Trop. Anita. Hlth Prod. (1992) 24, 9-14

PREVALENCE OF BABESIA BOVIS AND ANAPLASMA MARGINALE AT SELECTED LOCALITIES IN SRI LANKA W. K. JORGENSEN, D. J. WEILGAMA, M. NAVARATNE' and R. J. DALGLIESH~ Tick Ferer Research Centre, Queensland Department of Primary Industries, 280 Grindle Road, Wacol, Brisbane 4076, Australia; i Veterinary, Research Institute, Peradeniva, Sri Lanka SUMMARY

Sera were collectedfrom a minimum ~?['20cattle aged nine to 36 months at each of 14 localities in five climatic zones of Sri Lanka. Sera were tested for antibodies to Babesia bovis and Anaplasma by an indirect fluorescent antibody test and a card agghabmtion test, respectively. Antibodies to B. bovis and Anaplasma were detected in all samples tested JFom each of 14 and 12 localities respectively. In general, prevalences were consistently high among localities below 1,200 m and lower and more variable in the hill country. Management practice rather than climate was considered to be the main factor influencing prevalences. Mangement is discussed in relation to the risk of disease outbreak.

INTRODUCTION

The tick-borne haemoparasites Babesia boris, B. bigemina and Anaplasma marginale are endemic in Sri Lanka (Nugera and Fernando, 1963; Abeysena and Seneviratna, 1970). Vaccination procedures to protect susceptible imported cattle and their progeny were first implemented during the late 1940s (Nugera and Fernando, 1963) and recently revised (Weilgama et al., 1989). However, little is known about the prevalence of the parasites in different parts of the country. Therefore, the risk of disease and how best to use vaccines have been difficult to assess. This paper summarises data obtained in a study undertaken to determine the distribution and prevalence of B. bovis and A. marginale infections in cattle located in different climatic zones of Sri Lanka. The findings are discussed in relation to the effects of climate and different management practices on the risk of disease outbreaks. MATERIALS AND METHODS

Sample collection Sampling localities were mainly co-operating farms in Sri Lanka where cattle were present in sufficient numbers to provide a sample size of 20 or more from each location. The localities represented five of the six climatic zones (Tables I and II). During the period from January 1986 to October 1988, 13 cattle farms and one veterinary range (Table II and Fig. 1) were visited. Cattle farms were either government or privately owned and each held more than 200 head. The veterinary range (Dambulla) was an area covered by a local veterinarian for small holders who had up to three cows with calves. Other veterinary ranges were not sampled as many of the cattle in these were introduced from other areas and already vaccinated against B. bovis with a live vaccine. No farms were visited in the regions north and north-east of Poionnaruwa due to civil unrest. At each farm, 20 to 70 cattle were identified from farm records as being between nine and 36 months of age, born on the property and not previously immunised against babesiosis or anaplasmosis. Within the Dambulla veterinary range, insufficient animals were available in the nine to 36 month age range and samples from older animals were

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JORGENSEN. WEILGAMA. NAVARATNE AND DALGLIESH

TABLE I Parameters for different climatic zones in Sri Lanka Zone name

Height above sea level (m)

Hill country Wet zone

> 1,200

Mid country

450-1,200

2,500-6,250

Dry zone Wet zone

Low country

Rainfall per annum (ram)

1,250--1,500 1,500-5,000 < 450

Dry zone Intermediate zone Wet zone

< 1,250 1,250-2,500 1,875-2,500

included. Animals under nine months of age were excluded from the study to avoid serological detection of the dam's colostral antibodies to Babesia or Anaplasma. During each..visit, each animal in a sample group was bled for serum. General information on husbandry practices and the prevalence of ticks was obtained with a subjective assessment of tick burdens made on the cattle sampled.

