Parasite-Echinococcosis

 
Echinococcosis:
It is referred to as hydatid disease or echinococcal disease. It is a parasitic disease that affects humans and other animals such as sheep, dogs, rodents and horses. There are three different forms of echinococcosis found in human, caused by the larval stage s of different species of the tapeworm of genus Echinococcus. The most common form found in human is cystic echinococcosis, caused by Echinococcus granulosus. The second is alveolar echinococcosis, also known as "small fox tapeworm," caused by Echinococcus multilocularis and the third type is polycystic echinococcosis, caused by Echinococcus vogeli. Alveolar and polycystic echinococcosis are rarely diagnosd in humans and are not as widespread as cystic echinococcosis, but polycystic echinococcosis is relatively new on the medical scene. Alveolar echinococcosis is a serious disease that not only has significantly high fatality rate but also has the potential to become an emerging disease in many countries.

Life cycle:
Eggs:Echinococcus eggs contain an embryo that is called an oncosphere or hexcanth. The name of this embryo stems from the fact that these embryos have six hooklets. The eggs are passed through the feces of the definitive host and it is the ingestion of these eggs that lead to infection in the intermediate host.
Larval/hydatid cyst stage: From the embryo released from an egg develops a hydatid cyst, which grows to about 5–10 cm within the first year and is able to survive within organs for years.Cysts sometimes grow to be so large that by the end of several years or even decades, they can contain several liters of fluid. Once a cyst has reached a diameter of 1 cm, its wall differentiates into a thick outer, non-cellular membrane, which covers the thin germinal epithelium. From this epithelium, cells begin to grow within the cyst. These cells then become vacuolated and are known as brood capsules, which are the parts of the parasite from which protoscolices bud. Often, daughter cysts will also form within cysts.

Adult worm:Echinococcus adult worms develop from protoscolices and are typically 6mm or less in length and have a scolex, neck and typically three proglottids, one of which is immature, another of which is mature and the third of which is gravid (or containing eggs).The scolex of the adult worm contains four suckers and a rostellum that has about 25-50 hooks.

Infection cycle: Like many other parasite infections, the course of Echinococcus infection is complex. The worm has a life cycle that requires definitive hosts and intermediate hosts. Definitive hosts are normally carnivores such as dogs, while intermediate hosts are usually herbivores such as sheep and cattle. Humans function as accidental hosts, because they are usually a 'dead end' for the parasitic infection cycle.