The prevalence of Salmonella and the spatial distribution of its serovars amongst New Zealand's native lizards : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
This thesis considers the prevalence and spatial distribution of Salmonella serovars
amongst wild endemic lizards on offshore islands around the coast of New Zealand.
The mean test prevalence of faecal excretion of Salmonella was 4.7%. Skinks
(Scincidae) were more likely (8.5%) to be carriers of Salmonella than geckos (1.6%).
Each island was host to between one and three Salmonella serovars that were not found
on any other islands in this study. Two exceptions were Salmonella Bousso and
Salmonella Mana which were found on two islands within the same geographical area.
Based on the findings of this study, different islands are likely to be hosts to different
Salmonella serovars which could have implications for future translocations of native
I also assessed the prevalence and spatial distribution of faecal excretion of Salmonella,
Aeromonas and Hafnia alvei within Mana Island. The prevalence of Salmonella on
Mana Island was estimated at 5.8%. Salmonella was found predominantly in skinks
(10.0%) and less often in geckos (4.1%). H. alvei was found at a prevalence of 1.9%.
No Aeromonas species were cultured from any of the cloacal swabs, suggesting that the
95% confidence interval for the true prevalence is 0-3%. Each site sampled in this
study was host to one or more unique serovar of Salmonella not found at any of the
other sites. The results of this study indicate that Salmonella serovars may become
established within populations of lizards and is not spread between them. This may be
due to a lack of dispersal of lizards between sites, raising important considerations for
the translocation of native lizards.
I investigated the prevalence of faecal excretion of Salmonella, H. alvei and Aeromonas
by New Zealand native lizards from two captive populations. The mean prevalence of
faecal excretion of Salmonella in the captive lizards sampled was 11.5%. There was a
higher prevalence of Salmonella within captive population A (22.0%) than in population
B (3.6%). No Aeromonas was cultured from any of the lizards. H. alvei was found at a
prevalence of 5.2%. The prevalence of Salmonella and H. alvei was significantly higher
in captive lizards than in wild populations. Captive lizards may, therefore, not be
appropriate founders for new populations of wild lizards.
Finally I assessed the different efficiencies of two media and two temperatures in
isolating six Salmonella serovars from a reptilian source. All serovars grew equally
well at 37°C and 27°C. For most serovars XLD agar was the more successful media
than MacConkey agar but the success of different culture media depended on the
serovar being cultured. Because lizards are frequently host to a wide range of
Salmonella serovars, screening samples using multiple microbiological methods is
likely to give the best chance of isolating all Salmonella serovars present.