Important Consequences For Human Health Research Articles

Several strains of Echinococcus granulosus infect livestock and humans in Argentina

Mitochondrial cytochrome oxidase subunit 1 (CO1) sequencing, Southern blot of a repetitive DNA element and single strand conformation polymorphism of the 5′ non-transcribed region of the cytosolic malate dehydrogenase (MDH) gene were used to determine the extent and distribution of Echinococcus granulosus genetic variation in Argentina. Five distinct strains of E. granulosus were shown to exist in the country. The common sheep, Tasmanian sheep, cattle and camel strains were identified in humans. Unlike the situation found in other countries, where the common sheep strain is the major source of human contamination, the Tasmanian sheep and camel strains produced a significant number of human infections in some regions of Argentina. This is the first report of cattle strain in humans in South America. Goats could be the natural intermediate host of the camel strain, which was not identified in humans from other regions so far. More than one genotype was identified in the same geographic area. These findings may have important consequences for human health and the control of hydatid disease. Within-strain differences were also observed, showing the potential of variation of E. granulosus.

Further molecular discrimination of Spanish strains of Echinococcus granulosus

We have designed two polymerase chain reaction (PCR) primer sets (PEg9F1-PEg9R1 and PEg16F1-PEg16R1) and two PCR protocols (Eg9-PCR and Eg16-PCR) for discrimination of Echinococcus granulosus genotypes. The oligonucleotide sequences originate from two E. granulosus DNA multiplex-PCR amplification fragments, previously reported, that allows species-specific discrimination between Taenia saginata, Taenia solium, and E. granulosus. The Eg9-PCR, Eg16-PCR, and Eg9-PCR linked restriction fragment length polymorphism (RFLP) analysis was used to characterize 53 E. granulosus isolates from the central region of Spain, highly endemic for echinococcosis. The analysis resulted in: (i) the discrimination of E. granulosus from Echinococcus multilocularis; (ii) the characterisation and discrimination of discrete E. granulosus strains from Spain; and (iii) the identification of two distinct genotypes within E. granulosus Spanish pig isolates. To further characterize the genetic variants in pigs, fragments of the NADH dehydrogenase I (ND1) and the cytochrome c oxidase subunit I (CO1) genes were amplified from parasite DNA and sequenced. The results again revealed the presence of two distinct genotypes: the G1 (sheep–dog strain) and G7 (pig–dog strain) genotypes. This observation could have important consequences for human health in Spain. Furthermore, the Eg9-PCR, Eg16-PCR, and Eg9-PCR-RFLP protocols can be used as additional methods to discriminate various E. granulosus genotypes.

BIODIVERSITY AND THE DILUTION EFFECT IN DISEASE ECOLOGY

Many infectious diseases of humans are caused by pathogens that reside in nonhuman animal reservoirs and are transmitted to humans via the bite of an arthropod vector. Most vectors feed from a variety of host species that differ dramatically in their reservoir competence; that is, their probability of transmitting the infection from host to vector. We explore a conceptual model of what we termed the “dilution effect,” whereby the presence of vertebrate hosts with a low capacity to infect feeding vectors (incompetent reservoirs) dilute the effect of highly competent reservoirs, thus reducing disease risk. Using Lyme disease as an example, we demonstrate the presence and estimate the magnitude of the dilution effect for local sites in eastern New York State. We found that the prevalence of Lyme disease spirochetes, Borrelia burgdorferi, in field-collected Ixodes ticks (37.6% and 70.5% for nymphal and adult stages, respectively) was dramatically lower than expected (∼90% and >95% for nymphal and adult stages, respectively) if ticks fed predominantly on highly competent reservoirs, white-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus). We inferred the role of additional host species using an empirically based model that incorporated data on tick burdens per host, relative population densities of hosts, and reservoir competence of each host. Assuming an empirically realistic reservoir competence of 5% for non-mouse and non-chipmunk hosts, we determined that alternative hosts must provide 61% and 72% of larval and nymphal meals, respectively. Using computer simulations, we assembled simulated host communities that differed in species richness, evenness, and net interactions between alternative hosts and mice. We found that increasing species richness (but not evenness) reduced disease risk. Effects were most pronounced when the most competent disease reservoirs were community dominants and when alternative hosts had a net negative influence on the dominance of mice as a host for ticks. Our results highlight a critical role of biodiversity and host community ecology in the transmission of vector-borne zoonotic diseases that in turn has important consequences for human health.

Genetic variation and epidemiology of Echinococcus granulosus in Argentina.

Polymerase chain reaction-ribosomal ITS-1 DNA (rDNA) restriction fragment length polymorphism (PCR-RFLP) analysis and sequencing of the mitochondrial cytochrome c oxidase subunit 1 (CO1) and NADH dehydrogenase 1 (ND1) genes were used to characterize 33 Echinococcus granulosus isolates collected from different regions and hosts in Argentina, and to determine which genotypes occurred in humans with cystic hydatid disease. The results of the study demonstrated the presence of at least 4 distinct genotypes; the common sheep strain (G1) in sheep from Chubut Province and in humans from Río Negro Province, the Tasmanian sheep strain (G2) in sheep and 1 human from Tucumán Province, the pig strain (G7) in pigs from Santa Fe Province and the carnel strain (G6) in humans from Río Negro and Buenos Aires Provinces. The finding that pigs harboured the pig strain and the occurrence of the Tasmanian sheep strain has considerable implications for the implementation of hydatid control programmes due to the shorter maturation time of both strains in dogs compared with the common sheep strain. Furthermore, this is the first report of the presence of the G2 and G6 genotypes in humans which may also have important consequences for human health.

Industrial Genotoxicology Group (IGG): Aneuploidy, White House Hotel, London, UK, 16 May 1997.

Aneuploidy has important consequences for human health. There is a requirement to detect aneugens that may not be fully satisfied by the current test batter. New cytogenetic techniques look promising.