Haemoprotozoan diseases rank high in importance amongst parasites of livestock and even man. Diseases caused by them have devastating effect on livestock wealth leading to heavy economic losses. These loses are due to reduced productivity, mortality and cost of treatment. These diseases are present throughout the world, but are most numerous and exert their greatest impact in the tropical and subtropical regions because of greatest vector activity in these regions. In India, they are the major health impediments to efficient livestock production. The economic toll caused by these diseases is staggering. Better global control of tick-borne diseases of livestock and their vectors would contribute substantially to improved meat and milk production. The important haemoprotozoan diseases that are affecting the livestock are as under.
Trypanosomiasis is the most widely distributed disease of animals, affecting domesticated livestock in Asia, Africa and Central and South America. Its spread into South East Asia has occurred only relatively recently, and the serious epidemics of trypanosomiasis were recorded in the early years of the present century in Indonesia and the Philippines, suggest that it could have spread into these regions within the last 100 years. Trypanosomiasiss is also known as ‘Surra’ (rotten) in India. T.evansi identified by Sir Griffth Evans in 1880 was the first trypanosome shown to be pathogenic for mammals (Gill, 1991).
In India disease is mainly common in northern part of the country. The incidence of the disease varies with the activity of vector and the disease has seasonal and endemic distribution. The disease is encountered after the onset of monsoon due to presence of large population of biting flies from July to November with the peak from august to October (Prasad et.al.1991).However, few cases may occur from January to June. The worst affected areas are Punjab, Uttar Pradesh, Uttaranchal, Gujrat, Rajasthan and incidence are also reported from Bengal, Assam, Maharashtra and Madhya Pradesh. The occurrence of disease has also been reported from R.S.Pura and adjoining Samba tehsil of Jammu Division, Jammu and Kashmir (Raina et.al, 2000).
Trypanosomiasis is primarily a disease of domesticated livestock, and infections in wild animals are acquired secondarily and the disease is often fatal. Many species of domesticated livestock can be infected with T. evansi, although the principle host varies geographically. In Africa camels (Dia et al. 1997), in Central and South America horse are the most important hosts. In Asia, hosts include Bactrian and dromedary camels, cattle, buffalo, horses and pigs . There are reports of infection in goats and sheep (Boid et al. 1981).
Distribution: (Radostits, et. al., 2000)
( Tsetse fly )
|Africa, Asia South and Central America
|Africa, Asia, Europe, and America
|East, Central and South Africa
|Gambian Sleeping Sickness
|West and Central Africa
|South and Central America, Southern U.S.
|Rhodnius Spp. Triotoma Spp. (Kissing bug)
Both cattle and buffalo can act as symptom less carriers of infection and horses with fulminating infections are a dangerous source of infection for cattle or buffalo (Luckins, 1996).It is not clear to what extent wild-animal foci of infection exist. Tiger, fox, jackal, hyena, mongoose, Capybara, wild dogs and deer have also been shown to be infected with T. evansi.
Disease is transmitted by biting flies like species of Tabanus, stomoxys, haematopota ,Chrysops, Lyperosia and Hippobasca. Ticks like Ornithodoros crossi and O.lahorensis are also involved in the transmission of T.evansi. Ingestion of meat from infected carcasses by carnivores can also result in infections. In South America, vampire bats are both reservoirs of infection and vectors. The most important vectors in open conditions of the field are Tabanus spp, Transmission succeeds if feeding take place within one hour of the infective feed, thereafter the likelihood declines marked.
Surra is invariably sever and often fatal in camels and horses whereas milder disease in cattle, but camels may exhibit chronic signs lasting for 3 years given name”Tibersa”. The clinical characteristics of infection is similar amongst the different species of host animals and includes a progressive anemia, high temperature, marked depression, dullness, loss of condition, circling movements and in some cases, death. Reproductive wastage has been identified occasionally. Abortion, weight loss and reduced draught power are major causes of economical losses. In the field, reports of disease in camels, buffalo, cattle, horses and pigs are well documented.
Diagnosis of the disease is based on: (a) history of prevalence of vectors, (b) clinical symptoms and (c) laboratory examination of blood and body fluids by direct examination, chemical tests, animal inoculation test and immunodiagnostic tests.
Demonstration of trypanosomes in fresh / stained blood smears from infected animal is the surest way of establishing the acute infection since the organisms are readily demonstrable in freshly stained blood smears.
The tests are non-specific and far less reliable but may find place in the field for immediate tentative diagnosis.
iii) Thymol turbidity test: The test is indicated for cryptic cases of surra in camel and is proved to be superior to mercuric chloride test. Alkaline thymol buffer (3ml) is mixed with 1 drop of suspected serum (inactivated at 560C for 30 min). Immediate white turbidity, increasing maximum up to 1 hr. appears in positive cases.
Treatment and Control
Treatment with trypanocidal drugs is the usual method of control of T. evansi, and five compounds, suramin, diminazene, isometamidium, quinapyramine and cymelarsen have been used.
Suramin has been the mainstay of treatment for all host species for over 70 years. Quinapyramine has been used in camels and horses whilst Diminazene and Isometamidium have been used for treatment of cattle and buffalo. Cymelarsen has been introduced only recently for treatment of surra in camels. Diminazene has been used successfully to treat cattle and buffalo in India and Thailand, but there are some doubts about its efficacy at the recommended dose rate of 3.5 mg/kg; some suggest a higher dose. Control of Trypanosomiasis is limited to treating animals that are considered infected on the basis of the clinical signs, or treatment of animals showing patent infection. Treatment of proven infected, or clinically affected animals, fails to address the underlying problem of carrier animals. The low sensitivity of parasitological techniques and the unreliability of clinical signs ensures that this approach cannot decrease the number of cases as effectively as treating all infected individuals. If wildlife reservoirs are of no importance, and if small ruminants and dogs present little or no problem, then it should be possible to effect control based solely on the use of chemotherapy.
Preventive measures used by livestock owners to discourage attacks by biting flies include stabling animals, use of smudge fires, installation of netting to protect dairy cattle, Prophylactic treatment and good husbandry of animals at risk, and development of trypanotolerant animals like N’dama, Maturu of Africa. There is no vaccine available against the disease and in spite of intensive research, none appears likely in the near future because of the ability of trypanosomes to readily change their glycoprotein surface through a process called antigenic variation (Radostits et.al.,2000)
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