CASE NOTES


A SURVEY OF LEPTOSPIROSIS EXPOSURE IN LIVESTOCK IN THE NORTH WEST, CENTRAL WEST, CENTRAL NORTH, DARLING AND LACHLAN LIVESTOCK HEALTH AND PEST AUTHORITIES OF NSW 

N Charman#, A Hodge#, C Colantoni# and J. Kelly*
# Zoetis Australia Pty Ltd, 5 Rider Boulevard, Rhodes, NSW, 2138
* Central West Local Land Services, 12 Buckley Drive, Coonamble, NSW 2829

This paper was presented at the Combined ACV/ASV Annual Conference, Hobart 2015 and appears in the Proceedings of the Combined Australian Cattle Veterinarians and Australian Sheep Veterinarians (ACV/ASV) Annual Conference, Hobart 2015, pp 180-184.
Posted Flock & Herd June 2015

ABSTRACT

This paper describes a survey conducted to determine the level of Leptospira borgpetersenii serovar Hardjo and Leptospira interrogans serovar Pomona exposure in sheep flocks, cattle herds and feral pig populations in the North West, Central West, Central North, Darling and Lachlan Livestock Health and Pest Authorities in NSW through a serological surveillance of unvaccinated flocks and herds. The survey commenced in December 2011 and ran for a period of 12 months. A total of 146 feral pigs were sampled from 33 different properties during routine culling. 29 cattle properties participated in the survey and 282 samples were collected during routine property visits. The largest contributor to the survey was sheep flocks where 693 samples were collected from 67 different farms. 

In total, 26% of feral pigs sampled, 18% of cattle sampled and 16% of sheep sampled tested MAT positive for Leptospira borgpetersenii serovar Hardjo. 38% of feral pigs sampled, 17% of all cattle sampled and 20% of sheep sampled in this survey tested MAT positive for Leptospira interrogans serovar Pomona. On a per property basis, 61% of the holdings from which feral pigs were culled, 59% of cattle herds and 60% of sheep flocks returned at least one positive result for Leptospira borgpetersenii serovar Hardjo. Similarly, at least one positive MAT result for Leptospira interrogans serovar Pomona was recorded on 61% of the properties from which feral pigs were culled, 62% of cattle herds and 73% of sheep flocks  

Overall, greater than half of all properties contributing to the survey results for each animal species returned at least one positive sample (MAT titre >=80) for Leptospira borgpetersenii serovar Hardjo and Leptospira interrogans serovar Pomona.

MATERIALS AND METHODS 

The program of sero-surveillance enrolled cattle herds and sheep flocks from the North West, Central West, Central North, Darling and Lachlan Livestock Health and Pest Authorities in NSW. At the time of the property visit, approximately 10 plain blood samples were collected from each discrete mob of sheep or cattle. If multiple mobs of sheep or cattle were presented at the time of the visit, additional mobs were sampled up to a maximum of 30 blood samples per property. Feral pigs were blood sampled in conjunction with a culling program conducted in the North West, Central West, Central North and Lachlan Livestock Health and Pest Authorities in NSW. Blood samples were collected on availability of culled animals and accessibility for post mortem blood collection. The individual animal was the experimental unit for this study.

For a Farm/Property to be included in the study, it met the following criteria:

Only samples collected from individual cattle or sheep that met the following criteria were submitted for this study:

Antibody titres to Leptospira interrogans serovar Pomona and Leptospira borgpetersenii serovar Hardjo were determined by utilizing a microscopic agglutination test (MAT). Assays were conducted at both Zoetis VMRD Australia and the NSW DPI – Elizabeth Macarthur Agricultural Institute. A Biometrics Representative from Zoetis VMRD was responsible for all data summaries and analyses.

The key outcome variable for this survey was the overall number and percentage of MAT results for each of Leptospira interrogans serovar Pomona and Leptospira borgpetersenii serovar Hardjo that fell into the following categories:

Negative result – this was assessed as a titre of <=1:50 for each of the two Leptospirosis serovars.

A positive result was assessed as a titre of >=1:80 for each of the two Leptospirosis serovars. These positive results were listed and summarized into three categories.

1. 80 <=MAT titres <320

2. 320 <= MAT titres <640

3. MAT titres >= 640

The secondary outcome variable for this survey was the number and percentage of properties that had at least one positive MAT result for each of Leptospira interrogans serovar Pomona and Leptospira borgpetersenii serovar Hardjo recorded for feral pigs, cattle and sheep.

