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African Animal Trypanosomiasis (AAT) is a parasitic disease that causes serious economic losses in livestock due to anaemia, loss of condition and severe emaciation (Connor, 1992; Steverding, 2008). The causal parasite belongs to genus Trypanosoma and is passed between different species of livestock and wild animals by tsetse flies. (Ikenna, 2008; Thumbi et al., 2010). The most common species associated with the disease in animals are Trypanosoma vivax T. congolense, T. brucei and T. Vivax (Onditi et al., 2007). The degree of infection can be influenced by factors such as animal immune status, different strains of trypanosome among others in both local and exotic breeds of cattle kept in many parts of Kenya (Steverding, 2008). The disease is a major restraint to livestock industry in many parts of Africa with a big population of cattle at risk while the annual losses have been reported to amounts to over US $ 1 billion (Murray and Gray 2002; Thumbi et al., 2010).
2.0 Epidemiology and prevalence
A study by Ikenna (2008) showed that large areas of Africa, approximately 4 million Km2 have been rendered unsuitable for livestock production by trypanosomes. In Kenya, the disease is more prevalent in the western part of the country particularly in Lambwe valley in Teso district Thumbi et al., (2008).
Studies have shown that in many parts of Africa, cattle are more susceptible to T. congolense (McDermott et al., 2003) but Thumbi et al., (2010) reported a trypanosome prevalence of 41% in Suba district in Kenya where T.vivax infections were most prevalent raising a lot of concern in the recent months. Similar findings were demonstrated by Karanja (2005) who recorded a high prevalence of T. vivax in Busia district in Kenya though the prevalence was lower than the current reported figures.
3.0 Economic impact
AAT constrains agricultural production in Kenya where some studies have reported increased preventive and treatment costs, reduced milk and meat production and poor conception rates (Swallow, 1999; Muriuki et al., 2005). Kristjanson et al., (1999) reported that majority of farmers were disappointed as they had to look for other alternatives to cultivate their land at the start of planting season as diseased oxen could not pull plough. Griffin and Allonby (2005) reported losses associated with poor weight gain and high mortality amounted to US $ 0.5 and US $1 per head for goats and sheep respectively while Wilson et al., (1986) showed that animals which were not on a 3 month prophylactic programme within a ranch had lost about 14% body weight.
4.0 Treatment and control strategies of AAT in Kenya
AAT is very difficult to control because the parasites are so widely distributed in the environment (Steverding, 2008; Van Den Bossche et al., 2010). However, a wide variety of tsetse control techniques have been developed and undergone trials in Kenya and other parts of africa (Kuzoe and Schofield, 2004; Thumbi et al., 2010). For a long period of time many trypanocidal drugs such as homidium bromide and diminazine diaceturate have been used for prophylaxis. However, drug resistance has been of great concern hence research has been going on to have breeds of cattle which can be immune to AAT (Holmes, 1997; Black et al., 2001; Thumbi et al., 2010). Initially, control of the vector was carried out using insecticides such as deltamethrin but with the ever increasing research there have been use of new technologies such as the biconical trap and baiting technology (Kuzoe and Schofield, 2004). Nevertheless, most of the control methods being employed raise environmental concerns since some result in air pollution, poisoning of other important flora and fauna thus the need for deeper research into control methods which will be less detrimental (Holmes, 1997; Geerts, 2001). The control techniques currently in practise include:
4.1 Chemotherapy and Chemoprophylaxis
Trypanocidals have been employed in treatment and control of AAT for many years. However, new strains resistant strains of trypanosomes have evolved raising issues of concern and further complicating control of AAT in Kenya and other parts of sub-Saharan Africa (Clausen et al., 2010; Mare, 2010). This has been a particular concern for smallholder crop-livestock farmers mainly due to poverty and access to veterinary services. However, the use of a newer chemoprophylactic drugs such as isometamidium chloride, homidium bromide and diminazine aceturate currently used in Kenya and other parts of sub-Saharan Africa has shown excellent results of 12-24 weeks of protection against trypanosomes (Asefa and Abebe, 2001). A study by Munsterman et al., (1992) at Galana ranch in Kenya highlighted chemoprophylaxis where isometamidium chloride given intravenously had not only a good therapeutic outcome but also a considerable prophylactic effect of not less than four weeks in Boran cattle. Mare (2010) reported that prevention of AAT through inoculation of animals with trypanocidals was costly and need a substantial amount of time and thus could not be sustained longer.
