Horizontal transmission in sheep and delayed clearance in guinea pigs and mice of a Brucella melitensis Rev. I mutant.

Virulence assays in guinea-pigs, mice and sheep with a Rev. I mutant strain (FSA) demonstrated that the latter had increased virulence in comparison with a reference strain. The mutant showed slower clearance in guinea-pigs and mice when compared with standard Rev. I strains and horizontal transmission was achieved in 2 sheep.

A serological survey of bovine brucellosis in four districts of Bophuthatswana.

Brucellosis testing was carried out in the Moretele and Odi districts of Bophuthatswana. The cattle tested were heifers and cows over 18 months of age (n = 3,374) which grazed on communal tribal lands under extensive ranching conditions. Fifty (1.48%) animals were tested positive with a CFT titre of 30iu ml-1 or higher.

The isolation and serology of the "FSA" Brucella melitensis Rev. 1 mutant in a flock of sheep.

A flock of sheep, known to be infected with the "FSA" mutant of Brucella melitensis Rev. 1, was examined serologically and bacteriologically to determine whether any relationship existed which would help in the control of this infection in the field. An attempt was also made to determine whether vertical transmission occurred. Twenty-one out of 62 sheep were bacteriologically positive. The best organs for isolation were the udder, supramammary lymphnodes and uterus. No significant relationship could be shown between the complement fixation test and bacterial isolation. The absence of any relationship between serological and bacteriological results agrees with a short-lived infection. None of the 24 lambs sacrificed at 5 months showed either serological reactions or were bacteriologically positive, thus no vertical transmission could be shown.

An investigation into alternative methods for the serodiagnosis of dourine.

The complement fixation test (CFT), indirect fluorescent antibody test (IFAT), card agglutination test for trypanosomiasis (CATT) and enzyme-linked immunosorbent assay (ELISA) were compared in their application to the serological diagnosis of Trypanosoma equiperdum infection in 43 horses. The CFT remains a reliable test for dourine, especially in countries where other members of the subgenus Trypanozoon do not occur. The IFAT is a good 'back-up' test, but, requiring skilled operators it has the disadvantage of making it labour intensive, and interpretation of results subjective. This makes it more suited to small numbers of samples. The ELISA is suitable for large numbers of samples and could readily be used in routine diagnostic procedures. The CATT could be of value in field situations, although it does not appear to be as sensitive as the CFT. Its possible application under these conditions should be further investigated.

An ELISA using an SDS extract of Brucella abortus strain 99 as antigen to detect B. abortus antibodies in cattle sera.

An ELISA was developed using an SDS extract of Brucella abortus as antigen to detect antibodies in cattle sera. The antigen was stable at 4 degrees C for at least 4 years and although it gave optimal results at a 1/4,000 dilution it could detect reactors at a 1/32,000 dilution. Based on comparative CF tests on 430 sera from negative herds and 187 sera from positive herds a reading of 0,07 or less using a 492 nm filter could be considered a negative reaction. The ELISA could be a useful test to supplement the CF test but further evaluation is still required.

Brucellosis serology: reduced dose S19 vaccination of yearling heifers versus the use of the standard dose at 5-7 months of age in a clean herd.

In the 427 heifers vaccinated at 12 to 14 months of age with the reduced dose (3 X 10(8) to 1 X 10(9) viable organisms per dose) 3 had antibody titres in the complement fixation test of 196, 688 and 748 IU ml-1, respectively, at 5 months post-inoculation. At 23 to 25 months of age 8/128 (6.3%) of these heifers had rose bengal test (RBT) reactions, at least 6/128 (4.7%) a serum agglutination test (SAT) antibody titre in excess of 30 IU ml-1 and 1/128 had a suspicious reaction in the complement fixation test (CFT) of 30 to 49 IU ml-1. In the 116 heifers inoculated with the standard dose (4 to 12 X 10(10) viable organisms) at 5 to 7 months of age and tested at 22 to 24 months of age, a reactor rate of 37/116 (31.9%) in the RBT was seen. At least 34/116 (29.3%) had antibody titres in excess of 30 IU ml-1 in the SAT. Only 1 animal had a suspicious reaction in the CFT of 18 to 24 IU ml-1. No abortions could be attributed to the vaccine strain and no other isolates of the vaccine strain were made. The possible role of vaccine residues in syringes as a cause of persistent reactions is discussed. The use of disposable syringes is recommended. On serological grounds there appears to be little advantage in using the reduced dose vaccine in yearling heifers as opposed to the standard dose vaccination of 5 to 7 month old heifers.

The relationship between the microtitration serum agglutination and complement fixation tests in bovine brucellosis serology.

The relationship between antibody titres in the microtitration serum agglutination test and the complement fixation test in bovine brucellosis is described. For low and high MSAT values there is good agreement between the 2 tests. This is not the case for MSAT values between 54 and 338 IU/ml. For practical reasons, results falling into this category cannot all be repeated. Repetitions are so structured that less than 4% of the tests need to be repeated. If the level of repetitions should show an increase above 4%, it is assumed that technical or human error has occurred.

Dourine in Southern Africa 1981-1984: serological findings from the Veterinary Research Institute, Onderstepoort.

The distribution of positive dourine cases found on the complement fixation test at the Veterinary Research Institute, Onderstepoort from 1981 to 1984, is recorded. Within the Republic of South Africa, foci of infection occurred in the Johannesburg, Pretoria, Potchefstroom, Rustenburg, Upington, Lichtenburg, Kroonstad, Louis Trichardt, Middelburg (Cape) and Mossel Bay state veterinary districts. In Bophuthatswana, Transkei, Lesotho, South West Africa and Swaziland, positive cases were also recorded. Anti-complementary activity of horse sera does not present a problem. In donkey and mule sera, however, sera show anticomplementary activity in approximately 50% of cases. This can be reduced by diluting the sera 1/2 before inactivating at 63 degrees C for 1 h.

The use of a single complement fixation test technique in bovine brucellosis, Johne's disease, dourine, equine piroplasmosis and Q fever serology.

The same techniques may be used in the complement fixation test (CFT) for the serological diagnosis of bovine brucellosis, Johne's disease (paratuberculosis), dourine, equine piroplasmosis and Q fever (caused by Coxiella burnetii). The reproducibility of results is excellent, falling for the most part within the twofold range and never exceeding the fourfold range. Agreement with other laboratories is excellent (i.e. within twofold) in the case of brucellosis and equine piroplasmosis antibody titres. A good correlation between the occurrence of the disease and serological reactions is found on circumstantial evidence in the cases of dourine, Johne's disease and Q fever. A standard unitage system is used to report the antibody titres found in all the tests. To simplify laboratory protocols, laboratories required to employ the CFT for the diagnosis of these diseases are advised to use a single proven technique in all the tests. Problems experienced with transient false-positive Johne's disease antibody titres in cattle following on tuberculin (bovine and avian) testing make it advisable to take specimens for the Johne's disease test prior to performing the tuberculin tests.