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A Social Issue Neglected Tropical Diseases and Three Major Infectious Diseases

Echinococcosis

Infection with tiny tapeworms of the genus Echinocococcus (either Echinococcus granulosus or Echinococcus multilocularis) is the cause of unilocular and alveolar echinococcosis, respectively. The eggs of these parasites are found in the feces of definitive hosts (usually dogs and foxes). Once inside the human host’s body, the oncosphere hatch from eggs, and invade into intestinal tissues, resulting growth of hydatid cyst (also called a echinococcus) and begin to cause various disorders, mainly in liver, after a lengthy asymptomatic period. When left untreated, alveolar hydatid cyst due to E. multilocularis can further cause death. Fatality rates by unilocular hydatid cyst by E. granulosus, on the other hand, are comparatively very low. There may be more than one million people living with either form of this disease worldwide.

Causes of Infection

Disease Agent

Echinococcus

<Microscopic view of adult echinococcus in a dog’s body> CDC

Host

Foxes and dogs (definitive hosts), humans (intermediate hosts)

The cause of human echinococcosis (hydatidosis, or hydatid disease) is the ingestion by humans of the eggs containing oncosphere of cestodes (tapeworms) from the genus Echinococcus. When the eggs of these tapeworms in the feces of dogs or foxes are ingested, the oncosphere appears eventually invade into tissue and cyst-like tapeworm larvae, grow in the body and invade the liver and other internal organs, thereby causing multiple symptoms in the individual.
Echinococcus comes in two types: Echinococcus granulosus and Echinococcus multilocularis.

Cystic echinococcosis (CE)

A 2–7 millimeter long tapeworm found in dogs (definitive host) and sheep, cattle, goats, and pigs (intermediate hosts) is the cause of CE. The infection is from the larval stage of Echinococcus granulosus. CE is the most common type of echinococcosis infection in people.

Alveolar echinococcosis (AE)

Small rodents (rats and squirrels) are the intermediate hosts for Echinococcus multilocularis, however AE is caused by infections of the larval stage of Echinococcus multilocularis, a 1–4 millimeter long tapeworm that is usually found in foxes, coyotes, and dogs (definitive hosts).

Symptoms

Cystic echinocccosis (CE)

Infection with CE may not present any symptoms for some years as the cysts can develop very slowly. However, cysticercosis during this asymptomatic period can keep growing in the internal organs, including the liver and/or lungs. This can cause symptoms that include pain or discomfort in the chest or upper abdomen, nausea, vomiting and/or coughing as the cysticercosis continue to develop. Further, allergic reactions or death can be caused by ruptures related to the cyst fluid.

 
Alveolar echinococcosis (AE)

As with the case of CE, AE cysticercosis is slow-growing. For this reason, infection with AE may not present any symptoms for years. Cysts grow through external budding and occasionally metastasize to other internal organs, while AE is asymptomatic. Due to the growth of these cysts, upper abdominal pain or discomfort, weakness, and weight loss can occur. Symptoms may appear that are similar to those of liver cancer and liver cirrhosis, with AE being clinically treated in a similar way to that of a malignant liver tumor.
AE in animals is relatively common, while human infections are rare. AE is a greater health threat to people than CE as it causes similar to malignancies that form in the liver, lungs, brain and/or other organs. AE can also be fatal if left untreated. The mortality rate is thought to be close to 90%.

 

Diagnosis and Treatment

Cystic echinococcosis (CE)

Imaging from X-rays and MRI scans is helpful for finding CE cysts in most organs. Blood tests and immunological tests are also helpful diagnostic tools, but imaging studies recommended as being far more accurate.
In the past, surgery was the only treatment available for CE cysts. In recent years, however, chemotherapy, cyst punctures, and PAIR (percutaneous aspiration, injection of chemicals, and reaspiration) have become additional effective treatments. If surgery is required, additional medication (with anthelmintics such as albendazole and praziquantel) may also be necessary to keep the cyst from relapse.

 
Alveolar echinococcosis (AE)

AE diagnosis requires blood tests that look for antibodies to Echinococcus multilocularis. Surgery is the most common AE treatment. To keep the cyst from relapse after surgery, medication using albendazole or praziquantel may be necessary.

 

Prevention

To avoid infection of both cystic echinococcosis and alveolar echinococcosis:

  • Children need to know how important it is to wash their hands to prevent infection.
  • A veterinarian should be consulted for suspected infections in pets.
  • People should wash their hands with hot water and soap after touching a dog or cat.
Cystic echinococcosis (CE)

In areas where Echinococcus granulosus is reported in sheep or cattle, in addition to the two measures mentioned above, the following precautions should be taken to avoid infection:

  • Do not allow dogs to wander freely or to capture and eat raw mutton (sheep meat), beef, pork, or goat meat.
  • Do not slaughter sheep or other livestock in the home.
 
Alveolar echinococcosis (AE)

When living in an area where Echinococcus multilocularis is known to be present in rodents and wild canines, the following precautions should be taken to avoid infection (in addition to the above two measures):

  • Unless wearing gloves, never handle foxes, coyotes, or other wild canines, whether they are dead or alive.
  • Do not keep wild animals as pets, especially wild canines.
  • Do not allow dogs and cats to roam freely or to capture and eat rodents.
 

Regions at High Risk of Infection

Cystic echinococcosis (CE)

Although CE is found in Africa, Europe, Asia, the Middle East and Latin America, the areas with the highest risk are in those populations that raise sheep. Incidence rates for cystic echinococcosis in endemic regions can exceed 50 cases per 100,000 person-years, with levels as high as 5–10% in parts of South America (Argentina and Peru), East Africa, Central Asia, and China.

 
Alveolar echinococcosis (AE)

Though mostly found in the northern hemisphere, AE occurs worldwide, including in Central Europe, Russia, Central Asia, China, Japan, and North America.

 

Estimated Number of Infected People

Worldwide, more than one million people are currently living with either cystic echinococcosis or alveolar echinococcosis.

Estimated Number of Deaths

Cystic echinococcosis (CE)

About 6.5% of people relapse after intervention that required prolonged recovery, with an average of 2.2% resulting in postoperative deaths for surgical patients. Meanwhile, the estimated fatality rate from CE is estimated to be approximately 2–4%, though the total number of deaths is not known.

 
Alveolar echinococcosis (AE)

Most cases are concentrated in western China, where more than 90% of people infected with alveolar echinococcosis die in cases where the individual does not undergo treatment.

 

Initiatives by Pharmaceutical Companies and NGOs

A WHO (World Health Organization) pilot project is currently selecting three countries where the validation of effective CE control strategies will be developed and implemented by 2018. Once these three countries are identified, priority will be placed on up-scaling interventions to control and eliminate CE using validated strategies.
In those countries affected, WHO is helping to build capacity through medical and paramedical training courses on the clinical management of cystic echinococcosis.

References
WHO- Neglected Tropical Diseases, accessed March 19, 2014,
http://www.who.int/neglected_diseases/mediacentre/factsheet/en/
CDC- Neglected Tropical Diseases, accessed March 19, 2014,
http://www.cdc.gov/globalhealth/ntd/diseases/