This patient was diagnosed with hydatid disease or in this case cystic echinococcosis.
Hydatid disease is a parasitic zoonotic disease caused by a tapeworm. Specifically, it is most commonly caused by the cestode, Echinococcus granulosus (commonly called the Dog Tapeworm). There are two other less commonly encountered medically important Echinococcus spp. (E. multilocularis and E. vogeli). This particular case was due to Echinococcus granulosus.
Hydatid disease itself can be insidious in its slow progression and be a potentially serious disease that can be fatal in certain cases. Disease symptoms can take years to appear as the growth of the cyst in the human host is slow. Symptoms begin to appear when the increased size of the cyst produces discomfort or pathology due to organ crowding/involvement. Some species are more specific in their disease presentation such as E. granulosus causing cystic echinococcus and E. multilocularis causing alveolar echinococcus. E. granulosus is the most common of the species and within the E. granulosus sense lato complex there are various genotypes that differ in their distribution, host range and morphological features. It is much simpler to describe it as its own species. E. multilocularis is the most virulent of the three species but rarely encountered. E. vogeli is even more rare.
The treatment of hydatid disease can vary according to the extent of the disease and/or location of the cysts that form in the infected individual. Treatment can consist of a combination of antiparasitic therapy and surgical cyst resection, or the percutaneous aspiration and instillation of scolicidal agents. There are a variety of scolicidal agents that can be used and many are not without unwanted side effects. Hypertonic saline, silver nitrate, ethanol and hydrogen peroxide are examples. These agents have the unfortunate side effect of developing sclerosing cholangitis in the postoperative period. Scolicidals are important in the killing of viable scolices inside the cyst during surgical intervention so as to prevent secondary hydatidosis from occurring. Also, the cyst contents are critically important to contain as the release of the contents can induce a fatal anaphylactic reaction in the patient.
The adult worms are relatively small, at 2-7mm long. The adult worms are going to be seen only in the small intestine of the definitive host (Dog / canids) and not in the intermediate host (sheep or other ruminants) or human accidental host. The photo below is a that of an adult worm.
Shown below is a CDC illustration of the life cycle of E. granulosus. As illustrated humans accidentally ingest the embryonated eggs and the cycle essentially results in a dead end as humans are not the definitive host. But as can be seen in the life cycle illustration below, the canids and sheep or ruminants (definitive and intermediate hosts) are critical for the successful completion and continuation of the tape worms life cycle.
tThe image of the object drawn from the cyst in this patient is a protoscolex form. Other developmental structures can be seen many times in this “hydatid sand” contained in the cyst. At about 7 in the image you can clearly see the presence of hooklets.
Complications due to the presence of the growing cyst around critical organs (liver, lung, brain) are of concern. Spillage of the cyst contents from rupture or surgical procedure can result in anaphylactic shock and/or further spread or secondary hydatidosis as mentioned before.
The importance of not feeding dogs organ meat or “offal” is especially important in the prevention of controlling the prevalence of echinococcus infections in humans. This is especially true in areas where sheep are raised and offal is given to dogs as food. It is these organ meats that contain the cysts to be spread to the definitive dog host and therefore allow the cycle to continue.
Echinococcus can be found globally in every continent except for Antarctica. In the United States it is mostly found in the SouthWest and Alaska. Higher amounts of the disease are seen in the Mediterranean, China, Australia, South America, Russia, and North/East Africa.
Hope you enjoyed this case study and review on Echinococcus. If you’d like more information please use the following CDC link:
https://www.cdc.gov/dpdx/echinococcosis/index.html