Prevalence of bovine trypanosomosis in Central Mozambique from 2002 to 2005

SPECHT, E.J.K. 2008. Distribution of bovine trypanosomosis in central Mozambique from 2002 to 2005. Onderstepoort Journal of Veterinary Research, 75:73–81 The study is the result of analyzing 16 895 blood smears of cattle collected at 180 sites in the provinces of Manica, Sofala, Zambézia and Tete in Mozambique. Of the blood smears 73.9 % were from Manica, 11.8 % from Tete, 8.5 % from Sofala and 5.8 % from Zambézia; 75.6 % of these were collected from smallholder cattle. Infections with trypanosomes were highest in smallholder cattle from Sofala Province with 36.8 % of the 872 blood smears examined positive for trypanosomes, and lowest in cattle of commercial farmers in Manica Province with only 6.2 % of 2 252 blood smears being positive. Trypanosoma congolense was the predominant species, followed by Trypanosoma vivax and Trypanosoma brucei sensu lato. Trypanosoma brucei, which also infects humans, was more frequent in the districts of Buzi, Mutarara and Morrumbala with 15.1 %, 10.5 % and 9.8 % of all examined cattle in 2005 being infected with it, respectively. The results show a significant increase in the infection rate with trypanosomes compared with results obtained in previous years by the Regional Veterinary Laboratory in Manica Province and by the Regional Tsetse and Trypanosomiasis Control Programme in Zambézia, Tete and Sofala provinces.


INTRODUCTION
Infections with trypanosomes represent one of the major constraints for cattle production in Mozambique because approximately two thirds of the country is infested by its vector, Glossina spp. (Pires 1952, Regional Tsetse andTrypanosomiasis Control Programme 2000). Infection results in anaemia, stunted growth, mass loss, reproductive disorders, poor milk production and if not treated, death. Smallholderswithout the knowledge and often the financial means to buy therapeutic agents-are most severely stricken by disease or death of the few cattle they possess. The disease deprives them of meat, sometimes milk and draft power.
During the colonial period cattle husbandry was absent in large areas in central and northern Mozam bique (Pires 1952). These areas are part of the "common fly belt", which extends over some 320 000 km² in Malawi, Mozambique, Zambia and Zimbabwe. Little information exists about tsetse fly eradication programmes during colonial times. Between 1962Between -1975 control operations against Glossina morsitans and Glossina pallidipes were carried out in Muabsa and Rio Save areas, using Dieldrin until 1969 and DDT thereafter (Lovemore 1986). In 1985 a 15-year programme for tsetse fly and trypano somosis control was proposed for the "common fly belt" (Jordan 1985). This Regional Tsetse and Trypanosomiasis Control Programme (RTTCP) conducted a survey in 46 districts of the ten provinces between May 1995 and February 2000 to update the information about distribution of bovine trypanosomosis in Mozambique. The Regional Veterinary Laboratory (LRV) in Chimoio carried out several surveys on trypanosomosis in smallholder cattle in the Manica district of Manica Province (Specht 1999a(Specht , 2001(Specht , 2003.
The lack of control implementation after independence, movement of people and cattle, climatic changes during the last 15 years with a drought at the beginning of the 1990s, and the abandoning of farm land after the heavy rains in 2000 undoubtedly had a marked influence on the distribution of the tsetse fly and trypanosomosis. Bovine trypanosomosis is also on the increase because of the distribution of cattle to smallholders in areas known to be tsetse fly habitats, often without training the farmers in cattle husbandry.
The purpose of this paper is to provide information pertaining to the distribution of bovine trypanosomosis in 23 districts of the provinces of Manica, Sofala, Zambézia and Tete that will assist the veterinary authority in the effort to fight the disease.

Sampling sites and sample selection
During the last 4 years the LRV in Chimoio in Manica Province has assisted not only the veterinary services of this province, but also those of Sofala, Zambézia and Tete provinces which possess only small veterinary laboratories (Fig. 1). The veterinary services urgently needed an update on the disease situation in smallholder cattle, since the state had stopped subsidizing basic animal health care some years ago and the smallholders did not take care of their animals as expected. Nowadays most of the smallholders seek treatment only for the very sick animals and regular treatments with trypanocides are only done by a few more educated smallholders.
Samples were taken from cattle at dip tanks and treatment crushes indicated by the services to determine the prevalence of blood and intestinal para- The sample size depended on the total cattle population at a particular site (especially at small commercial farms, the total cattle population did not exceed 50-60 animals), the appearance of smallholder's cattle at the sampling site (at some sites only 25-50 animals appeared) and the limits in the capacity of the laboratory staff to perform the in vivo examination for trypanosomes at the site. Therefore, generally a maximum of 72 cattle per site could be sampled. The number of the smallholder cattle existing at a particular site chosen by the distrital veterinary officer was often not known before the start of the sampling. But varied mostly between 300 and 1 500 animals and 5-25 % of this cattle population was being sampled. During collection of samples from smallholder cattle, care was taken to sample cattle of most of the smallholders present at the sampling site. Generally the worst and the best farmers, which did not care to participate, may be underrepresented during the sampling.
At commercial farms 25-90 % of the cattle population were being sampled.

