Salmonella alert for home fish tanks

Aquaria may harbour dangerous bacteria responsible for causing gastroenteritis in children and adults, according to NSW Department of Primary Industries (DPI) researchers.

Although rare, in some cases the gastroenteritis was severe enough to cause hospitalisation.

A study led by DPI microbiologists Steven Djordjevic and Renee Levings found that ornamental fish and their tanks are a reservoir for a type of Salmonella bacteria which is resistant to seven antibiotics.

Their research, reported in the March issue of the US journal Emerging Infectious Diseases, found that multi-drug resistant Salmonella paratyphi B (dT+) from patients with symptoms of mild to severe gastroenteritis matched bacteria found in their home aquaria.

Tanks containing both tropical and cold water ornamental fish were a source of this bacterium.

Dr Djordjevic said the findings highlighted the need for careful personal hygiene when handling aquarium fish.

“The fish excrete the bacteria into the water and they can accumulate in the gravel on the bottom.

“The presumed route of infection from fish tanks is from hand to mouth.

“It is vital that people wash their hands, as soon as they have finished touching the tank water, handling fish or cleaning fish tanks.”

The research was undertaken after a Melbourne microbiologist, Dr Diane Lightfoot, reported that multi-drug resistant S. paratyphi B (dT+) from sick patients showed the same antibiotic resistance pattern as isolates recovered from their own fish tanks.

People who became infected had cleaned or handled their home aquaria just before becoming ill.

Dr Djordjevic said that multidrug resistant S. paratyphi B (dT+) has been increasingly isolated from patients with gastroenteritis in Canada, the United Kingdom and France but the sources of these outbreaks has not been determined.

S. paratyphi B (dT+) is resistant to a range of antibiotics including Ampicillin, Chloramphenicol, Florfenicol, Streptomycin, Spectinomycin, Sulfonamides and Tetracycline.

Dr Djordjevic said “antibiotics are often used in the aquaculture industry and aquarium fish are usually swimming in water containing antibiotics during importation.

“Although this bacterium has been found increasingly in the United Kingdom, Canada and France since 1999, the incidence in Australia is difficult to determine as many people do not go to a doctor during mild episodes of gastroenteritis.

”None the less, 76 cases of Salmonella paratyphi B (dT+) were documented between May 2003 and April 2004 - and 18 of these (24%) could be linked to home aquaria.

“Apart from diarrhoea, people with this type of salmonella reported fever, abdominal cramps, vomiting, blood in stools, headaches and muscular pain.

“These observations are important in light of the fact that 12-14% of Australian households own domestic aquariums”, Dr Djordjevic said.

Further information

Elizabeth Macarthur Agricultural Institute