Epidemiology of infection with leptospira species in livestock in Papua New Guinea

The role of infection with Leptospira as a cause of infertility in Papua New Guinea(PNG) has not been confirmed, mainly because of the lack of robust and simple diagnostic tests in PNG. The aims of this study were to determine the seroprevalence and distribution of infection in livestock in PNG and to develop and validate a diagnostic test for use in PNG that was sufficiently accurate and reliable for confident interpretation of the results. The nested and real-time PCRs were assessed for use as diagnostic tools. The first survey was conducted on 3 commercial, 3 smallholder cattle farms and 4 abattoirs in March 2004 in PNG. Each herd was stratified into 3 age groups ( 5 years), and sera from 1379 animals were sampled in Lae and Kimbe. In addition, 73 kidneys were collected from cattle at the abattoir and aseptically processed for culture. Two hundred and eighty three sera were collected from pigs killed at the abattoirs and 79 pig kidneys were collected and cultured. All sera were tested using the microscopic agglutination test (MAT). The dominant serovar infecting the cattle in PNG was Hardjo with a seroprevalence of 53.7%. The prevalence of serovar Hardjo in the six farms and the abattoir was significantly higher than serovars Tarassovi and Pomona (P < 0.05). All pig sera were negative for Leptospira. Leptospires were isolated by culture and the isolates were typed and identified as L. borgpetersenii serovar Hardjo. Cattle are a recognized reservoir for serovar Hardjo and may have a role in transmission to humans. The second survey was conducted in June 2006 to determine if cattle from smallholder farmers, village pigs and dogs in the Markham Valley in Lae, PNG were infected with Leptospira. In addition, pigs from a commercial piggery and horses from commercial and smallholder farms were also sampled. A total of 69 pig sera, 22 dog sera, 15 horse sera and 111 cattle sera were collected. The results showed that 1 dog and 1 pig were seropositive with serovar Canicola. Of the 111 cattle sampled, 21 were seropositive for Hardjo. It was concluded that the seroprevalence with serovar Hardjo in these cattle was significantly lower than cattle from commercial properties. Smallholder cattle may therefore not be a major source of Hardjo infection for animals on commercial farms and pigs do not appear to be infected with Leptospira. The Ab-ELISAs were constructed using one crude preparations of L. interrogans serovar Pomona and 2 different crude preparation of L. biflexa serovar Patoc. The three antigen preparations were evaluated using 21 MAT-positive and 96 MAT-negative pig sera to determine which antigen preparation was suitable for use in an Ab-ELISA. The selected antigen preparation (L1) was validated in the test using serum from 2 cattle and 1 pig population that were seropositive for Leptospira. A sub-population of seronegative cattle and pigs were also used. The Ab-ELISA was used to test 1,465 bovine sera from 8 cattle populations and the results were compared with the MAT using a Bayesian framework, to obtain an unbiased estimate of the accuracy of the tests. The ELISA had high sensitivity and specificity. Results from the Bayesian analysis showed that the sensitivity and specificity estimates for the Ab-ELISA were high compared to the MAT. Based on the test accuracy and its performance the Ab-ELISA using the L1 antigen described in this study is suitable for use in countries like PNG where the MAT is difficult to perform. Samples of kidneys from livestock in PNG were tested using culture and a PCR-based assay to detect Leptospira species. A total of 72 samples of kidney were collected from cattle and a total of 74 samples were collected from pigs slaughtered in Lae and Port Moresby. A second study was designed to assess the use of a real-time PCR for detecting leptospiral DNA in urine from cattle. One hundred and ninety-three urine samples were collected from a beef cattle farm in WA. Whole genomic DNA from kidney samples was extracted from each kidney using the QIAamp DNA Mini kit (Qiagen). Heat lysis was used to extract genomic DNA from clear urine samples and the QIAamp Mini Kit was used for urine that was contaminated with faeces. The PCR-based test was able to detect a higher number of Leptospira-positive kidneys compared to culture in EMJH medium. Results of testing DNA extracted from urine using the realtime PCR showed that this test is sensitive and able to detect cattle infected with pathogenic leptospires.