Pilot field trial of the EG95 vaccine against ovine cystic echinococcosis in Rio Negro, Argentina: 8 years of work

Abstract

Cystic echinococcosis is endemic in the Rio Negro province of
Argentina. After 30 years of control using praziquantel in dogs,
the transmission rate to humans and sheep has decreased significantly,
however transmission persists

The objective of the study is to assess the impact of the inclusion
of the EG95 vaccine in sheep in the control program.
The vaccine was applied to lambs from communities of native
peoples which included 70 producers (Anecón Grande, Mamuel
Choique, Nahuel Pan y Río Chico Abajo).
From 2009 on, lambs received two doses of the EG95 vaccine
when they were 30 and 60 days of age, followed by a single
booster injection when the animals were 1 year of age. The
transmission of Echinococcus granulosus was assessed through
necropsy in mature sheep, Arecoline test and coproantigen test
in dogs and register of new clinical cases in inhabitants of the
area. A total of 29.323 doses of EG95 vaccine were applied to
lambs in the 2009-2017 period, working with 4 groups of 2 veterinaries
each, covering 83.5% with one doses, 80.1% with two
doses and 85.7% with three doses. Before the vaccine was introduced,
in necropsy of sheep of 6 years old showed that 45.7%
were infected with E. granulosus. The rate decreased to 21.1% in
2006. The number of cysts per animal decreased from 1.4% to
0.3. The number of producers with infected animals decreased
from 84.2% to 22.2%. The humoral response to the vaccination,
in field conditions, showed an increased in antibodies with the
second dose, reaching its maximum after the booster at one year
of age for many years and keeping constant.
In dogs, 4.7% was found positive using arecoline purgation
and 20.3% of the farms were infected using coproantigen test.
The impact assessment showed a 5.6% of dogs positive to the
arecoline test. Only a new case of echinococcosis was detected
in kids with a 10 cm cyst, and its origin was probably before the
vaccination. EG95 vaccine has been effective to prevent the infection
in ovines up to six years of age, in spite of the difficulties
of achieving better coverage. The transmission to dogs and human
beings has to be determined.