Echinococcosis Overview

As a neglected tropical disease, Echinococcosis is a lesser-known infectious disease that largely affects the poorer subpopulations of the world. Impacting over one million people, Echinococcosis is widespread and deserving of more attention than it currently receives. The disease can be found in two main forms: Cystic Echinococcosis (CE) and Alveolar Echinococcosis (AE). The disease can be best understood by understanding its three main components: agent, host and environment.

Agent:

Both forms of Echinococcosis are helminthic; the disease itself is caused by worms entering the human body. The helminths are both part of the genus Echinocococcus, a subdivision of the phylum Cestoda. As cestoda (commonly known as tapeworms), the helminths appear flat and both genera are fairly singular biologically. However, key differences are found in the epidemiology and pathology of the two different forms of Echinococcosis.

Cystic Echinococcosis

       Caused by larvae of the Echinococcus granulosus tapeworm and also known as hydatid disease, Cystic Echinococcosis is often asymptomatic. These Echinococcus granulosus eggs are able to survive harsh conditions such as snow and freezing temperatures, and often mature in dogs. The worm, which grows to two to seven millimeters at full length, can also be found in other livestock breeds — namely sheep, cattle, goats, and pigs — but is only uses these animals as intermediate hosts (whereas dogs are definitive hosts for the Echinococcus granulosus).

 

 

       Echinococcus granulosus worms can be found throughout the world, in Africa, Europe, Asia, the Middle East, and Central and South America. However, the abundance of the helminth is very much dependent on the amount of sheep being raised by the local population, and the population of dogs in the area.

Alveolar Echinococcosis

Caused by the larval stage of the Echinococcus multilocularis tapeworm, Alveolar Echinococcosis differs significantly from its counterpart CE. The Echinococcus multilocularis worms are shorter in length, ranging between one and four millimeters, and are primarily found in northern areas of the world. However, the worm is still fairly widespread, calling northern  Europe, Russia, China, Central Asia, Japan, and North America home.

The hosts of Echinococcus multilocularis also vary significantly from those of Echinococcus granulosus. While both are found in dogs, definitive hosts for the multilocularis species also have definitive hosts in foxes, coyotes, and domesticated dogs and cats. The list of intermediate hosts for the tapeworm includes many species of small rodents.

Host:

While intermediate hosts play important roles in the transmission and understanding of both CE and AE, the human form of the disease is crucial in understanding Echinococcus’s status as a neglected tropical disease.

 

bigstock-tapeworm-67198201-747x560

Mature worm attaching itself to the liver

The two main forms of the disease impact humans differently.

  • Cystic Echinococcus is largely asymptomatic and creates cysts in the human body, primarily in the liver and lungs. These cysts grow and become painful over time, and are often unnoticed (and therefore neglected and untreated) for years. Any observed symptoms are usually caused by cysts restricting and interacting with other parts of the body; these include: pain or discomfort in the upper abdominal region or chest, nausea, vomiting, or coughing may occur as a result of the growing cysts, are usually caused by cysts restricting and interacting with other parts of the body. Cysts also lyse and leak, which could create bacterial infections, abscesses or immune reactions within the body. The main treatment for Cystic Echinococcus is surgery to remove the cyst. Alternate treatments, namely medication and an aspiration surgical procedure, are being developed but their effectiveness is still being questioned.

  • Alveolar Echinococcus has a much harsher impact than CE, and — although less common — is much more fatal. The larvae form many cysts which become mestocodes, continuously growing tumorlike masses that are not clearly separated from host tissues. Alveolar Echinococcus is able to stay in a presymptomatic phase for years before the host develops symptoms, but the symptoms come quick and fast. Often infecting the liver, lungs, brain, and bones, the larvae grow from tumorlike buds into multiple lesions (warning: graphic image). The mestocodes formed also result in severe fibrosis throughout the infection period, compressing and obstructing major vessels and bile ducts throughout the human body. Similarly to CE, surgery is the only viable treatment for Alveolar Echinococcus, needing to remove the whole parasitic mass and then medicate the host in order to prevent the cyst from growing back.
echinococcus_lifecycle

Diagram outlining the progression of Echinococcus in the human body

Environment:

Because all forms of Echinococcosis are zoonotic (transmitted to humans from animals), humans can only be called accidental intermediate hosts, meaning we become infected in the same way as all other intermediate hosts, but are not able to transmit the disease. Humans do not excrete the eggs of the disease, and only become infected by ingesting food or water contaminated with faeces of animals which have been infected with the tapeworm. The location and abundance of these animals, the various definitive hosts mentioned above, largely dictate the spread of Echinococcosis and the number of people that fall ill with the disease.

global_distribution

Map showing the endemic regions of Echinococcosis: it is an incredibly widespread disease.

While treatment often requires surgery, preventing Echinococcosis is a much more straightforward and simple process. According to the CDC, the best ways to prevent CE are:

  • Limiting the areas where dogs are allowed and preventing animals from consuming meat infected with cysts. You should:
    • Prevent dogs from feeding on the carcasses of infected sheep.
    • Control stray dog populations.
    • Restrict home slaughter of sheep and other livestock.
    • Not consume any food or water that may have been contaminated by fecal matter from dogs.
  • Washing your hands with soap and warm water after handling dogs, and before handling food.
  • Teaching children the importance of washing hands to prevent infection.

And AE is best prevented by:

  • Avoiding contact with wild animals such as foxes, coyotes, and dogs and their fecal matter and by limiting the interactions between dogs and rodent populations. You should:
    • Do not allow dogs to feed on rodents and other wild animals.
    • Avoid contact with wild animals such as foxes, coyotes and stray dogs.
    • Not encourage wild animals to come close to your home or keep them as pets.
  • Washing your hands with soap and warm water after handling dogs or cats, and before handling food.
  • Teaching children the importance of washing hands to prevent infection.

If you are worried that you might have Echinococcosis, check information from the CDCWHO or Healthline to understand the symptoms and diagnoses. Be in contact with your doctor for possible treatment.

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One thought on “Echinococcosis Overview

  1. Pingback: E. Granulosus: the Pathological Agent of Cystic Echinococcosis | Haverford Global Impacts

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