Farm managers completed and signed the Herd/Flock Enrollment Questionnaire at the time of enrolment and this document constituted their informed consent to participate in this surveillance study. Approval to conduct this study was granted by the CSL/Pfizer Animal Ethics Committee at the meeting held on 29th November 2011 (approval number 897-0).

RESULTS

The individual animal Leptospira borgpetersenii serovar Hardjo results are summarized by species and titre range below in table 1 and displayed graphically in figure 1. 

Table 1: Overall number and percentage of MAT positive results for Leptospira borgpetersenii serovar Hardjo recorded by species
Species L. HARDJO MAT
<=50 80-<320 320-<640 >=640 TOTAL
n % n % n % n % n %
Feral Pigs 108 74.0 33 22.6 4 2.7 1 0.7 146 100.0
Cattle  232 82.3 31 11.0 9 3.2 10 3.5 282 100.0
Sheep 583 84.1 79 11.4 17 2.5 14 2.0 693 100.0
Figure 1: Number of individual MAT positive/negative results for Leptospira borgpetersenii serovar Hardjo recorded overall by livestock species

The individual animal Leptospira interrogans serovar Pomona results are summarized by species and titre range below in table 2 and shown graphically in figure 2. 

Table 2: Overall number and percentage of MAT positive results for Leptospira interrogans serovar Pomona recorded by species
Species L. POMONA MAT
<=50 80-<320 320-<640 >=640 TOTAL
n % n % n % n % n %
Feral Pigs 91 62.3 24 16.4 7 4.8 24 16.4 146 100.0
Cattle  234 83.0 31 11.0 13 4.6 4 1.4 282 100.0
Sheep 557 80.4 93 13.4 27 3.9 16 2.3 693 100.0
Figure 2: Number of individual MAT positive/negative results for Leptospira interrogans serovar Pomona recorded overall by livestock species

The number and percentage of properties that had at least one positive MAT result for Leptospira borgpetersenii serovar Hardjo recorded for each livestock species is shown below in table 3 and represented graphically in figure 3.

Table 3: Number and percentage of properties that had at least one positive MAT result for Leptospira borgpetersenii serovar Hardjo recorded overall by livestock species
Species L. Hardjo Property Status
All Results Negative >=1 Positive Result Total
No Properties % No Properties % No Properties %
Feral Pigs 16 48.5 17 51.5 33 100.0
Cattle  12 41.4 17 58.6 29 100.0
Sheep 27 40.3 40 59.7 67 100.0
Figure 3: Number of properties MAT positive/negative for Leptospira borgpetersenii serovar Hardjo  recorded overall by livestock species

The number and percentage of properties that had at least one positive MAT result for Leptospira interrogans serovar Pomona recorded for each livestock species is shown below in table 4 and depicted graphically in figure 4.

Table 4: Number and percentage of properties that had at least one positive MAT result for Leptospira interrogans serovar Pomona recorded overall by livestock species
Species L. Pomona Property Status
All Results Negative >=1 Positive Result Total
No Properties % No Properties % No Properties %
Feral Pigs 13 39.4 20 60.6 33 100.0
Cattle  11 37.9 18 62.1 29 100.0
Sheep 18 26.9 49 73.1 67 100.0
Figure 4: Number of properties MAT positive/negative for Leptospira interrogans serovar Pomona recorded overall by livestock species

DISCUSSION 

A total of 146 individual samples were collected from feral pigs culled from 33 different properties. 108 (74%) of these feral pig samples tested MAT negative (MAT titre <=50) for Leptospira borgpetersenii serovar Hardjo. The remaining 38 samples tested MAT positive (MAT titre >=80) for Leptospira borgpetersenii serovar Hardjo which is a substantial number considering that the pig is not considered a maintenance host for Leptospira borgpetersenii serovar Hardjo. When the detection of a positive result for Leptospira borgpetersenii serovar Hardjo in feral pigs was considered by property, it became apparent that over half of the properties surveyed (51.5%) returned a positive feral pig result for Leptospira borgpetersenii serovar Hardjo.

The Leptospira interrogans serovar Pomona MAT results for feral pigs followed a similar trend to those for Leptospira borgpetersenii serovar Hardjo, however the rate of seroconversion seemed somewhat higher. 91 (62.3%) of feral pig samples tested MAT negative (MAT titre <=50) for Leptospira interrogans serovar Pomona. Of the 55 samples MAT positive (MAT titre >=80) for Leptospira interrogans serovar Pomona, 24 (16.4% overall) returned a MAT titre >=640 indicating recent or persistent infection with this organism  A total of 20 (60.6%) of the 33 properties from which feral pigs were culled, returned a positive result for Leptospira interrogans serovar Pomona .Given pigs are considered a maintenance host for Leptospira interrogans serovar Pomona, these results are significant for properties recording at least one positive result for Leptospira interrogans serovar Pomona. Feral pigs generally share water sources and grazing/camping areas with both cattle and sheep allowing cross infection to potentially occur through urine contamination of these communal areas.

