Cross Species Transmission of Ovine Johne’s Disease – Phase 2 Cattle

Summary

Australian JD control and assurance programs assume that sheep and cattle strains of M paratuberculosis are epidemiologically distinct infections.

This project was undertaken to determine the extent to which Mycobacterium avium subsp. paratuberculosis S strain (OJD) can infect and/or be passively transferred by cattle.

In this study, 1774 cattle on 12 OJD-infected properties (range 90-985 head on each farm) were sampled by serology and faecal culture. All cattle were home-bred on the properties and had thus been exposed to OJD as susceptible calves. Testing was undertaken on the cattle at age 2 years or more. All animals were negative for serology. One property had a single animal with one faecal culture positive (S strain) result, but follow-up serology, faecal culture, post-mortem examination, histopathology and tissue culture were all negative, suggesting passive transfer of the organism (less than 12 months since last infected sheep was on the property) or very early infection.

Management routines that were followed on these properties enabled direct (cattle co-grazing with sheep), and indirect contact to occur (cattle following sheep and sheep following cattle).

An addendum to this report describes additional occurrences of OJD transmission to cattle. During the course of the study, 2 additional properties undergoing Cattle MAP testing each had 2 serological reactor animals which all gave follow-up faecal culture positive results (S strain). Three of these animals were subsequently diagnosed as histologically positive for Johne’s disease. Finalisation of investigation is still pending for the fourth animal. One of these properties did not have sheep present on it, but had infected neighbours adjacent to the calving paddock. The other property was outside the known OJD infected areas, but had raised heifers from weaning to springing on a known OJD infected property. These observations confirm existing beliefs about the risk of transmission of OJD to cattle, i.e. that the risk of transmission is low except where young cattle are reared in contact with infected sheep.

The prevalence of disease in cattle exposed to sheep infected with OJD was assessed as low, but could not be precisely determined. One estimate would be up to 0.4% to 0.6% of cattle running on OJD infected properties may be infected with M paratuberculosis (S strain), based on 1 culture positive out of 1744 animals tested. What is known at present is there are at least 6 cattle herds in NSW infected with OJD.

The likely risk factors associated with cattle developing infection or passive transfer of OJD could not be determined from this study due to the absence of disease. However, in the properties reported in the addendum, exposure to calves may occur due to run-off from infected neighbouring property(s) or from hand feeding sheep and cattle together during drought.