Echinococcosis in sub-Saharan Africa: emerging complexity.
ABSTRACT Cystic echinococcosis occurs in most regions of sub-Saharan Africa, but the frequency of this zoonosis differs considerably among and within countries. Especially human cases seem to be focally distributed. A number of environmental and behavioural factors partially explain this pattern, i.e. density of livestock, presence of dogs, uncontrolled slaughter, and hygiene. In addition, the various taxa of Echinococcus spp. are known to differ considerably in infectivity to different host species including humans. Genetic characterizations of isolates, which are necessary to evaluate the impact of this factor - so far done in only a few countries - indicate that the diversity of Echinococcus spp. in Sub-Saharan Africa is greater than on any other continent. The very incomplete data which are available show that sympatrical taxa may infect different hosts, others may be geographically restricted, some life cycles involve livestock, others wild animals. Possible implications of this complexity for public health, livestock economy and conservation are briefly discussed.
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ABSTRACT: Genetic variability in the species group Echinococcus granulosus sensu lato is well recognised as affecting intermediate host susceptibility and other biological features of the parasites. Molecular methods have allowed discrimination of different genotypes (G1-10 and the 'lion strain'), some of which are now considered separate species. An accumulation of genotypic analyses undertaken on parasite isolates from human cases of cystic echinococcosis (CE) provides the basis upon which an assessment is made here of the relative contribution of the different genotypes to human disease. The allocation of samples to G-numbers becomes increasingly difficult, because much more variability than previously recognized exists in the genotypic clusters G1-3 (=E. granulosus sensu stricto) and G6-10 (Echinococcus canadensis). To accommodate the heterogeneous criteria used for genotyping in the literature, we restrict ourselves to differentiate between E. granulosus sensu stricto (G1-3), Echinococcus equinus (G4), Echinococcus ortleppi (G5) and E. canadensis (G6-7, G8, G10). The genotype G1 is responsible for the great majority of human CE worldwide (88.48%), has the most cosmopolitan distribution and is often associated with transmission via sheep as intermediate hosts. The closely related genotypes G6 and G7 cause a significant number of human infections (11.04%). The genotype G6 was found to be responsible for 7.32% of infections worldwide. This strain is known from Africa and Asia, where it is transmitted mainly by camels (and goats), and South America, where it appears to be mainly transmitted by goats. The G7 genotype has been responsible for 3.72% of human cases of CE in eastern European countries, where the parasite is transmitted by pigs. Some of the samples (11) could not be identified with a single specific genotype belonging to E. canadensis (G6/10). Rare cases of human CE have been identified as having been caused by the G5, G8 and G10 genotypes. No cases of human infection with G4 have been described. Biological differences between the species and genotypes have potential to affect the transmission dynamics of the parasite, requiring modification of methods used in disease control initiatives. Recent investigations have revealed that the protective vaccine antigen (EG95), developed for the G1 genotype, is immunologically different in the G6 genotype. Further research will be required to determine whether the current EG95 vaccine would be effective against the G6 or G7 genotypes, or whether it will be necessary, and possible, to develop genotype-specific vaccines.International journal for parasitology 11/2013; · 3.39 Impact Factor
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ABSTRACT: Echinococcosis is a zoonosis caused by helminths of the genus Echinococcus. The infection, one of the 17 neglected tropical diseases listed by the World Health Organization, has a cosmopolitan distribution and can be transmitted through a variety of domestic, synanthropic, and sylvatic cycles. Wildlife has been increasingly regarded as a relevant source of infection to humans, as demonstrated by the fact that a significant proportion of human emerging infectious diseases have a wildlife origin. Based on available epidemiological and molecular evidence, of the nine Echinococcus species currently recognized as valid taxa, E. canadensis G8–G10, E. felidis, E. multilocularis, E. oligarthrus, E. shiquicus, and E. vogeli are primarily transmitted in the wild. E. canadensis G6–G7, E. equinus, E. granulosus s.s., and E. ortleppi are considered to be transmitted mainly through domestic cycles. We summarize here current knowledge on the global epidemiology, geographical distribution and genotype frequency of Echinococcus spp. in wild carnivorous species. Topics addressed include the significance of the wildlife/livestock/human interface, the sympatric occurrence of different Echinococcus species in a given epidemiological scenario, and the role of wildlife as natural reservoir of disease to human and domestic animal populations. We have also discussed the impact that human activity and intervention may cause in the transmission dynamics of echinococcosis, including the human population expansion an encroachment on shrinking natural habitats, the increasing urbanization of wildlife carnivorous species and the related establishment of synanthropic cycles of Echinococcus spp., the land use (e.g. deforestation and agricultural practices), and the unsupervised international trade and translocation of wildlife animals. Following the ‘One Health́ approach, we have also emphasised that successful veterinary public health interventions in the field of echinococcosis requires an holistic approach to integrate current knowledge on human medicine, veterinary medicine and environmental sciences.Veterinary Parasitology 01/2014; · 2.38 Impact Factor
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ABSTRACT: To investigate the presence of Echinococcus spp. in wild mammals of Kenya, 832 faecal samples from wild carnivores (lions, leopards, spotted hyenas, wild dogs and silver-backed jackals) were collected in six different conservation areas of Kenya (Meru, Nairobi, Tsavo West and Tsavo East National Parks, Samburu and Masai Mara National Reserves). Taeniid eggs were found in 120 samples (14.4%). In total, 1160 eggs were isolated and further analyzed using RFLP-PCR of the nad1 gene and sequencing. In 38 of these samples eggs of Echinococcus spp. were identified as either E. felidis (n=27) or E. granulosus sensu stricto (n=12); one sample contained eggs from both taxa. E. felidis was found in faeces from lions (n=20) and hyenas (n=5), E. granulosus in faeces from lions (n=8), leopards (n=1) and hyenas (n=3). The host species for two samples containing E. felidis could not be identified with certainty. As the majority of isolated eggs could not be analysed with the methods used (no amplification), we do not attempt to give estimates of faecal prevalences. Both taxa of Echinococcus were found in all conservation areas except Meru (only E. felidis) and Tsavo West (only E. granulosus). Host species identification for environmental faecal samples, based on field signs, was found to be unreliable. All samples with taeniid eggs were subjected to a confirmatory host species RLFP-PCR of the cytochrome B gene. 60% had been correctly identified in the field. Frequently, hyena faeces were mistaken for lion and vice versa, and none of the samples from jackals and wild dogs could be confirmed in the tested sub-sample. This is the first study on the distribution of Echinococcus spp. in Kenyan wildlife. The presence of E. felidis is confirmed for lions and newly reported for spotted hyenas. Lions and hyenas are newly recognized hosts for E. granulosus s.s., while the role of leopards remains uncertain. These data provide the basis for further studies on the lifecycles and the possible link between wild and domestic cycles of cystic echinococcosis in eastern Africa.Parasitology International 04/2014; · 2.30 Impact Factor