomma tick was present in two of the three dip tanks chosen as shown in Figure 1.

Within Musami AHMC the Amblyomma tick was reported in two dip tanks, namely Chikwengera and Mt Pleasant. The other dip tank (Shamu) did not record any Amblyomma ticks. Many other tick species were recorded in all the four AHMC with the highest number of Boophilus decoloratus again being associated with Musami AHMC. Rhipicephalus appendiculatus was found to be uniformly distributed across the four AHMC. 

Discussion

This study revealed that Amblyomma ticks are present in Murehwa district though they are still confined to one block (AHMC). This is in agreement with the findings by Mazhou et al (1995), unpublished data, who reported that Amblyomma has in recent years drifted into the Highveld which was traditionally Amblyomma free. It is likely the Amblyomma ticks could have slowly drifted from the Southern Low-veld and with the advent of land reform and subsequent livestock movement tick distribution was exacerbated. The fact that the Amblyomma is still confined to one block may reveal the source of the tick as Musami area (the affected area) borders newly resettled farms. Resettled farmers from Buhera district where Amblyomma has been known to be present could have moved tick infested cattle. In addition a significant number of the newly resettled farmers at Mt Pleasant dip tank came from the South Eastern Lowveld, the main source of the Amblyomma ticks in the country. This was further compounded by the fact that relocation to resettlement areas coincided with the time when the dipping programme in Zimbabwe was collapsing. Historically Zimbabwe has had a tradition of intensive weekly dipping of cattle in communal areas to control tick borne diseases (Lawrence et al 1980) but economic hardships have affected the dipping of communal cattle (Perry et al 1990). 

Micro-climatic factors may also have played a role in the survival and establishment of Amblyomma in the Musami area. Although Musami is under natural region 2b, it has a micro-climate that is characterised by relatively low rainfall pattern and high temperatures compared to surrounding areas which receive high rainfall of about 750mm per annum. This could explain why spreading to neighbouring areas has not occurred. Amblyomma ticks strive in hot dry areas (Koch 1983), hence the perennial water shortages in Chikwengera, which had the highest Amblyomma tick counts, could have provided a conducive environment for the ticks. There is still a possibility though of the Amblyomma ticks spreading to other areas of Murehwa hence a need to keep surveillance in the district periodically.

Hyaloma tick and Boophilus tick distribution seem to be uniformly distributed across the whole district suggesting that this may portray the dipping protocol in the area which is erratic. The presence of Rhipicephalus in small numbers may depict the time of the year when the samples were collected since the tick`s activity is greatly reduced during drier times of the year (Moning and Veldman 1982).  

Conclusions

• It can therefore be concluded from this study that Amblyomma is now present in some parts of Murehwa district especially the Southern parts of the district. A greater part of the district is however still free of Amblyomma. Periodic surveillance and monitoring should therefore be done to reduce the spread of the ticks into the current free areas. There is also need to resuscitate the dipping programme in communal areas if the spread of tick borne diseases like cowdriosis is to be reduced.   It is also possible that the Amblyomma tick might have mutated in order for it to copy with Highveld conditions, as a result further studies are recommended to establish why and how the tick is coping with Highveld conditions.      

Acknowledgements

The authors acknowledge the support of several people and institutions who gave their support towards the success of this project. First acknowledge is Dr B. Mafuvadze, and Mr Mazhou for their guidance through out the research. VLT Mhlanga and Pambireyi, of Murehwa District gave immense technical and logistic support in sample collects across the whole district. Material support, in terms of bottles, labels and other important items were provided by The Central Veterinary Laboratory, to whom we are sincerely indebted.

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Received 21 March 2012; Accepted 10 June 2012; Published 1 July 2012

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