Natural Phenomenon: Hydatids
Summary
Hydatids caused the death of a Tasmanian child every few years until 1968. Deaths occurred when a minor injury ruptured a hydatid cyst of the liver.
Details
This infectious disease is caused by a tiny tapeworm, Echinococcus granulosus, an intestinal parasite of dogs. Sheep that swallow tapeworm eggs when grazing on pastures contaminated by dog faeces may develop hydatid cysts in their lungs and livers. Larval worms in the cysts develop into mature worms in the intestines of dogs fed on sheep's offal. Humans in contact with infected dogs can acquire the same cysts. Cysts discovered in time can be removed surgically, but fatal cases are inevitable. In 1966 over half of adult sheep had hydatid cysts, and more than 1 in 8 rural dogs had adult worms. In the 1950s Tasmanian surgeons operated for human hydatid disease about once every week.
In the absence of government action, Tasmanian farmers started a voluntary campaign, modelled on one in New Zealand. This created political pressure for government support, and the Department of Agriculture gained a budget and the team spirit of a joint campaign, which started in 1965. A compulsory dog test replaced the voluntary test and brought in the small residue of unco-operative owners who had missed it. Quarantine came later for properties with infected dogs, and ultimately the property faced quarantine for a single cyst detected in a slaughtered sheep at an abattoir. Eradication was in sight.
The human incidence fell dramatically in all age groups, even the elderly, refuting a belief that age resistance had protected adults. Lung cysts were the first to disappear. Chest surgeons watched in disbelief as the annual flow of new patients with lung cysts dried up, and the last new human case was diagnosed in 1976. Symptomless cysts apparently acquired before 1970 persist in a few old people, but the age distribution shows that human transmission must have stopped in about 1972. In 1996, Tasmania was also declared provisionally free of hydatids in dogs and livestock.
Trevor Beard