NTDs: Echinococcosis – a prime example of domestic animal-mediated zoonoses

This post is the 5th in a series highlighting the WHO’s list of 17 Neglected Tropical Diseases (now technically 18 as mycetoma was added to the list at the 69th World Health Assembly in May 2016). To read the previous posts in this series click here.

Echinococcus granulosus (a tapeworm). Courtesy CDC.

This new post is on Echinococcosis. If you’re anything like me you read the previous sentence and thought “on what?”. Here is one of the poster children for the “neglected” part of neglected tropical diseases. While I am by no means a global health expert, I like to think that I’m relatively in-the-know on global health issues, but I had never even heard of this NTD before. Here’s what I learned so that next time someone mentions Echinococcosis you can say you’ve at least heard of it before.

Echinococcosis is a parasitic disease caused by some rogue tapeworms, Echinococcus granulosus and E. multilocularis. These wayward tapeworms cause two types of echinococcosis, cystic (also called hyatidosis) and alveolar, respectively. Both diseases are characterized by long asymptomatic periods of incubation that can last many years before clinical symptoms emerge. Once those symptoms emerge these unruly tapeworms can cause serious morbidity and even death. These errant tapeworms like to make their homes in the liver and lungs of humans, among other organs.

You might be asking why I keep referring to these tapeworms as rogue, wayward, errant and so forth, it’s because humans are not their natural host.

Life cycle of Echinococcus

Life cycle of echinococcus. Courtesy CDC.

In a perfect world, humans wouldn’t even become infected with these tapeworms. The ones that cause cystic echinococcosis normally infect sheep, dogs, and occasionally other livestock like goats, swine, horses, etc. The worms that cause alveolar infect wildlife like foxes, other carnivores, and rodents. Even our friendly domestic dogs and cats can be infected and contribute to the infection of humans. For both diseases, humans become infected through the ingestion of soil, water, food (vegetables, berries, etc.) contaminated with the parasite’s eggs, and also through hand-to-mouth transfer from a contaminated dog’s fur for example.

Around the world over 1 billion people are affected by echinococcosis at any one time with a high risk of contracting it in rural endemic areas. Cystic echinococcosis is basically globally distributed, with highly endemic areas mostly found in the eastern part of the Mediterranean region, northern Africa, southern and eastern Europe, at the southern tip of South America, in Central Asia, Siberia and western China. Conversely, alveolar echinococcosis is restricted to the northern hemisphere, in particular to regions of China, Russia and countries in continental Europe and North America.

Echinococcus distribution 2011. Courtesy WHO.

Cystic echinococcosis distribution 2011. Courtesy WHO.

So what we can do about it? Well not much actually. Treating echinococcosis is expensive and complicated to treat, sometimes requiring surgery or prolonged drug treatment. To prevent human disease in the first place the world needs de-worming programs, improved slaughtering hygiene to prevent contamination and public education campaigns. Vaccination of livestock is also another option. It costs around US$ 3 billion each year to treat cases and provide livestock industry compensation. According to the WHO, a program including vaccination of lambs, de-worming of dogs, and culling of older sheep could lead to the elimination of human cystic echinococcosis in less than 10 years. Preventing the alveolar version is a little more challenging as it involves wild animals.

So there you have it. Now you know about another NTD: echinococcosis. Go forth and impress all your friends with your new knowledge.

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