Praziquantel treatment of dogs for four consecutive years decreased the transmission of Echinococcus intermedius G7 to pigs in villages in Lithuania

Abstract

Echinococcus granulosus sensu lato comprises a number of recognized species which cause cystic echinococcosis (CE) in humans and intermediate hosts. These species have particular geographic distributions, with E. granulosus sensu stricto (genotypes G1/2/3 and micro variants) being most widely spread. In Lithuania, E. intermedius (G7) is known to be the only species circulating between pigs and dogs but is also infecting cattle and humans. In fact, recent reports showed a rise of the incidence to 1.13 human cases/100,000 inhabitants/year. Most of the pigs reared on the backyard farms in Lithuania are slaughtered on site during the cold season (October-April) and are used for own consumption. Therefore, in this study, we examined the impact on taeniid transmission of treating dogs with baits containing an oral formulation of praziquantel every two months during the pig slaughtering season in endemic villages in Lithuania. This study started in November 2006 and ended in January 2011; the first dog treatment was administered in February 2007. The results show that the prevalence of E. intermedius, E. multilocularis and Taenia spp. decreased significantly in treated dogs from the second year of the study when compared to untreated dogs. The treatment of dogs also had an impact on reducing the incidence of CE in fattener pigs from 17.6% (2006-2007) to 3.8% (2008; P < 0.05) and in sows from 26.9% (2006-2007) to 3.6% (2008), and eventually to zero in 2010 (P < 0.05) in fatteners and sows as compared to animals from "control" areas (30.7% and 63.7%, respectively). The results document a significant decrease in the transmission of E. intermedius (G7) after treatment of dogs with praziquantel in a relatively short time on farm level in Lithuania. Taeniid prevalence in dogs remained low in 2017 in the areas where anthelmintic intervention was performed until 2010 and, surprisingly, it was also strongly reduced in control areas. Reduction of taeniid transmission is likely associated with a decrease in the number of dogs in the villages as well as an overall decline in backyard pig farming after 2014 due to the outbreaks of African swine fever in Lithuania.

Keywords: Control; Cystic echinococcosis; E. granulosus; E. intermedius; G7; Praziquantel.

Fig. 1

The prevalence of E. intermedius, Taenia spp. and E. multilocularis in control (A) and praziquantel treated (B) dogs examined in December of each year. Results are based on taeniid egg isolation and molecular identification (Trachsel et al., 2007). All dogs were treated with praziquantel at the last sampling in 2010, thus the data for 2017 represent comparable populations of dogs. Vertical bars represent 95% confidence interval. * significant reduction as compared to the control group in the same year (p < 0.05); ** before the first treatment.

Fig. 2

The annual incidence of cystic echinococcosis in all pigs investigated, in fatteners and in sows from control areas (A) and areas with anthelmintic intervention starting in December 2006 (B) according to post-mortem examination of carcasses from pigs slaughtered during the whole year. *significant reduction as compared to respective pigs from control areas in the same year (p < 0.05) or other group of pigs in the same year ^∋ (p < 0.05); ** data collected in period between November 2006 and December 2007.

Fig. 3

The annual incidence of developing, fertile or degenerating E. intermedius cysts in fatteners (A) and sows (B) from control areas and in fatteners (C) and sows (D) from areas with anthelmintic intervention. Vertical bars represent 95% confidence interval. * significant difference as compared to pigs from control areas in the same year (p < 0.05) or degenerating cysts in the same group within the same year ^∋ (p < 0.05).