Kangaroo Island Cat Control Committee

With the decline of Tasmania's devil population from DFT there is strong evidence the state's feral cat numbers are increasing.

Apart from the implications for wildlife the increase also poses a threat to human health through the spread of toxoplasmosis, a disease veterinary pathologist David Obendorf believes should be recognised as notifiable. "As well as being an environmental threat, it can also impact on the profitability of sheep farming," Dr Obendorf said. "DFT is causing significant population decline in devils and we've lost our top order marsupial predator that was probably responsible for maintaining a balance on feral cats, since devils probably predated their kittens."

Toxoplasmosis has long been a focus for Tasmania. The late Barry Munday, a former veterinary pathologist at Launceston's Mt. Pleasant laboratories, did a masters thesis on the disease during the 1960s, prompted by his concern about increased abortion rates in sheep. "He began a broad and ambitious venture surveying for toxoplasma in native animals, domestic animals and humans that used the technology of the day," Dr Obendorf said. "When I joined the department in 1980 I took on some of that work and started to investigate the impact of toxoplasmosis on wildlife."

Results from subsequent studies conducted in the last 25 years have confirmed that a range of native animals are susceptible to toxoplasmosis. In areas in which the disease was confirmed, it caused sickness and death in wild animals. "When we did the pathology we found toxoplasmosis was the cause, so we looked into how the animals were exposed and what made them susceptible to this parasitic infection," Dr Oberndorf said. "In 2000 I began a study on how the threatened eastern barred bandicoot could be infect. This study showed that not only were they extremely susceptible to very low numbers of orally given oocysts, but that earthworms exposed to toxo oocysts - one of their major food sources - act as paratenic or transport hosts for toxoplasmosa to enter their system."

"Another study undertaken with the Nature Conservation Branch of DPIWE involved monitoring two bandicoot populations for three years, and blood tests showed how toxoplasmosa caused one population to crash absolutely as an autumn die-back," Dr Obendorf said.

A combination of weather stress, nutritional stress and the availability of the organism in the soil are important factors needed for bandicoots to contract the disease.

Tasmania's cool, temperate climate allows the toxo oocysts to survive in bushland or in grasslands and pasture - places where feeding animals are likely to be exposed - for 12 - 18 months. They can also be dispersed across a wide area through constant movement of slugs, snails, earthworms and copraphagic beetles and other insects that act as mechanical spreaders or as paratenic hosts.

Although cats are essential for the life cycle to be completed, birds, mammals and marsupials can all act as hosts, allowing organisms to establish an intermediate stage within the host's tissues. Cats complete the cycle when they consume these intermediate host stages.

From his collaborative work in the mid-1960s with world toxoplasmosis expert J P Dubey, Dr Munday established the increasing abortion rate in sheep was associated with the exposure of previously unexposed maiden ewes to toxoplasmosa oocysts during their first pregnancy.

Their work highlighted the emerging threat toxoplasmosis could be for domestic animals like sheep, goats, pigs and humans.

But its potential as a public health issue is the reason he wants toxoplasmosis to be a notifiable disease. Compared with several European countries, where pregnant women are automatically screened during their first trimester, and given information about the risks involved with cat contact, concen about the diease in Australia is relatively low.

"On the national agenda feral cats are considered to be one of the threatening processes for about 40 endangered species of wildlife. Predation is one way cats can kill, but for some species toxoplasmosis is also part of that threat.

For people a high exposure risk is through contact with cat faeces or their residue. This is why sandpits, compost bins, gardens and wherever cats defecate, can be high risk sources of infection," Dr Obendorf said.

Anne Layton-Bennett