Pilot field trial of the EG95 vaccine against ovine cystic echinococcosis in Rio Argentina: second study of impact

EDMUNDO LARRIEU; GUILLERMO MUJICA; CHARLES GAUCI; KATHERINA VIZCAYCHIPI; THELMA VERONICA POGGIO; MARSHALL W. LIGHTOWLERS

Bucarest

Congreso; ? XXVIth World Congress on Echinococcosis - Cystic and Alveolar Echinococcosis: Old Diseases - New Challenges In conjunction with the IInd National Conference of chinococcosis; 2015

International Association of Echinococcosis Romanian Association of Hydatidology ?Carol Davila? University of Medicine and Pharmacy ?Colentina? Clinical Hospital

Cystic echinococcosis is endemic in the Rio Negro provinceof Argentina. After 30 years of control using praziquantelin dogs the transmission rate to humans and sheephas decreased significantly, however transmission persists.The objective of the study was to assess the impact ofthe inclusion of the EG95 vaccine for sheep in the controlprogram. The vaccine was applied in an area comprisingcommunities of native people. Two different groups wereassigned to different treatment types. One group comprising71 farmers of Blancura Centro and Lipetren regionswas established as the control region where no vaccinationswere undertaken. In the treatment group, comprising79 farmers of Anecón Grande, Mamuel Choique, NahuelPan and Rio Chico abajo regions, lambs received two vaccinationswith the EG95 vaccine followed by a single boosterinjection when the animals were 1-1.5 years of age. Theprevalence of CE in sheep in vaccinated area at the startof the trial (2009) was determined by ELISA/Westernblotas being 26.2% in 2-4 tooth animals. In 2011 7.8% of the2-4 tooth age class were positive (p=0.006 between 2009and 2011). In relation with the farmers in 2009 80.0%had at least one animal positive to ELISA/Westernblot inthe 2-4 tooth age class and 42.8% in 2011. Evidence forEchinococcus granulosus transmission was monitored bynecropsy on adult sheep in 2015. A total of 21443 doses ofEG95 vaccine were applied in the period 2009-2015. Beforethe vaccine was introduced, 56.3% of 6-year-old animalswere positive at necropsy. The prevalence decreased to21.1% in 6-year old animals following use of the vaccine.The number of cysts per infected animal also decreasedfrom 1.4 to 0.3. Despite the difficulties of implementingvaccination in this region of Rio Negro and 47% of theanimals being fully vaccinated in the mong those that wereassessed by necropsy, the EG95 vaccine achieved a 62.5%reduction in infection in 6 year old animals. Nevertheless,this trial has demonstrated the EG95 vaccine is a valuabletool to assist with reducing E. granulosus transmission,even in circumstances where delivery of the programfaces many practical difficulties. In the future it will beimportant to demonstrate the effect of sheep vaccinationon transmission to dogs and hence the likely effects ontransmission of CE to humans.