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

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.

Keywords: Echinococcus; Eg95; Indigenous people; echinococcosis control; hydatid cyst; ovine; vaccine; zoonosis.

Figure 1

(a) Map of Chile with administrative regions. (b) Map of the Biobío region and its location in Chile. (c) Map of the Alto Biobío commune, with its location in the Biobío region; the main rivers and localities that participated in assessments of the Eg95 vaccination program are shown.

Figure 2

(a) Hydatid cysts in the lung and liver of sheep (arrow). (b) Protoscolex of Echinococcus granulosus s.l. extracted from a large hydatid cyst. Alto Biobío, 2020.

Figure 3

Small hydatid cyst extracted from sheep liver and lungs (hematoxylin-eosin (H&E) stain). (a) The three characteristic layers of the cyst and amorphous deposits stained dark violet with H&E, concordant with calcium deposits. (b) Granulomatous inflammation with the presence of multinucleated giant cells and some eosinophilic polymorphonuclear leukocytes. (c) Miliary pattern of multiple coalescing cysts with a peripheral granulomatous inflammatory response. (d) Granulomas with detritus in the center and a peripheral adventitial layer. Alto Biobío, 2020.