; l ' he incidence of Brucellosis in the District of Colombo !

Incidencr of Bn~cellosis in dairy herds in District of Colombo (now Districts of Colombo and Gampaha) has bezn surveyed by use of the Milk Ring Test (MRT) and confirmed by quantitative tests like Standard Agglutination Test (SAT) Complement Fixation Test (CFT) and Coonlbs Test (CT) on suspected sera. In all 305 herds involving 1478 dairy cows were tested giving herd infection of 1.6% and the individual animals infected as 0.9 % The comparatively low infection should not leave room for any complacency. The situation could very well signify the beginning of a widespread infection. Brucellosis has been prevalent in Sri Lanka for several years md therefore it is most appropriate to determine its incidence in localised areas through the veterinary services available in that area. The occurrence of Br~cellosis in the country has been proved by serological evidence as well as isolation of the causal organism from abortting animals.' The reluctance on the part of the owners to permit bleeding their cows for serological tests imposes a limitation of any widespread survey into the incidence of Brucellosis. 011 the other hand, the adoption of the Milk Ring Test (MRT) offers immense potentialities for screening a given population provided the test is reasonably specific and sensitive. The accepted status of the test is that it has found widespread use in localising infected herds, as well as in ensuring that Brucella free herds remain so.' It was therefore decided to screen a representative population of cows in the District of Colombo, which is the area of operation of the Veterinary Investigation Centre, Welisara. This paper records the first detailed study of the incidence of B r u ~ l , losis the District of Colombo (now Districts of Colombo and Gampaha). *Present address : *Veterinary Tnvestigation Centre, Polonnaruwa. $Office of Deputy Dkector (Livestock Farms). Getambe, Peradeniya. 100 U. G. J. S. Wickramasuriya and S. Kumaraswamy 2. Materials and Methods The population tested in the study is mainly the dairy cows which feed the milk collecting centres (MMC) situated in Narahenpita, Meepe, Minuwangoda, Badalgama and Nittambuwa that existed in District of Colombo in 1976. Milk suppliers of the Multi-Purpose Co-operative Society of Attznagalla urere also tested. Also a few farms that did not sv-pply milk to the Nztional Milk Ecard were tested. The animals belonging to milk suppliers of Narahenpita, Meepe, Minuwangoda collecting centres and also those belonging to non-suppliers for Milk Board were tested on the MRT individually, whereas those relating to Badalgama, Nittambuwa centres and suppliers to Multi-Purpose Co-operative Society of Attanagalla were tested on bulk milk samples. 2.1 Scheme of Testing If positive samples are encountered while testing bulk milk samples, all cows corresponding to that milk szmple are tested individually on the MRT method in order to track tl9.e possible reactor/reactors. All individual animals found positive on the MRT are bled and Rose Bengal Plate Test (RBPT) undertaken on the sera at the Veterinary Investigation Centre, Welisara. Immaterial of the results of the RBPT of the serum, duplicate samples of the serum, and the milk preserved in merthiolate ate folwarded to the Veterinary Research Institute, Gannoruwa, Peradeniya for testing on quantitative tests like Standard Agglutination Test (SAT), Complement Fixation Test (CFT) and Coombs Test (CT). All these three tests were done as no single diagnostic test suitable for routine use can be depended upon to detect every infected animal.2 Therefore, cows whose serum Ieact on RBPT and give minimum titres for positivensess, by any one of the above tests, are sonsidered infected with Brucellosis. 2.2. Tests Used 1. Milk Ring Test:The test is based on coloured antigen employed reacting with the antibody present in the milk sampIe and the agglutinating mass thus produced coating itself on the fat globules. The fat globules aggregating antibody normally present in the fresh milk, which rises to the surface of milk column to produce the cream layer. Thus a positive reaction is indicated by a coloured cream ring on the top and white milk column below, whereas a negative reaction is shown by a white cream ring on the top and a coloured milk column below. Extensive studies at the Veterinary Research Institute, Peradeniya, has proved that by finer modification of the original method1,3 the Milk Ring Test.could be adopted even to test individual cows in a herd. Sowing 6f milk in transit partiThe Incidence of Brucellosis in the District of Colombo 101 t cularly in the tropics imposes a severe limitation on the usefulness of the test, but this can be circurnvcnted by preserving the milk sample with merthiolate. It was also been determined that the incubation of the tcst sample for agglutination react~on at room temperature for two hours, g~ves the same results as at 37OC for one hour within an incubator.6 (ii) Rose Bengal Plate Test (RBPT.) The antigen used in the test is prepared at Veterinary Research Institute, Gannomma, Peradcniya., from a culture originally imported from the United States of America. It is buffered at pH 3.65 and has a packed cell volume of 8 % and is stained with Rose Bengal Dyc. The test was performed as described by Alton et a1.l (iii) Standard Agglutination Test (SAT). The antigen used in the test is prepared at the Veterinary Research Institute, Gannoruwa, Peradeniya, from S 99 cu1tu1'e originally imported fiom United Kingdom and is standardised against International Anti-Bnrcella abortus sentm. The test was carricd out as described by AIton et a1.l and a titre of 1/40 by this method represents 80 International Brucclla antibodies per ml of the serum and is considered positive for Brucellosis. (iv) The Coombs Test (CT) The test determines enhancement of titres above the level obtained in the SAT due to incomplete or blocking antibodies, sometimes present being made agglutinable. The ordinary SAT test is used as tbe starting point f o ~ the Coombs Test. The test was done as originally described by Alton et a1.I If there is enlacement of the titre to the level normally considered positive on the SAT, the serum sample is regarded as positive. (v) Complement Fixation Test (CFT). Antigen used in this test is thestandardised CFT antigen obtained from Central Veterinary Laboratory, Weybridge and the technique of the test is based on the'one described by HiL4 All samples giving a titre value of 214 and over are regarded ae positive. 3. Results and Interpretations Table 1 gives the number of herds tested by MRT against each Milk Board Collecting Centre, and the number of heids found positive in each group. Farmers who do not supply milk to Milk Board are also treated as one group in this survey. U. G. J. S. Wickrarnasuriya and S. Kumaraswamy TABLE 1. Number of herds tested by Milk Ring Test Milk Collecting Total No. No. of Farms Total found Centre of suppliers Tested positive