Cattle and sheep sampled in this serological survey had not previously been vaccinated or had not been vaccinated for at least 24 months with a vaccine containing antigens derived from either Leptospira borgpetersenii serovar Hardjo or Leptospira interrogans serovar Pomona. Serological results obtained through the microscopic agglutination test were therefore a reflection of natural exposure to either Leptospira borgpetersenii serovar Hardjo or Leptospira interrogans serovar Pomona. A total of 282 individual samples were collected from cattle from 29 different properties spread over the three LHPA districts. 232 (82.3%) of all cattle samples tested MAT negative (MAT titre <=50) for Leptospira borgpetersenii serovar Hardjo. The 50 cattle samples that tested MAT positive (MAT titre >=80) for Leptospira borgpetersenii serovar Hardjo were assayed at rates of 11.0%, 3.2% and 3.5% overall in the titre ranges of 80 - <320, 320 - <640 and >=640 respectively. When the detection of a positive assay result for Leptospira borgpetersenii serovar Hardjo in cattle was considered by individual property, 17 of the 29 cattle properties (58.6%) presented at least one positive animal at the time that the sampling took place. 

The Leptospira borgpetersenii serovar Hardjo rates of seroconversion recorded for sheep were broadly similar to cattle. Significantly more sheep were sampled in this survey (693 sheep from 67 properties and 84.1% were classified as negative (MAT titre <=50) for Leptospira borgpetersenii serovar Hardjo. The 110 sheep samples that tested MAT positive (MAT titre >=80) for Leptospira borgpetersenii serovar Hardjo were assayed at rates of 11.4%, 2.5% and 2.0% overall in the titre ranges of 80 - <320, 320 - <640 and >=640 respectively. The detection of at least one positive result for Leptospira borgpetersenii serovar Hardjo by sheep property was calculated at 59.7%, whereby 40 of the 67 properties were classified as positive. This result was consistent with the result for the cattle properties surveyed in this study.

The Leptospira interrogans serovar Pomona MAT results for cattle were of a similar trend to those reported for Leptospira borgpetersenii serovar Hardjo. 234 (83.0%) of all cattle samples tested MAT negative (MAT titre <=50) for Leptospira interrogans serovar Pomona. There were 48 cattle samples (17%) that tested MAT positive (MAT titre >=80) for Leptospira interrogans serovar Pomona. The breakdown of these positive MAT results were 11.0%, 4.6% and 1.4% of the total sample pool in the titre ranges of 80 - <320, 320 - <640 and >=640 respectively. On an overall property basis, the detection of at least one positive result for Leptospira interrogans serovar Pomona in cattle occurred on 18 of the 29 cattle properties (62.1%).

The Leptospira interrogans serovar Pomona rates of seroconversion recorded for sheep again followed the trend seen on cattle farms. 557 of the 693 samples collected (80.4%) were classified as negative (MAT titre <=50) for Leptospira interrogans serovar Pomona (table 17). There were a total of 136 sheep samples that tested MAT positive (MAT titre >=80) for Leptospira interrogans serovar Pomona  and these were assayed at rates of 13.4%, 3.9% and 2.3% overall in the titre ranges of 80 - <320, 320 - <640 and >=640 respectively. The detection of at least one positive result for Leptospira interrogans serovar Pomona by sheep property was calculated at 73.1%, whereby 49 of the 67 properties were classified as positive. This result by property for Leptospira interrogans serovar Pomona was the highest rate recorded for the three species sampled in this survey.

CONCLUSION 

This survey was successful in determining the level of Leptospira borgpetersenii serovar Hardjo and Leptospira interrogans serovar Pomona exposure in sheep flocks, cattle herds and feral pig populations in the North West, Central West, Central North, Darling and Lachlan Livestock Health and Pest Authorities in NSW. Greater than half of all properties contributing to the survey results for each animal species returned at least one positive sample (MAT titre >=80) for Leptospira borgpetersenii serovar Hardjo and Leptospira interrogans serovar Pomona.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the assistance of LHPA staff and farm managers who participated in this survey.

 


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