Proceedings Buffalo Workshop December  2001

http://www.mekarn.org/procbuf/pham.htm

Studies on incidence and control of Trypanosomiasis in buffalos caused by Trypanosome avansi steel 1885
 in North Vietnam

 

Pham Si Lang

National Institute of Veterinary Research

Abstract

Trypanosomiasis is a common severe protozoan disease in buffaloes in the Northern provinces of Vietnam. The author and his collaborators have studied the situation of this  parasitic disease and its mechanical vectors from 1985 to 1998, with emphasis on the  control procedures by pharmacoceutical and biological measures.

In examining  the blood samples collected from 8235 buffaloes by routine parasitic methods and inmunodiagnosis  it was estimated  that the infection rate of Trypanosoma  evansi steel 1885 was an average of 7.97%. The highest infection rate was in buffaloes in the Red River Delta provinces attaining 13.4% and the lowest in buffaloes in the Northern mountainous regions (2.0%). These infection rates were influenced by the ecological conditions, the activity of mechanical vectors and the   ages of the hosts.

Samples of biting flies sucking blood of buffaloes from different ecological regions of Vietnam were selected  and identified. There were 10 common species of 3 genus belonging to Tabanidae family and three common specie of three genus belonging to stomoxydinae family (Stomoxys caleinans) They had the capacity to transmit mechanically T. evansi to buffaloes and other  mammals in North Vietnam.

In the hot and wet ecological conditions  of summer in the Red River Delta, T. evansi was transmitted experimentally to four calves by Tabanus rubidus, one of the common species of Tabanus genus in Vietnam. The results confirmed that the experimental calves developed specific symptoms of Trypanosomiasis after 60-78 days of T. evansi infection.

Based by these results, three control measures were established and applied: to control T. evansi infection: by use of a special drug (Naganol Trypamidium); by crossing biting flies of tabonidae and Stomoxydinae by biological measures;  and improving causative agent resistance by good nutrition and reduction of stress. This procedure decreased effectively the T. evansi infection rate from 8.0% to 4.0% in buffaloes herds in the Northern provinces of Vietnam. 

Key words: Buffaloes, Cattle, Trypanosomiasis, T. evansi,  biting flies, control measures

Introduction

Still to now, the Trypanosomiasis caused by Trypanosoma evansi Steel 1885 is the most important haemoprotozoan disease of large ruminants in Viet Nam. Blanchard had detected first T.evansi in blood sample of a diseased mule since 1886 from North - Viet Nam. In following years, the T.evansi infection was found in a lot of domestic mammals as horses, buffaloes and cattle ( Mathis et Leger 1911; Houdemer 1925 Brumpt 1949). Most of the authors commented together that the disease was very severe for horses and mules, but not dangerous for ruminants. In contrast, in recent years, the Vietnamese researchers reported that buffaloes and cattle which, in the northern provinces, caught commonly the surra with heavy clinical signs and died more in Winter and beginning of Spring months when they meet a lot of  environmental stress: insufficient nutrition, hard work and cold weather (Doan Van Phuc 1965; Phan Dich Lan and Pham Sy Lang 1972,1984).

T.evansi was transmitted by gadfly and biting flies species belonging to Tabanidace family and Stomoxydinae subfamily. Among them, some commons species of genera Tabanus were found as: Tabanus rubidus, T.striatus, T.kiangsuensis, T.miser.

 

Methods

Diagnostic methods applied for Trypanosomiasis included wet direct film, Giemsa stain, mice inoculation, parasitictological methods, sero-immunological methods (ELISA, SAT). The composition of the intermediary vector was determined by collecting the disease carrying insects on the bodies of the study cattle, and then classifying these insects using the keys by Sterkhoven, Ricardo and Toumanoff. The biting flies that carried the causative agent were identified using microsurgery method of Powlopsky (1961). T.evansi’s pathogenic activities after entering the biting flies were monitored using Baldry method. The experimental buffaloes and cows were inoculated by insect vectors using the methods of Toumanoff (1939) and Stepanova (1968).

The control procedure was developed and implemented with three main measures:

• Killing and control of T.evansi that infect buffaloes and cows using anti-infection trypanocidal drug including Naganol, Tryamidium Berenil, to be injected to the cattle every April and September.

• Improving weight and disease resistance of buffaloes and cows by good nutrition and proper labor use.

• Reducing the number of disease carrying biting flies by cleaner drainage and ponds around the cages and cattle grazing fields, which are the habitats of the insects, by encouraging the killing of flies to protect buffaloes and cows.

