In the days when Britain ruled the waves and its colonies, some sheep from Thomas Hardy’s Wessex and other counties followed their masters to the antipodes instead of stupidly jumping off a cliff.¹ They multiplied in the sun and produced much wool, some of which was later returned to England under the imperial preference system and sent back to all corners of the British Empire as manufactured products such as jackets or coats, so that preindustrial Australia was said to have been built on the backs of the sheep. However, infected sheep and sheepdogs constituted a potential risk to humans. Professors, who had often come from the same place as the sheep, studied the problem and wrote books which the students were expected to buy.

The students would thus learn that the danger came from a parasitic tapeworm of the genus Echinococcus, small, about 2–7 mm long, consisting of three segments or proglottids, of which the gravid segment could hold 1,000–5,000 eggs. Complex illustrated charts indicate that the adult tapeworm lives in the small intestine of its definitive host, classically a sheepdog or another dog, but potentially a fox, wolf, or coyote. Firmly attached to the mucosae of their small intestines, the worm sheds myriads of these eggs that can be ingested by various ruminant herbivore intermediate hosts, generally sheep and humans. In the small intestine of infected humans, the worms can release small living things that pass through their host’s intestinal wall into the circulation and form hydatid cysts in the lungs, liver, or elsewhere.

Currently, E. granulosus resides in the intestines of 2–3 million people worldwide, causing over 200,000 new clinical cases each year, damaging the livestock industry and inflicting significant economic losses by reducing meat, milk, and wool production. Symptoms depend on the location of the hydatid cysts and on what pressure they exert on adjacent tissues. The disease has occurred in humans for at least 8,000 years, but its animal origin was not recognized until 1684, followed by a description of the hydatid cysts and the tapeworm.

In 1853, Carl von Siebold identified the worm as causing the disease in humans, and in 1863, Bernhard Naunyn demonstrated the role of dogs in its transmission. In 1901, Bernhard Nocht developed a complement fixation test for diagnosis, an advance followed by improved surgical techniques for removing the cysts and the introduction of albendazole and mebendazole for treatment. Efforts to control the disease have focused on interrupting the transmission cycle between dogs and livestock and educating communities about the importance of proper hygiene and the safe disposal of infected animal carcasses. Vaccination of livestock has also been explored as a potential control measure. Despite these advances, hydatidosis remains a significant public health problem in many parts of the world, particularly in rural areas where there is close contact between humans, dogs, and livestock, such as in some parts of Mediterranean countries, South America, Australia, New Zealand, Central Asia, and Africa.

Note

1. Thomas Hardy. Far from the Madding Crowd, 1874.