Assessment of the Vaccination Program against Cystic Echinococcosis in Sheep in the Pehuenche Community of Central Chile

SIMPLE SUMMARY: Cystic echinococcosis is a parasitic disease affecting humans; in Chile, it uses sheep and dogs as its main hosts. The Eg95 vaccine has been developed with the aim of controlling ovine infection. Here, we present the results of a 3-year control program in the Alto Biobío commune in central Chile. The program tried to provide a first dose at 2 months of age, a booster 1 month later, and yearly vaccination. Given the difficult land work, important delays in the vaccinations were recorded, and many animals did not receive the first booster. Dog deworming was not included in the program. The main results of the program were that after vaccination, the proportion of large and fertile cysts was lower than before; however, the proportion of infected sheep had not reduced. In addition, the lower age at first dose and the administration of the second dose 1 month after the first were associated with greater protection. Hence, the results suggest that vaccination was not effective against the infection of sheep, but it was effective against the development of cysts; thus, cysts are less infective for dogs. This could favor disease control by cutting the cycle. ABSTRACT: Echinococcosis is a neglected zoonosis that uses dogs and sheep as its main hosts in Chile. The Eg95 vaccine against sheep infection has been included in some control programs. Here, we assess the efficacy of the vaccination program in the hyperendemic Alto Biobío commune after 3 years of execution. Fisher’s test and generalized linear models were used in the assessment. The program tried to offer a first dose at 2 months of age, a booster 1 month later, and yearly vaccination. Given logistic difficulties, important delays in vaccination occurred, and most animals did not receive the first booster. Dog deworming was not included in the program. Likely due to the aforementioned factors, the overall frequency of infection was not lower, but the proportion of large (>5 mm) cysts and fertile cysts was smaller after the program. The frequency of infection and/or the number of cysts were lower when the age at first dose was younger and the first booster was administered 1 month after the first dose. The results suggest that vaccination affects both cyst development after the larvae reach the target organs, as well as the development of the protoscolex once the cysts start developing.