Import Risk Analysis - Biosecurity New Zealand

13. Plague (Yersinia pestis)
13.1. HAZARD IDENTIFICATION
13.1.1. Aetiological agent
The gram-negative bacterium Yersinia pestis is the causative agent of plague and belongs to
the family Enterobacteriaceae.
13.1.2. OIE List
Not listed.
13.1.3. New Zealand’s status
The last case of Yersinia pestis infection in humans was reported in 1911 during the last
pandemic that started in Hong Kong in 1894. There were 21 cases reported in New Zealand
between 1900 and 1911. Y. pestis is exotic, and listed on the Unwanted Organisms Register
(Ministry of Agriculture & Forestry 2008).
13.1.4. Epidemiology
Plague is a zoonotic disease transmitted and maintained by an obligatory flea-rodent-flea life
cycle involving chronically bacteraemic rodent hosts and their fleas. Humans and domestic
animals are susceptible hosts for Y. pestis (Macey 2006).
Plague exists within particular areas of every continent except Australia. These areas are
generally associated with semiarid, cooler climates that are adjacent to deserts. The
epidemiology in each area is unique, dependent on the rodent reservoir, flea vector, and
environmental factors (Watson et al 2001; Macey 2006).
Many animal species are susceptible and 30-40 rodent species that are relatively resistant to
disease serve as bacteraemic natural reservoirs (Macey 2006; Pauli et al 2006).
Transmission of Y. pestis occurs primarily through flea bites. Following ingestion of
infectious blood, Y. pestis may be cleared by some flea species (Macey 2006). In others,
(particularly rat fleas of the genus Xenopsylla) it replicates in the proventriculus ‘blocking’
the flea so that it starves. During the subsequent increased feeding attempts the bacterium
infects the bite wound of the host (Eisen et al 2007). While many species of flea can be
infected with Y. pestis, fleas of the dog and cat (Ctenocephalides spp.) are considered to be
poor vectors (Macey 2006).
38 • Import risk analysis: Cats, dogs and canine semen MAF Biosecurity New Zealand