Pilot Field Trial of the EG95 Vaccine Against Ovine Cystic Echinococcosis in Rio Negro, Argentina: Second Study of Impact

Abstract

BackgroundCystic echinococcosis (CE) is an important zoonotic disease caused by the cestode parasite Echinococcus granulosus. It occurs in many parts of the world where pastoral activities predominate, including the Rio Negro province of Argentina. Although CE control activities have been undertaken in the western regions of Rio Negro for more than two decades, the disease continues to remain prevalent in both the human and livestock animal populations. Vaccination of animal intermediate hosts of CE with the EG95 vaccine may provide a new opportunity to improve the effectiveness of CE control measures, although data are lacking about field application of the vaccine.AimsEvaluate the impact of EG95 vaccination in sheep on the transmission of Echinococcus granulosus in a field environment.MethodologyTwo trial sites were established in western Rio Negro province within indigenous communities. Vaccination of lambs born into one trial site was introduced and continued for 6 years. Prior to initiation of the trial, and at the end of the trial, the prevalence of CE in sheep was determined by necropsy. Weaned lambs received two injections of EG95 vaccine, approximately one month apart, and a single booster injection one year later. Vaccination was not implemented at the second trial site. A total of 2725 animals were vaccinated in the first year. Animals from this cohort as well as age-matched sheep from the control area were evaluated by necropsy.Key resultsIntroduction of the vaccine led to a statistically significant in the number and size of hydatid cysts in comparison to the situation prior to the introduction of the vaccine, or compared to CE prevalence in the control area where the vaccine was not applied. The prevalence of infection in the vaccinated area was also significantly reduced by 62% compared to the re-intervention level, being lower than the prevalence seen in the control area, although the difference from the control area after the intervention was not significant possibly due to limitations in the numbers of animals available for necropsy.ConclusionsVaccination of sheep with the EG95 vaccine provides a valuable new tool which improves the effectiveness of CE control activities. Vaccination was effective even in a difficult, remote environment where only approximately half the lambs born into the communities were fully vaccinated.

Control of cystic echinococcosis: Background and prospects

“…That vaccination programme in Rio Negro, Argentina, began in December 2009, and an evaluation of the impact was undertaken using serological methods in 2012 (Larrieu et al, ) and using necropsy of old sheep in 2015 (lambs vaccinated in 2009) (Larrieu et al, ). In the vaccinated group, four sheep showed six hydatid cysts, all of which were small (1 × 1.3–0.2 × 0.2 cm in diameter); two cysts were found in the liver (only one was fertile) and 4 in the lung (average 0.3 cysts per animal).…”

“…Statistically significant difference was demonstrated in the number of cysts between control group and vaccinated animals ( p = .02). Regarding to the farms, 94.7% had at least one positive animal by necropsy in 2009, whereas only 23.5% of them were positive in 2015 (Larrieu et al, ). Using coproELISA for diagnosis of infection in dogs, the differences were statistically significant ( p value = .04) between baseline (2009) and impact (2017) studies in the proportion of positive samples, and in relation to the farms, the differences were not significant among producers with farms with active transmission (by the presence of an infected dog; p value = .1) (Larrieu, Mujica, et al, ; Larrieu, Uchiumi, et al, ).…”

“…Although the EG95 vaccine has demonstrated a high efficacy, there have been few studies that have evaluated the effectiveness of the vaccine under field conditions (Larrieu, Mujica, et al, ; Larrieu et al, ; Larrieu, Uchiumi, et al, ). Additional studies of vaccination are required; for example, it is necessary to look for different vaccination schemes (only lamb vaccination, whole sheep population vaccination); also, animal species involved in the vaccination programme (bovine, goats, pigs and camelids) considering costs of the vaccine and the costs of its placement in the field.…”

Transcriptome profiling of gene expression during immunisation trial against Fasciola hepatica: identification of genes and pathways involved in conferring immunoprotection in a murine model

“…Developing an effective vaccine represents one of the most appealing strategies for preventing this disease and reducing the risk of infection in humans. No commercial vaccines are yet available for F. hepatica although significant progress has been made regarding attempts at developing effective vaccines against infection caused by other parasites, only a few vaccines have been successfully tested against helminthic infection in animals [21–24]. Several antigens have been identified and tested as vaccine candidates against F. hepatica infection.…”

Serology and longevity of immunity against Echinococcus granulosus in sheep and llama induced by an oil‐based EG95 vaccine

“…Furthermore, the EG95 vaccine demonstrated a high level of protection of both sheep and goats under field conditions in China when it is used as an additional control tool. The evaluation of the outcomes of vaccination in field trials performed in Argentina revealed a significant 62% decrease in the prevalence of hydatid infection in sheep vaccinated over a 6‐year period. In previous trials in Argentina including sheep and goats, one vaccine dose of a laboratory‐made inclusion body vaccine showed 82% protection after 12 months, whereas two vaccine doses protected 98% after 11 months .…”