4.2 Use of insecticides
Bourne et al., (2005) stated that treating cattle with insecticides to control AAT should always be considered as part of a large-scale tsetse control operation using a range of different and complimentary control techniques. For instance, cattle situated at the edge of a control operation that is adjacent to a tsetse-infested area will be continuously affected by tsetse moving into the controlled area thus to prevent this, it may be necessary to use a protective barrier of targets (Torr et al., 2004). A trial undertaken by the Kenya Trypanosomiasis Research Institute (KETRI) concluded that though the pour-on insecticide (cypermethrin) was very costly, its application led to a significantly reduced tsetse population with further reduction in prevalence of trypanosome infections in animals (Kamau et al., 2000).
4.2.1 Traps and targets
Tsetse flies are easily attracted to coloured cloth traps which can be impregnated with a biodegradable pyrethroid insecticide such as deltamethrin (Kuzoe and Schofield, 2004). These usually use blue or black cloth in a shape that attracts the flies and then funnels them upwards into the netting trap, usually in the form of monoconical or biconical shape (Scientific Working Group, 2001; Maia, 2009).
Well-maintained networks of these traps have proved to be very effective for tsetse control where 4-5% average mortality rates due to use of traps showed 2.6% reduction in tsetse fly per day during the dry spells (Dransfield et al., 1990; Schofield and Kabayo, 2008). However, use of traps had no significant effect on areas with reduced population of tsetse fly though upto 90% decline in fly population was observed (Dransfield et al., 1990). Schofield and Maudlin (2001) showed that such simple technology was convenient and effective. Conversely, in the last few years there has been a breakdown of the public and veterinary health infrastructure in Kenya and the traps have not always been well maintained (Irungu et al., 2006). This has resulted in a massive upsurge in human and animal cases of African trypanosomiasis (Catley and Irungu, 2000). A country-wide programme against African Trypanosomiasis under KETRI has been established that approaches the problem of trypanosomiasis as part of a drive to reduce poverty and promote development in affected areas (Mugunieri et al., 2004; African Network for Drugs and Diagnostics Innovation, 2008).
4.3 Resistant breeds of cattle
Research has shown that there are some indigenous breeds of cattle for example Samba, Laguna, Ankole and Nâ€™dama that have high level of immunity to AAT (Clausen et al., 2010; Mare 2010). Maichomo et al., (2005) showed that Orma Boran and Maasai Zebu crossbreeds of cattle were resistant to AAT which could help minimise the increased mortality and other burdens to the livestock industry in Kenya. Nevertheless, it is evident that such breeds are not kept in many parts of Kenya and more so their level of production is relatively low and more so not productive for use on farm work (Scientific Working Group, 2001; Dietz et al., 2004; Mare, 2010).
4.4 Genetic approaches
Research has been ongoing into developing breeds of cattle that will meet the needs of African farmers i.e. that will have increased level of resistant to AAT, increased production and convenient for use during land preparation (Abenga and Vuza, 2005). As a first step towards this goal, the KETRI and the International Livestock Research Institute (ILRI) in Kenya have ongoing research in separating the genes responsible in making the indigenous breeds of cattle and how they respond to different degree of infection (Wu et al., 2001; Njenga et al., 2007). Though it is still not well known which genes are responsible for the identified resistance, research by Naessens et al., (2002) and Ibeagha-Awemu et al., (2008) identified a common gene between susceptible and resistant cattle breeds of cattle which might bring a major breakthrough in AAT research in the near future.
4.5 Community education intervention
The Kenya Trypanosomiasis Research Institute has been carrying out participatory assessment of bovine trypanosomiasis in villages by working with livestock keepers to analyze different disease and vector control methods (Catley and Irungu, 2000). Involving the community in the control of AAT in Kenya has been yield success in some places. Machila et al., (2006) showed that trypanosomiasis signs knowledge score obtained by the smallholder farmers exposed to the extension materials was higher than that obtained by those not exposed to them. Similarly, farmersâ€™ exposure to extension materials resulted in higher trypanocidal drug knowledge scores among exposed farmers than among those not exposed. These results indicated that over the period monitored, the routes (i.e. school children, village elders, animal health centres and Agrovet shops and media selected) were effective in promoting a significant increase in knowledge of AAT, its causes and ways of dealing with it among livestock keepers (Catley and Irungu, 2000; Machila et al., 2006).