Parasitological diagnostic methods
Blood samples (two capillary tubes per animal) were taken from marginal ear veins into heparinised microhaematocrit tubes (Na-heparin haematocrit capillaries from Brand, Hirschmann or Herenz) and onto glass slides, as thin blood smears. The capillary After centrifugation the packed cell volume (PCV) was determined and the capillary tubes were rotated under the microscope in search of motile trypanosomes in the buffy-coat area using x 10 and x 20 objective lenses (Woo 1970). The thin smears were fixed with methanol, stained with Giemsa and observed under a 100x oil immersion lens. Fixation of the blood smears was generally done on site during sampling in Sofala, Zambézia and Tete provinces and in distant districts in Manica Province and at the Veterinary Laboratory in Chimoio for samples taken in the nearby Manica and Gondola districts. Staining with Giemsa was always done at the Veterinary Laboratory in Chimoio.  (Table 2).

DISCUSSION
Most of Mozambique north of the Save River with the exception of some highlands in Niassa, Cabo Delgado and Tete is considered to be infested by tsetse flies (RTTCP 2000). Historical data indicate that around 1950 large tsetse-infested areas of central Mozambique such as the districts of Gorongosa, Cheringoma and Chemba had no cattle at all. Others such as Mossurize, Machaze, Mocuba and Mopeia that now have large populations of cattle, had less than 500 animals at that time (Pires 1952). Most of these areas had good agro-ecological conditions for the grazing, and 40 years earlier they had harboured large herds, which disappeared due to trypanosomosis. A good example is provided by the districts of Chemba and Sena, which had about 15 000 head of cattle around 1913 (Pires 1952). Trypanosomosis was, apart from tuberculosis, considered the main constraint for animal husbandry along the banks of the Révuè River in Manica and Sofala Province (Gradil 1969).
Despite the lack of updated data about the distribution of the tsetse fly in central Mozambique and the consequent risk of the animals becoming infected with trypanosomes, in the decade after 1990 cattle were distributed on a large scale to smallholders. The population resettled at the end of the civil war needed animals, especially for traction purposes. The distribution was generally done without training the new owners in basic animal health care. At that time the provincial and district veterinary officers and dip tank attendants looked after the health of the animals and treated sick ones at no, or only very low cost to the owners. This policy changed about 5 years ago and the state stopped subsidizing basic animal health care services. The result was a large increase in parasitic diseases, including trypanosomosis (Specht 2003).
The LRV relies unfortunately until now on parasitological methods for the detection of trypanosomes, combining the observation of thin blood smears with the microhaematocrit centrifugation technique (WOO method). Both methods fail to detect all infected animals (Luckins 1993) and are dependant on the volume of blood examined and the experi-ence of the microscopist. The prevalence of trypanosomes would without doubt been higher if serological diagnostic tests would have been used. Connor (1993)  In Manica Province between 1989 and 1997 the LRV examined 21 660 head of cattle of which 7.7 % were positive for trypanosomes (Specht 1999b). In 1993 morbidity and mortality increased in cattle in Manica district and trypanosomal infections were found in 35.9 % of 585 cattle examined between January and May (Specht 1999a). After rigorous treatments trypanosomal infections were reduced to 7.7 % in 519 cattle examined between March and August of 1994 (Specht 1999b).
The encroachment of people and their livestock into tsetse-infested wilderness areas is considered to be responsible for the changes in the propagation of trypanosomosis (Van den Bossche 2001). Clearing of vegetation and the introduction of agriculture and animal husbandry lead to a gradual decrease in the density of wildlife and cattle become the main source of food for tsetse flies. This leads consequently to an increase in trypanosomal infections in cattle. This pattern is probably partly responsible for the high infections rates in smallholder cattle.  (Specht, unpublished data 2006).
Trypanosoma congolense was the predominant species during the RTTCP survey of 1995-2000 and also in smallholder cattle during the study carried out by the LRV in 2002-2005. Historically T. congolense was considered the epizootiologically more important species, but T. vivax, which was the predominant species on commercial farms in the LRV study, was found more frequently in domestic animals (Pires 1952).
In the present study T. brucei sensu lato accounts for 23.65 % of the infections (including mixed infections) in smallholder cattle and for 18.08 % of the infections in commercial cattle. This is alarming considering that T. brucei also infects humans, with game animals and livestock serving as the reservoir of infection (Kioy & Mattock 2005). In Uganda cattle are considered to be its principal reservoir (Fèvre et al. 2005). Fèvre, Picozzi, Waiswa, Coleman & Welburn (2005) observed that the movement of cattle into the Soroti district in Uganda in 1998 resulted in the spread of sleeping sickness to the area.
The PCV values in commercial cattle are generally higher than in smallholder cattle which are due to the regular dipping and treatments against blood and gastrointestinal parasites and to pasture management and feed supplementation during the dry season. The influence trypanosomal infection has on the PCV will be subject of a separate report. In particular, smallholder cattle often have a "cocktail" of infections, which makes it difficult to judge which one is more responsible for low PCVs. Further studies on trypanosomosis in which other PCV-influencing factors will be eliminated by treating the animals with babesicides and anthelminthics, will be carried out.
During their annual meeting held in Togo in 2000 the African Union heads of State adopted a decision to eradicate tsetse flies in Africa since they are a threat to human and animal health. They declared the year 2001 as "The Year of the Control of the Tsetse Fly" (Jihui 2001). In 2001 the Pan African Tsetse and Trypanosomosis Eradication Programme (PATTEC) was launched, but Mozambique has clearly not yet benefited from these decisions. Great efforts will be needed by government agencies, donors and also by PATTEC to deal with this situation which may, in addition, threaten neighbouring countries.