Abstract
BackgroundContagious agalactia (CA) of sheep and goats caused by Mycoplasma agalactiae is a widely occurring economically important disease that is difficult to control. The ELISA is commonly used for the serological detection of CA but it has some limitations and the performance of the available tests have not been properly evaluated.Two commercial ELISA kits are widely used, one involving a fusion protein as target antigen and the other a total antigen. The objectives were to compare these tests by evaluating:i. Their diagnostic sensitivity and specificity, the relevance of the recommended cut-off points, the correlation between the two tests, and, the correlation between serology data and the milk shedding of M. agalatiae;ii. The influence of extrinsic factors such as the targeted animal species, geographical origin of the samples, intra-specific variability of M. agalactiae and concurrent mycoplasma infections.A sample of 5900 animals from 211 farms with continuous CA monitoring for 20 years and no prior vaccination history was used. The infection status was known from prior bacteriological, epidemiological and serological monitoring with a complementary immunoblotting test.ResultsThe average diagnostic sensitivity was 56% [51.8–59.8] for the fusion protein ELISA and 84% [81.3–87.2] for the total antigen ELISA, with noteworthy flock-related variations. The average diagnostic specificity for the fusion protein ELISA was 100% [99.9–100], and for the total antigen ELISA differed significantly between goats and sheep: 99.3% [97.4–99.9] and 95.7% [93.8–97.2] respectively.Experimental inoculations with different M. agalactiae strains revealed that the ELISA kits poorly detected the antibody response to certain strains. Furthermore, test performances varied according to the host species or geographical origin of the samples.Finally, the correlation between milk shedding of M. agalactiae and the presence of detectable antibodies in the blood was poor.ConclusionsThese serological tests are not interchangeable. The choice of a test will depend on the objectives (early detection of infection or disease control program), on the prevalence of infection and the control protocol used. Given the variety of factors that may influence performance, a preliminary assessment of the test in a given situation is recommended prior to widespread use.
Highlights
Contagious agalactia (CA) of sheep and goats caused by Mycoplasma agalactiae is a widely occurring economically important disease that is difficult to control
Agalactiae All 22 sera from infected reference animals had an identical Immunoblotting test (IBT) profile characterized by simultaneous presence of four bands at 80, 48, 40 and 30 kDa and in most cases an additional band at 27 kDa (Figure 1-A)
This profile was identical to the IBT profile obtained with sera from animals experimentally infected with the reference strain PG2 (Figure 2-A-a)
Summary
Contagious agalactia (CA) of sheep and goats caused by Mycoplasma agalactiae is a widely occurring economically important disease that is difficult to control. The objectives were to compare these tests by evaluating: i Their diagnostic sensitivity and specificity, the relevance of the recommended cut-off points, the correlation between the two tests, and, the correlation between serology data and the milk shedding of M. agalatiae; ii. The influence of extrinsic factors such as the targeted animal species, geographical origin of the samples, intra-specific variability of M. agalactiae and concurrent mycoplasma infections. Contagious agalactia (CA) is a disease of sheep and goats mainly characterized by mastitis with a subsequent drop in milk production. The main species in both sheep and goats is Mycoplasma agalactiae and three other species produce a clinically similar disease in goats: M. capricolum subsp. The welfare and especially economic consequences of this disease justify its inclusion in the list of animal diseases of global concern established by the World Organization for Animal Health (OIE) (www.OIE.int)
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