Results

The distribution of Trypanosomiasis in buffaloes and cows in different production/geographical regions:

From 1965 - 1970, the Trypanosomiasis which appeared largely in the buffaloes and cattle population at the Red River delta provinces, killed more working ruminants in the Winter - Spring rice crops.  Nguyen Dang Khai (1996) estimated that some surra outbreaks were detected with 684 sick animals, 186 of which died in three provinces: Hung - Yen, Thai - Binh and Hai - Duong.

In Hoang - long districts (Nam - Dinh province), a low land area, planting two rice crops/year, there were 500 buffaloes and cattle died out of population,     attaining mortality of 6,3%. The cause of this diet of working ruminant was determined by both of Trypanosomiasis and Fascioliasis infections in the Winter - Spring crops.( Phan Dich Lan and  Pham SyLang, 1974).

Survey carried out in buffalo and cattle in 16 provinces consisting of 4 mountainous provinces, 04 intermediate provinces, 04 plain provinces and 04 coastal provinces, estimated that the prevalence of infection was highest in delta area (Table 1). At time, draught buffaloes were transfered from the mountainous and intermediate areas to delta area. These difference in prevalence might be due to stress of travel of buffaloe from mountainous areas to delta areas. Alternatively, the shortage of food in Winter - Spring in delta areas plus working might have produced a high degree of stress in the domestic animals.

 

Table 1 also shows that a higher prevalence in buffaloe than cattle. The light infection rates in buffaloes could be associated with the environmental factors rather than host factors. Buffaloes are used for land preparation in areas of irrigated rice field which probably support higher populations of tabloid flies or differences in feeding preferences of tabanids. Another way, buffalo had been worked hard in the cropping season, while cattle were used to supply meat, reproduction and rarely to plough in the high land. Stress of working and moving from the mountain to delta area could adding to buffalo being more susceptible than cattle.
 

From 1988 to 1995 in areas where T.evansi had caused severe problems in the past, fewer reports of disease were made, the disease appeared regularly in the buffaloe and cattle population in a lot of northern provinces. The various control measure were applied for reduction of Trypanosomiasis infection in domestic ruminants as: treatment yearly with Naganol, trypamidium, improvement of buffaloes and cattle health by good nutrition and changes in agricultural management. 

 

Table 2 shows the results of serological investigation in four provinces in different geographical areas by SAT and CATT. The prevalence of infection varied between 13.1 and 30.1%, Nam ha, in delta area, was the lowest prevalence (Doan Van Phuc 1994; Le Ngoc My 1995, Luong To Thu 1995). Results from surveys at different times and places are not always strictly comparable because of differences in such factors as diagnostic methods and the availability and application of trypanocidal drugs; however, some trends are apparent, the infection rate in delta area becomes the lowest (adverse with result in 1970’s). This situation might be the change of agricultural management leading to improved care of animals, the condition of nutrition, the preventive and treatment of sick animal.  Meanwhile, in the high area, the farmers manage a large herd with traditional farming methods of allowing animals to graze in the forest after the crp season leading to poor husbandry and limited health care.

The serological evidences of infection in Central Vietnam was studied by the slide agglutination test in seven provinces. The prevalence of infection varied between provinces and prevalence rates in buffalo as high as 21.2% and in cattle as low as 6.6% (Le Duc Quyet 1995).

In South Vietnam, from July 1978 to December 1984, investigations of surra in 2,226 buffalo and 1,165 cattle of 9 provinces in the plateau, intermediate, delta areas showed the infection rate 2.7 - 10% by Giemsa stain and MI (Ho Thi Thuan 1984).

From 1988 - 1998, a lot of surra outbreaks have been reported in North - Viet Nam. Table 2 shows the prevalence of  T.evansi in cattle and buffaloes in an epidemic area (Le Ngoc My 1999). Buffaloes were infected more than cattle, except few buffaloes died, the remainder became a carrier. In this area, buffaloes might act as the main reservoir of T.evansi. 

Table 3. Occurence of  T.evansi in cattle and buffaloes in epidemic areas in the intermediate zone.
	Cattle			Buffalo
Village	Number of samples	HEC, MI (+) %	Ag ELISA (+) %	Number of samples	HEC, MI (+) %	Ag ELISA (+) %
H÷u nghÞ	12	0	0	58	9.4	20.7
Quª Nham	20	0	10	41	28.3	24.4
Dai Hoa	31	0	6.5	42	11.1	19.0
Total	63	0	6.3	141	15.0	21.3

 

Table 2 estimates that in outbreaks of surra, the use of Ag-ELISA method to detect T. evansi recorded higher T. evansi infection rates than other methods.

