Comparison Of Assays For The Diagnosis Of Mycobacterium Avium Subsp.paratuberculosis In Dairy Cattle

Paratuberculosis is a chronic infection, which has been of particular concern in ruminants. The infection is caused by Mycobacterium avium subsp. paratuberculosis (MAP). The major effects of the infection on the animal level can be reduced milk yield, premature culling and reduced slaughter value, and losses due to continued spread of the infection. Control of the infection can be obtained via timely detection and culling of infectious animals and reduction of transmission from these animals. One study was performed on two dairy cattle herds with a history of clinical paratuberculosis, to evaluate different enzyme-linked imMolunosorbent assays (ELISAs).According to the result of evaluation, the test kit from IDEXX was chosen to finish an epidemiological survey of MAP of dairy farms in Beijing. Another study was performed to analyse the association among results of a serum enzyme-linked imMolunosorbent assay (ELISA) and two different PCR tests on faeces for Mycobacterium avium subsp. paratuberculosis detetion in dairy cows.1. Serum samples and faecal samples obtained from333animals were analysed using two ELISAs to detect antibodies to Mycobacterium avium subsp. paratuberculosis (MAP). Kappa (κ) concordance coeffecients in pairwise comparisons of the ELISA outcomes ranged up to0.19. The results indicate that neither the two serum ELISAs are effective for the early individual detection of MAP in dairy cattle. They are still the method of choice for epidemiological studies and herd-based diagnosi.2. An epidemiological survey of MAP of2dairy farms in Beijing was made with comMolercial ELISA-Ab test kit. The result showed that both of the herds have antibody postactive animals.The positive rates of herd A and B were8.5%and32.4%relevantly. The total positive rate of cows was22.1%. This study indicates that the prevalence of paratuberculosis in dairy farms is serious in Beijing.3. Faeces and blood samples were collected from365lactating dairy cows in two known infected herds and were analysed using an ELISA to detect antibodies to Mycobacterium avium subsp. paratuberculosis (MAP) and two PCR methods (PCR1is based on IS900sequence,its pramers are MP3(CTG GCT ACC AAA CTC CCG A,5’-3’)and MP4(GAA CTC AGC GCC CAG GAT,5’-3’); PCR2is based on f57sequence, its pramers are F57(CCT GTC TAA TTC GAT CAC GGACTA GA,5’-3’) and R57(TCA GCT ATT GGT GTA CCG AAT GT,5’-3’) to detect the agent. Results were analysed to determine associations and levels of agreement between pairs of tests. A total of122animals (33.4%) tested positive when all the tests were interpreted in parallel. ELISA and PCR2resulted in the highest kappa coefficient (0.122; slight agreement), followed by PCR1and PCR2(0.03; slight agreement), with the lowest agreement being for ELISA and PCR1(-0.085; poor agreement). Enzyme-linked imMoluosor-bent assays showed the highest complementary sensitivity values for all the possible two-test combinations, followed by faecal PCR1. The combined use of ELISA and faecal PCR has the potential to increase the overall sensitivity for the diagnosis of paratuberculosis infection.