Parasitoses and zoonoses: Echinococcosis and Cystic Hydatidosis

By Cristiano Antonino On Nov 11, 2022

Echinococcosis is a parasitic disease caused by the echinococcus (Echinococcus granulosus), a small flatworm belonging to the tenidae family

The adult parasite attacks the intestines of dogs and, more generally, canids, which are the main carriers of the disease and are therefore called ‘definitive hosts’.

Intermediate hosts are instead defined as man and other animal species (sheep, cattle, pigs, other wild mammals, etc.) that are particularly susceptible to contracting this infection.

The greatest spread of this disease has been found in areas dedicated to pastoralism.

For the infection to spread, it is in fact necessary for a definitive host, in which the disease is mostly asymptomatic, to feed on an intermediate host (think of dogs that tend flocks and easily come into contact with the remains of other animals), reactivating the parasite’s life cycle.

Echinococcosis and Cystic Hydatidosis: the parasite and its life cycle

The echinococcus has a head covered with many hooks, while the remaining three body portions, of varying size, grow over time.

The hooks on the head are used by the parasite to anchor itself to the walls of the dog’s intestine.

Once anchored, this worm divides in a relatively short period of time, leaving the last part of its body, the one full of eggs, to be excreted by the host through defecation.

The eggs spread in the surrounding environment, water or soil, and are quite hardy.

Once ingested by an intermediate host, they initiate the parasite’s life cycle: they hatch and release a larva in the stomach of the host organism that enters the bloodstream, from where it can potentially reach any of the organs.

However, usually the larva stops in the liver or lungs, more rarely it affects the brain or kidneys.

It is precisely this stage of the parasite’s life that gives its name to the disease that affects humans and animals: cystic hydatidosis.

The larva, in fact, upon reaching an organ settles there and forms a cyst, the size of which gradually increases over time, in which many other larvae of the parasite will form and multiply (the size and position of the cysts in the organism determine the danger).

Echinococcosis and Cystic Hydatidosis, how echinococcus is transmitted

Man, as already mentioned, is an intermediate host organism, i.e. an organism in which infection causes the formation of these cysts (which can reach a considerable size).

Contamination of humans is caused by ingesting the parasite’s eggs excreted by the dog: by eating contaminated food, using contaminated water or by direct contact with the infected dog (the animal’s saliva or hair could spread the disease).

Therefore, elementary hygiene rules remain of paramount importance:

wash your hands thoroughly after coming into contact with a dog (especially beware of stray dogs)
pay attention to the hygiene of children (who very easily bring their hands to their mouths)
wash foodstuffs such as vegetables and fruit thoroughly
avoid contact with contaminated water
have your dog checked regularly (in which the infection is in most cases asymptomatic or manifests itself as intestinal irritation)

How echinococcosis and cystic hydatidosis manifest themselves

Echinococcosis does not present itself with any particular symptoms in humans.

At an early stage, cystic hydatidosis may be asymptomatic and may continue to be so for several years.

Only when its size increases is its presence sometimes denounced by abdominal pain, obstruction of a bile duct or, when its size is considerable, it can be felt by palpating the affected area.

If the cyst has formed in the lung, coughing and/or chest pain may occur.

A large cyst (it can reach the size of a fetus) can put pressure on surrounding organs and tissues, damaging them or causing them to malfunction.

The integrity of the cyst is also a determining factor.

If it were to rupture, spillage of the fluid it contains could cause an anaphylactic reaction in the host organism, leading to its death, or spread the larvae and thus result in the birth of multiple other cysts.