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The epidemiology of Salmonella serovars in Tasmania


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Ball, A 1991 , 'The epidemiology of Salmonella serovars in Tasmania', Coursework Master thesis, University of Tasmania.

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The incidence of human salmonellosis and the distribution of Salmonella
serovars in Tasmania was investigated to provide epidemiological information on
Salmonella occurrence in Tasmania. This baseline data was not available
previously and could contribute information to Australia-wide surveys of
Salmonella and related enteric pathogens and, more specifically, aid in the
prevention of enteric diseases in Tasmania. In addition, the relationship
between Salmonella and indicator organisms in drinking water was investigated.
The incidence of human salmonellosis in Tasmania is 2% in patients with
diarrhoea and 0.13% of the general (asymptomatic) population. This is
comparable to rates on the Australian mainland and in other developed
countries. The disease is most prevalent in summer which is also similar to
seasonal distribution patterns elsewhere. However, the distribution of
salmonellae in Tasmania is unusual in the prevalence of Salmonella mississippi,
a serovar rarely encountered in mainland Australia. This serovar is not
particularly invasive and is unremarkable in the age and sex distribution of its
human hosts or its seasonal variation.
Epidemiological investigation of foods, domestic and wild animals, reticulated
and natural waters, sea water and effluent were undertaken. No particular food
type was implicated as a major source of Salmonella mississippi. Domestic
animals, while having many Salmonella serovars in common with those seen in
the human population, are not a significant source of S.mississippi. Human
infection is likely to be frequently water-borne as 1.6% of 500 reticulated
drinking waters and 8.2% of 250 natural fresh waters contained Salmonella of
which 53% were S.mississippi. The peak incidence of Salmonella in water
occurs in early summer and precedes the summer maximum of human cases.
Salmonella mississippi was isolated from several species of carnivorous and
insectivorous mammals and reptiles but not herbivores. Fifty percent of 120
native cats (Dasyurus viverrinus) sampled were infected with Salmonella and
S.mississippi comprised 97% of these. There was no apparent seasonal
variation of the presence of S.mississippi in native cats. This serovar persisted
in native cats for at least 2-3 months while on a Salmonella-free diet. During
this time no symptoms or ill effects were apparent.
To establish how native cats became infected, components of their diet were
tested. Salmonella mississippi was not isolated from the common pasture pests
which compose the bulk of their diet. However, it was isolated from 62% of 34
metallic skinks (Niveoscincus metallicus) sampled on which they sometimes
prey. This is the commonest of 16 Tasmanian skink species and is endemic to
Tasmania and south east Victoria.
The reservoir of Salmonella mississippi in Tasmania appears to be the native
animal population which contaminates water supplies leading to sporadic human infections.

Item Type: Thesis - Coursework Master
Authors/Creators:Ball, A
Keywords: Salmonella, Salmonellosis
Copyright Holders: The Author
Copyright Information:

Copyright 1991 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Includes bibliographical references (leaves 121-136). Thesis (M.Sc.)--University of Tasmania, 1992

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