Interference in diagnostic tests for brucellosis in cattle recently vaccinated against leptospirosis

Abstract

The aim of the current study was to verify if cattle vaccinated against leptospirosis may react in diagnostic tests for brucellosis. Sixty cows were divided into 5 groups, each comprising 12 animals. Four groups were given different vaccines against leptospirosis, while the control group received only saline. Two doses of vaccine were given, as recommended by the manufacturers. Serum samples were collected on the first day of immunization (day 0) and on postvaccination days 7, 14, 21, 28, 35, 42, 49, 56, 96, and 126. All the serum samples were tested for brucellosis and leptospirosis. Twenty animals were reactive at least once to the Rose Bengal test, but by day 96, no further reactions were elicited by this test. Twenty-six samples were reactive to the Rose Bengal test, but only 7 remained positive in confirmatory tests: 1 to the 2-mercaptoethanol test, 2 to the fluorescence polarization assay, and 6 to indirect enzyme-linked immunosorbent assays. None of the samples was reactive in the complement fixation test. None of the animals in the control group was reactive. A significant difference was found between the control group and the groups vaccinated against leptospirosis, according to Fisher exact test. However, the groups were found to respond independently of the vaccine brand. The results indicate that cattle vaccinated against leptospirosis may show reactivity on screening tests for brucellosis.

Antibodies produced by dogs successfully challenged with live Leptospira spp. did not cross-react to Brucella antigen in a commercial rapid slide agglutination test that detects antibodies to Brucella canis

“…Therefore, if RSAT of canine sera collected beyond 14 d post-challenge was performed, testing may have yielded false-positive results. Also, the types of tests used in the previous 7 and current studies differed. An equivalent test used in the previous study to the RSAT used in our study is the rose bengal test.…”

“…2,10,12 Concurrent testing is more common for cattle that have aborted or have other reproductive problems and are suspected to be infected with B. abortus or Leptospira spp. 6,7 However, identifying cattle infected with B. abortus may be 820908V DIXXX10.…”

“…challenging because cross-reactivity of antibodies produced through immunization with Leptospira spp., 7 and other gram-negative bacteria including Yersinia enterocolitica 0:9 and Escherichia coli O157:H7, 4,9 has been documented with some serologic tests for B. abortus and may yield false-positive antibody test results for B. abortus. Similarly, identifying dogs infected with B. canis may be challenging.…”

“…7 Findings between these 2 studies may differ because of the species of Brucella for which an immune response was being detected, the different serovars of Leptospira to which the animals were subjected, the manner in which anti-leptospiral antibodies were induced in vivo, the days of Brucella testing after immunization, and the types of tests used. 7 The cell wall of B. canis has rough or mucoid LPS, and the cell wall of B. abortus has smooth LPS (http://www. nasphv.org/Documents/BrucellaCanisInHumans.pdf).…”

“…such that antibodies directed to them are cross-reactive. 7 The rough LPS of B. canis and B. ovis may be antigenically different from the LPS of Leptospira spp., and therefore, antibodies to the latter did not induce agglutination with this RSAT, which uses B. ovis antigen. The serovars of Leptospira to which these dogs were challenged for our study were 4 of the 6 serovars for which cattle in the previous study were vaccinated.…”