Neglected tropical diseases

WHO Informal Consultation on echinococcosis recommends vaccination of animals to prevent human transmission

Field trials may target dogs and livestock

25 June 2011 | Geneva


An Informal Group on Echinococcosis has recommended field trials of a newly developed vaccine to control and prevent transmission of echinococcosis from animals to humans. Experts believe that two forms of this parasitic disease affects more than one million people worldwide at any time.

Cystic echinococcosis (CE) and alveolar echinococcosis (AE) in their larval stage develop into cysts in humans capable of causing substantial morbidity and suffering. Participants also reviewed the situation in northern and eastern Africa, the Mediterranean area, Latin America, Central Asia and Western China. Both forms of the disease are intrinsically tied to impoverished settings in the tropical world where they primarily affect poor livestock keepers and their families, perpetuating the circle of poverty.

"Advanced cases of cystic echinococcosis and alveolar echinococcosis are serious health threats. Treating both these conditions often requires surgery and/or prolonged use of medicines for affected individuals" said Dr Phlip Craig, Chair of the Consultation on Cystic and Alveolar Echinococcosis, held at WHO Headquarters in Geneva from 23-24 June 2011, "In the case of alveolar echinococcosis, the disease is fatal if untreated".

Cystic echinococcosis is a preventable disease. Suitable interventions such as treating dogs regularly, carrying strict controls during the slaughter of livestock, destroying infected offals and public education have shown that transmission can be stopped in different settings in developed countries.

Participants to the Informal Consultation however argued that the success of highly intensive intervention programmes in developed countries may not work in low or middle income countries, where much of the disease burden occurs.

The Consultation assessed results obtained from a recently developed vaccine against cystic echinococcosis in sheep and identified potential countries where well-controlled efficacy and feasibility studies could be conducted. Potential candidate countries identified by the Consultation are Kyrgyzstan, Peru and Tunisia.

"The Consultation proposes alternative strategies involving the vaccination of sheep in addition to classical interventions" said Dr Lorenzo Savioli, Director of the Department of Control of Neglected Tropical Diseases. "It is time to initiate definitive field trials as this could provide a much higher chance of success in CE affected countries."

Human echinococcosis is usually caused by larval stages of Echinococcus granulosus or Echinococcus multilocularis. The life cycle of E. granulosus involves the dog in which the adult tapeworm is a harmless intestinal infection and a number of farm animals particularly sheep in which a hydatid cyst develops. Humans are infected through direct or indirect contacts with the faeces of an infected dog containing eggs from the parasite.

E. multilocularis is a parasite of wildlife: foxes are the definitive host and small mammals such as rodents are the intermediate hosts. Dogs can also be infected from rodents. Humans become infected from they come in contact with eggs found in the faeces of foxes and occasionally dogs.