Biological characteristics and pathogenicity of Trypanosoma evansi

 Activities of T.evansi in the body of insect vector

The research results have shown that in the hot and humid climatic condition of northern Vietnam: temperature of 25-34⁰ C; humidity of 80-100%, Trypanosoma evansi, after entering the digestive tract of Tabanus rubidus, could survive up to 53 hours but the pathogenic activity was only maintained until the 7th hour.

In 1972, an experimental Trypanosomiasis transmission was successfully carried out to transmit T.evansi to cows from Tabanus rubidus. 4 calves of 2-year-old were observed to be infected after being bitten by the insect vector for 43 minutes. There was a 80-minute interval between the time when a fly bit a healthy calf and when it bit an infected calf. The calf incubated the disease for 24 days, with high fever (41⁰C) and edema under the skin.

 

Species composition of the insect vector

According to investigation reports by Trinh Van Thinh (1968), Phan Dich Lan (1974), there are 42 gadfly species belonging to the three genera Tabanus, Chrysops and chrysozona, family Tabanidae and 4 biting fly species belonging to the three genera Stomoxys, Liperosia and Bdellollarynx of the family branch Stomxydinae. Since 1962-1979, in many different geographical regions, we once again confirmed the presence of a majority of the fly species mentioned above, in which 7 gadfly species and 3 biting fly species with broad distribution range have been identified as major T.evansi carriers to buffaloes, cows and other mammals:

Gadfly species:

1) Tabanus rubidus Wiedemann

2) T.striatus Fabricius

3) T.kiangsuensis Kiober 

4) T.miser Szil 

5) T.brunneothorax Stekhoven 

6) Chrysops dispar Fabriciu

7) Chrysozona assamensis Ricardo

Biting fly species: 

8) Stomoxys calcitrans (Linneaus) 
9) Liperosia exigua de Meijère 
10) Bdellolarynx sanguinolentus Austen
 

Topographical features had an impact on the distribution of the gadfly species. Those that belong to genera Chrysops and Chrysozona inhabit mainly in mountainous and intermediate regions. Species of genus Tabanus are found everywhere: 26 species in mountainous areas, 14 species in intermediate areas, 8 species in the plains and coastal areas. In mountainous areas, there are a great number of species, but few individuals. On the contrary, in plain areas, the species composition is not rich, but the number of individuals is significant.

As a result, the pathogenic activity of gadflies and biting flies is very common and powerful. This explains why there was a higher percentage of infection in buffaloes and cows in the plains than in mountainous areas.

Characteristic clinical signs of infected buffaloes and cows

Clinical signs:

251 buffaloes that had been naturally infected were studied and there were 68 acute cases (25.5%), 179 chronic cases (71.3%) and 9 non-manifest cases (3.1%). The characteristic clinical signs were:

1) Interrupted high fever: 40⁰C: Seen at 208 buffaloes, accounting for   88.1%.

2) Weak and thin body, anemia: Seen at 211 buffaloes (93.6%).

3) Yellows of mucous membrane: Seen at 69 buffaloes (29.0%).

4) Edema of lower body part: Seen at 73 buffaloes (30.8%).

5) Inflammation and edema of shoulder and thigh nodes: Seen at 37 buffaloes (15.7%).

6) Severe diarrhea, feces containing mucous membrane: Seen at 26 buffaloes (11.0%). 

7) Discontinuous and non-ending diarrhea: Seen at 84 buffaloes (35.5%).

8) Inflammation of eye conjunctiva and cornea: Seen at 12 buffaloes (78.4%).

9) Nervous syndrome: shaking seizure by seizure: Seen at 107 buffaloes (45.1%).

10) Serious hysterical: Seen at 29 buffaloes (12.3%).

11) Paralysis of rear legs: Seen at 36 buffaloes (15.2%).

12) Non-manifest, carrying the parasites: Seen at 9 buffaloes (3.2%).

Lesions

On examining the sick and dying buffaloes, some typical lesions have been identified: the flesh is flabby, faded in colour, edema (73.8%), having a yellow glutinous substance subcutaneouly (56.5%), big and flabby spleen (73.8%), the heart is flabby with yellow solution in heart membrane and conjection occurs in patches in the ventricle (69.5%), having yellow solution in abdominal cavity (62.2%).

In cows, there were similar clinical symptoms to those in buffaloes, but at a slighter severity.

 

The results of the development and implementation of the disease prevention plan.