5.0 Socio economic implications
In Kenya, livestock are important in supporting the livelihood of farmers, consumers and traders. However, several studies have shown a high prevalence of trypanosomiasis affecting livestock resulting in reduced animal productivity (Swallow, 1999; Muriuki, 2005). Holmes (1997) and Dinka and Abebe (2005) reported that trypanosomiasis not only had an impact on livestock but also hindered rural development. It has also been shown that trypanosomiasis susceptible livestock herds are always at greater risk of contracting trypanosomiasis in high tsetse fly populated regions (Holmes, 1991; Magez and Radwanska, 2009).
Cases of trypanosomiasis disorient people way of life with and decrease the number of animal a family would have reared (Antoine-Moussiaux et al., 2009). Swallow (1999) reported a 50% reduction in beef and dairy production in AAT endemic areas. In addition, farmers liquid capital is adversely affected by the reduced livestock yields and the imbalanced allocation of resources (Tariku, 2006).
Tsetse transmitted animal trypanosomiasis has drained the Kenyan economy for many years and still there hasnâ€™t been the best solution to the problem. This report has highlighted some of the challenges and current situation about the disease in Kenya.
It is very worrying given that the disease affects both animals and human (Onditi et al., 2007; Ikenna, 2008). Ngâ€™ayo et al., (2005) reported increased challenge in the control of AAT in western parts of Kenya where Trypanosoma rhodesiense was endemic. The control challenges were associated with livestock acquiring natural trypanosome infections important in the transmission life cycle. A number of livestock harbour trypanosomes which also affect man thus, there is need to control AAT in livestock and wildlife in order to have a good general control strategy. However, due to poor surveillance and diagnosis, breakdown of the public and veterinary health infrastructure and high level of poverty among Kenyans, most animal and human cases eventually die of the disease (Swallow, 1999; Thumbi et al., 2010). A recent study by Mihok et al., (2008) reported the dangers of AAT on Kenyan wildlife where 3.6% infection rate due to Glossina pallidipes was reported on black rhino. Moreover, other trypanosomes such as T. congolense and T. vivax infections had tripled affecting bigger population of the wildlife, a situation which if not well looked into may soon wipe out one of the most Kenya treasured wildlife and livestock as a whole.
Even though the use of a newer chemprophylactic drugs has shown excellent results for the prevention of AAT (Mare, 2010), However, they are costly and require ample of time in planning prior to administration thus may not be the best immediate solution (Mare, 2010). In addition, chemotherapy may not work best on savannah areas due to high tsetse density and the increased virulence (Ikenna, 2008).
Genetic approach has been hindered by the high costs and isolation of specific genes which responsible in cattle immunity has not been very evident (Wu et al., 2001; Njenga et al., 2007). While resistant breeds of cattle might be a long term solution, there are some limitations in that such animals are not kept in many parts of Africa and they do not propduce enough to meet the demand for the common citizens. (Dietz et al., 2004; Mare 2010). Use of insecticides has also been highly criticized because of the possibility of killing other non-target flora and fauna (Bourne 2005). However, use of pour-on such as cypermethrin have been of significant in the reduction of tsetse flies population and AAT prevalence in many parts of Kenya (Kamau et al., 2000). Despite the many years of AAT challenges, the Kenyan government has been working towards a long term solution. As a first step towards this goal, KETRI and ILRI in Kenya and other international agencies are currently involved in identifying the genes that African cattle use to respond to infection with trypanosomes with hope to get a long term solution to the problem (Wu et al., 2001; Njenga et al., 2007).
Interestingly, McDermott et al., (2006) showed that the impacts of climate change may have the greatest decrease in the impacts of AAT in semi- arid parts of Kenya by the year 2050 where the climate will be drier hence less vegetation. However, this will have a negative impact on agriculture where the land will be too dry for pastoralism and crop farming.
Tsetse transmitted animal trypanosomiasis hinder socio-economic development in Kenya and other parts of sub-Saharan Africa. In order to control the disease more effectively, the Kenyan government, Bilateral and International Agencies have undertaken new initiatives in training, evaluating the impact of trypanosomiasis on productivity, developing better diagnostic techniques and new drugs, improving techniques of tsetse trapping and control and research into the basis of antigenic variation and trypanotolerance. However, it will still take sometime to arrive to more sustainable control methods especially given the current issues on climate change which may alter tse fly distribution, associated costs and the poor Kenyan economy. Moreover, there is need to carry out detailed epidemiological research and control strategy which will not only target on livestock and humans but also majority of other animal species especially those that live in the wild and may act as a reservoir for the disease.