Import Risk Analysis - Biosecurity New Zealand

Cats and dogs are classified as spillover hosts where disease occurs in the species only as long as
there is input from an external source. Therefore, the incidence of tuberculosis in dogs and cats is
often a reflection of the local prevalence of tuberculosis in maintenance hosts (Buick 2006).
Specific tests for the diagnosis of tuberculosis in dogs and cats via intra-dermal skin tests and
specific serum antibody responses have been found to be ineffective. Aspirates or biopsy
samples of affected tissues can be stained with Ziehl Neelsen (ZN) stain to confirm
mycobacterial presence. The organism is cultured to determine the species involved.
However, many ZN positive samples fail to grow in culture, and those that do take
approximately 8 weeks (Gunn-Moore 2008). PCR tests are now available, but only for a
limited number of mycobacterial species.
Bovine tuberculosis has been eradicated from many developed countries or is the subject of
eradication campaigns. The eradication campaign in New Zealand is challenging because the
disease is established in brush tailed possums which continually reinfect cattle. Australia is
free from bovine tuberculosis (OIE 2008).
12.1.5. Hazard identification conclusion
M. tuberculosis, M. lepraemurium and M. avium complex are endemic, and not subject to
control or eradication. They are, therefore, concluded not to be potential hazards.
Because M. bovis is subject to a control and eradication programme it is considered to be a
potential hazard.
12.2. RISK ASSESSMENT
12.2.1. Entry assessment
Cats and dogs recently infected or subclinically infected with M. bovis could enter New
Zealand since clinical signs may not be evident.
Therefore the likelihood of entry is non-negligible for cats and dogs imported from countries
that are not bovine tuberculosis free.
12.2.2. Exposure assessment
Transmission of M. bovis from infected cats and dogs to humans or other species has been
postulated but not formally reported. An infected cat or dog would need to excrete an
infective dose via direct contact (aerosol) or by contaminating fomites.
In general, contamination of feed and pasture appears not to be a significant pathway to
transmit the organism, as survival times of infective doses of organisms on fomites are
relatively short under natural conditions. Also, animals are not commonly exposed to a dose
high enough to be infective by the alimentary route. Infection through the oropharyngeal
mucous membrane may be significant, although the infective dose for this route is not known
(Morris et al 1994).
36 • Import risk analysis: Cats, dogs and canine semen MAF Biosecurity New Zealand