Taxonomy and genetic diversity of zoonotic tapeworms in the species complex of Echinococcus granulosus sensu lato
Date
2018-07-06
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Abstract
Põistang-paelussi on liikide kompleks, mille vastsevorm põhjustab inimestel ja kariloomadel haigust nimega tsüstiline ehhinokokkoos. Selle tagajärjel hakkab vaheperemehes (tavaliselt rohusööja või inimene) maksas või kopsus arenema vedelikuga täidetud tsüst. Sümptomid on varieeruvad ning sõltuvad sellest, mis organis tsüst arenema hakkab, kus ta paikneb antud organis ning kui suureks ta kasvab. Teadaolevalt on inimeselt leitud kõige suurema tsüsti kaaluks olnud ca 3 kg. Inimese endani jõuab see parasiit reeglina läbi koera, kes on parasiidile lõpp-peremeheks. Haiguse ravimata jätmisel võib see lõppeda nii inimese kui looma jaoks surmaga.
Kuna antud parasiidi geneetiline mitmekesisus on väga lai siis on põistang-paelussi puhul valitsenud segadus liikide arvus. Mitmest liigist see koosneb? Erinevaid variante ehk genotüüpe on tuvastatud 9 (nummerdatud G1-G8, G10). Seejuures on nendel erinevatel geneetilistel variantidel erinevused elutsüklites (nt osad suudavad inimest nakatada, teised mitte), levikupiirkondades (ühed põhjapoolkeral, teised rohkem lõunas) ja ka haiguse sümptomite tõsiduses (G1 variandiga on haigus nt kiirema kulgemisega ja tõsisemate tagajärgedega). Nende mainitud erinevuste põhjal on leitud, et tegelikkuses koosneb põistang-paeluss hoopis mitmest liigist. Seejuures ei ole aga jõutud ühtsele arusaamisele, et kas G6-G8 ja G10 moodustavad ühe, kaks või kolm liiki. Siiani pole ka ära tõestatud, et G1-G3 peaksid üks liik olema. Kuna tegemist on tõsiste tagajärgedega haigusega, siis on oluline, et nii arstidel kui veterinaaridel oleks ühine arusaam sellest, millisest haigustekitajast juttu on. Leviku piiramiseks on oluline info ka potentsiaalsete levikumustrite tuvastamine.
Käesolevas doktoritöö tulemused näitasid, et siiani segadust põhjustanud G6-G8 ja G10 moodustavad kaks liiki – koduloomadel levinud G6/G7 on üks, ning metsloomade G8/G10 moodustavad teise liigi. Seejuures tõestasime esmakordselt ka G1/G3 liigilist kuuluvust. Samuti analüüsisime inimestelt kõige sagedamini leitud variantide levikumustreid ning leidsime, et loomakaubandusel on antud parasiidi levikule olnud suur mõju.
Echinococcus granulosus is a tapeworm species complex which causes cystic echinococcosis in humans and livestock animals. The larval form of this parasite is in the form of a fluid filled cyst, which typically develops in the liver or in the lungs of the intermediate host (herbivores, humans). Symptoms depend on the size and location of the cyst. So far the biggest cyst found in one patient has been about the size of 3 kg. Humans frequently get the infection through contact with dogs, who are the final hosts for this parasite. Left untreated, the disease can result in the death of the infected intermediate host. The genetic diversity of this parasite is considerably high and there has been no unanimous decision of how many species there actually are in this complex. The different variants or in other words – genotypes – that have been confirmed are numbered G1-G8 and G10. Over the years the evidence has been accumulating that there are a number of major differences between these genotypes and it has been suggested to regard a few genotypes as one species. However, no decision has been reached for G6-G10 – are they one, two or three species? No evidence has been presented to regard G1-G3 as one species either. However, for accurate communication between doctors and veterinarians, it is vital to reach a unanimous decision about the number of species and their names. Moreover, for potential control efforts to stop the spread of this disease, it is important to also collect data on the distribution patterns of this parasite. In the current thesis we show that the domestic genotypes (G6/G7) form one species, and the genotypes frequently associated with wildlife (G8/G10) form another. We also provided conclusive evidence to regard G1/G3 as one one species. What is more, we also looked at the distribution patterns and population structure of the genotypes most frequently associated with human infections, and found that animal transportation has had a major influence on the current population structure for this parasite species complex.
Echinococcus granulosus is a tapeworm species complex which causes cystic echinococcosis in humans and livestock animals. The larval form of this parasite is in the form of a fluid filled cyst, which typically develops in the liver or in the lungs of the intermediate host (herbivores, humans). Symptoms depend on the size and location of the cyst. So far the biggest cyst found in one patient has been about the size of 3 kg. Humans frequently get the infection through contact with dogs, who are the final hosts for this parasite. Left untreated, the disease can result in the death of the infected intermediate host. The genetic diversity of this parasite is considerably high and there has been no unanimous decision of how many species there actually are in this complex. The different variants or in other words – genotypes – that have been confirmed are numbered G1-G8 and G10. Over the years the evidence has been accumulating that there are a number of major differences between these genotypes and it has been suggested to regard a few genotypes as one species. However, no decision has been reached for G6-G10 – are they one, two or three species? No evidence has been presented to regard G1-G3 as one species either. However, for accurate communication between doctors and veterinarians, it is vital to reach a unanimous decision about the number of species and their names. Moreover, for potential control efforts to stop the spread of this disease, it is important to also collect data on the distribution patterns of this parasite. In the current thesis we show that the domestic genotypes (G6/G7) form one species, and the genotypes frequently associated with wildlife (G8/G10) form another. We also provided conclusive evidence to regard G1/G3 as one one species. What is more, we also looked at the distribution patterns and population structure of the genotypes most frequently associated with human infections, and found that animal transportation has had a major influence on the current population structure for this parasite species complex.
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Keywords
Cestoidea, Echinococcus granulosus, taxonomy, genetic diversity, phylogeography, echinococcosis