Sample testing Serum was tested at the Veterinary Research Institute, Kandy. The samples were stored in sterile 5 ml vials at - 2 0 ~ until tested for antibodies to B. bovis by an indirect fluorescent antibody test (IFAT) (Callow et al., 1987) and to Anaplasma by a card agglutination test (Amerault and Roby, 1968). For each test, weak positive and negative sera were used as controls. These positive and negative sera had been collected in Australia from chronically infected cattle and haemoparasite-free cattle respectively and stored in liquid nitrogen until used. RESULTS

The results obtained from the 14 sites sampled are shown in Table II. Antibodies to B. boris and Anaplasma were detected in cattle from all localities tested. The percentages of cattle with antibodies were more variable in localities in the hill country zone. DISCUSSION

The main purpose in sampling selected groups of cattle in widely separated localities was to determine the approximate distribution of B. boris and A. marginale in Sri Lanka. The results showed that the two parasite species were present in all of the localities tested, and suggested that climatic difference had no substantial effect on distribution of the parasites. A second objective was to assess the risk o f disease outbreaks occurring in the particular localities selected. This assessment, at least for B. bovis, can be based on the seroprevalence of antibodies in groups of cattle over nine months of age (Mahoney and Ross, 1972). At this age coiostral immunity and calfhood resistance have waned and cattle without antibodies are potentially at risk from disease. Our survey was restricted to a single sampling on all but one property, so that changes in risk with time could not be assessed. Nevertheless, the available data and knowledge of prevailing management practices allow certain conclusions to be drawn.

BABESIA AND ANAPLASMA IN SRI LANKA

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TABLE II Percentages of nine to 36 month old cattle seropositive to Babesia boris and A n a p l a s m a at selected localities in Sri Lanka

Climatic zone ~ Hill country Wet zone Wet zone Wet zone Wet zone Wet zone

Locality-' (Map location)

Breed 3

Ambewela Farm (I) New Zealand Farm (2) Seven Hills Private Farm (3) Bowpatalawa Farm (4) Dayagama Farm (5)

BT

Mid country Wet zone

Haragama Farm (6)

Low country Dry zone Dry zone

Polonnaruwa Farm (7) Wirawila Farm (8) Ridiyagama Farm (9) Dambulla Veterinary range (10) Nikaweratiya Farm (I 1) Melsiripura Farm (12) Karagoda-Uyangoda Farm (I 3) Bingiryia Farm (14)

Dry zone Dry zone Intermediate zone Intermediate zone Intermediate zone Wet zone

Sample size

% B. boris 4

% A. marginale 5

84 13 88

18 0 98

BT

62A 6 30B 40

BT

20

5

80

BT

19

53

74

BT

60

I00

90

BTX BTX

26

85

88

BI BI B1X

27

100

44

74

91

30

BI

34

62

56

BI BI BIX

69

96

ND 7

21

90

90

BTX BIX BT Bi BIX

27

I00

48

34

94

38

33

100

ND

Climatic Zones--see Table I. -"Locality--number in brackets indicates position on Fig. 1. Breed: BT = Bos taurus BI = Bos indicus. BTX = predominantly Bos taurus cross BIX = predominantly Bos indicus cross. 4 Percentage of serum samples positive in IFA test for B. boris antibodies. 5 Percentage of serum samples positive in card agglutination test for Anaplasma antibodies. 6Samples A and B were taken 12 m o n t h s apart. 7ND = not done.

The comparatively low proportion of cattle with antibodies to B. bovis in certain groups in the Hill Country zone was indicative of high risk of serious disease outbreaks. This risk is compounded by the fact that these groups comprise Bos taurus breeds genetically most susceptible to B. boris infection. The low seroprevalence on these farms probably results from the management practice, common to many hill country farms, of maintaining calves indoors and away from tick-infested pastures until nine months of age. This conclusion is supported by data obtained from the two sets of samples taken from Ambewela farm 12 months apart (Table II, samples A and B). Sample A is from animals that were nine to 20 months of age and had been sent out to graze. Sample B were from nine to 1i month old calves that had not been allowed

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JORGENSEN. WEILGAMA, NAVARATNE AND DALGLIESH

Prevalence of Babesia bovis and Anaplasma marginale at selected localities in Sri Lanka.

Sera were collected from a minimum of 20 cattle aged nine to 36 months at each of 14 localities in five climatic zones of Sri Lanka. Sera were tested ...
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