The T.evansi causative agent can only be transmitted to a healthy cattle animal by an intermediate vector, either a gadfly or a biting fly that bite an infected animal. These intermediate insects are widely distributed and active all year round, therefore it is possible for them to transmit the concerned disease all year round, especially in hot months. Thus the prevention plan must include three major measures:

Clearing of the causative agent on the host body:

Buffaloes and cows at cattle grazing farms had to have regular blood tests so that potential sick animals can be identified and treated early, hence eliminating the natural potential reserve of the causative agent.

Keeping the causative agent from entering the buffaloes and cows:

Where an epidemic occurs, buffaloes and cows should be used Trypanocidal drug twice a year in April and September. The vaccine is either:

Naganol: used at dose of 0.02g/kg weight of the animal, injected twice 2-3 days apart.

Trypamidum: used at dose of 0.001g/kg weight, injected once on muscle or veins.

Berenil: used at dose 0.0035g/kg weight of animal, infected twice 7-8 days apart

 

According to Touratier (1979), Naganol and Trypamidium have the ability of keeping the injected animals free of the disease for 2-3 months and 3-4 months, respectively, after injection. In areas that have fewer than 5% T.evansi infection, only the reportedly infected buffaloes and cows will be treated.

In cattle breeding and grazing farms, trypanocid is held twice a year in hot months when the insect vector is the most active. Whenever there is a translocation of cattle herd from the mountainous areas or epidemic areas to plain areas, it is vital that test and trypanocid are conducted before the translocation. Improving weight and disease- resistance through good nutrition and proper labour use.

Measures to reduce number of disease-carrying insects

• Killing gadflies and biting flies manually.

• Cattle cages and farms should have curtains to prevent the flies.

• Good housekeeping and sanitary measures are encouraged such as the better drainage around the grazing farms and fields, practicing compost that would leave the flies no place of living and reproduction.

The above disease prevention plan measures have been developed and implemented at a range of districts such as Binh Luc, Kim Thanh, Hoang Long (Ha Nam province), Thanh Tri, Tu Liem, Dong Anh (Hanoi), Thanh Oai, Yen Thuy, Lac Son (Ha Tay). The results have shown that districts that have complied with the prevention plan including regular use of Trypanocidal drug of the cattle stock have basically reduced the frequency and intensity of Trypanosomiasis in winter-spring crops. For example, in Binh Luc, in 1979-1980 there were 542 out of total 4.582 buffaloes and cows (13.5%) fell down because of the disease with T.evansi infection percentage of 14.2%. After 2 years of implementing the prevention measures, the number of infected cattle fell to 6.3%, and the infection percentage also decreased to 4.3%% in the winter-spring crop 1981-1982. Other districts have achieved similar outcomes after the implementation of the prevention plan.

 

Conclusion

From the research results discussed above, we have come up with some conclusions as follows:

• Trypanosomiasis in buffaloes and cattle are a very common disease in northern provinces caused by Trypanosoma evansi Steel 1885. Which is one of important causatives agents to kill more working domestic ruminants. In all geographic areas whether they are mountainous, intermediate, plain or coastal, buffaloes and cows were all infected with Trypanosomiasis. However the infection rates depended upon local ecological conditions and the activity of the insect vector.
• Under stress in winter-spring crops (coldness, food short-supply, heavy work), the buffaloes that have been T.evansi infected lost their biological balance, their resistance reduced and they died very quickly, particularly in the case of the cattle herd being translocated from mountainous areas to the plain provinces.
• Under the hot and humid climatic conditions of northern Vietnam, the species composition of the insect vector is very abundant, including 42 gadfly species belonging to family Tabanidae and 3 biting fly species belonging to the subfamily Stomoxydinae. Among these, there are 7 gadfly species and 3 biting fly species that are popularly mainly responsible for the transmission of T.evansi to buffaloes, cows and other mammals.
• It has been experimentally acknowledged that T.evansi could survive 53 hours and were capable of infecting animals until 7th hour after they entered Tabanus rubidus. We were able to transfer successfully T. evansi to calves using Tabanus rubidus. It took 80 minutes from the time when Tabanus rubidous bit an infected calve to the time they bit a healthy calve.
• By studying 251 infected buffaloes, it has been recorded that 25.5% of the incidents were acute, 71.3% were chronic and non-manifest 3.2%. Characteristic clinical signs are comprised of: interrupted high fever, nervous syndromes, edema, paralysis of rear legs, anaemia, lactation and death due to exhaustion.
• The Trypanosomiasis control procedure put in place has included three major measures: Using trypanocidal drug to treat sick animals (Naganol, Trypanidium, Berenil); good nutrition and management of the cattle stock; killing insect vector mechanically and biologically. The control procedure has been effectively applied in many districts, help minimize the losses caused by the disease and protect the buffaloes and cow stock in northern provinces of Vietnam.

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