Geven ongevaarlijke broertjes geheimen prijs van gevaarlijke Lassavirus?
- JoëlleGoüy de Bellocq
Heeft u al gehoord van het Lassavirus? Waarschijnlijk niet. Nochtans raken in West-Afrika elk jaar honderdduizenden mensen besmet. Hoe? Door contact met besmette veeltepelmuizen of hun uitwerpselen. Voor de meeste mensen verloopt de ziekte als een eenvoudig griepje: ze weten vaak zelfs niet dat ze Lassa opliepen. Een kleine groep krijgt echter ernstige bloedingen en Ebola-achtige symptomen. Waarschijnlijk bezwijken zo’n vijfduizend mensen elk jaar aan deze ‘Lassakoorts’. Dit zijn echter ruwe schattingen: eigenlijk is nog weinig geweten over dit gevaarlijke virus.
Net omdat het virus zo gevaarlijk is, moet het bestudeerd worden onder strikte bioveiligheidsnormen: het is dus een hele uitdaging om Lassa te bestuderen. Om dit te omzeilen, pasten we een slimme truc toe in mijn masterthesis. Ik bestudeerde het Lassavirus niet direct, maar ging op onderzoek naar Oost-Afrikaanse virussen die niet gevaarlijk zijn voor de mens. Waarom is dat zo slim? Deze arenavirussen komen voor in dezelfde gastheermuis en zijn nauwverwant aan het Lassa arenavirus. Door de veiligere virussen te bestuderen, kunnen we op een eenvoudigere manier veel meer te weten komen over hun gevaarlijke broertje.
Zo muis, zo virus
Het is best merkwaardig: de veeltepelmuis komt in bijna heel Afrika ten zuiden van de Saharawoestijn voor, maar draagt verschillende arenavirussen in verschillende regio’s. Zo komt het Lassavirus bijvoorbeeld enkel voor in West-Afrika, terwijl een ander virus, het Morogorovirus, enkel in het oosten van Tanzania wordt aangetroffen. De onderzoeksgroep Evolutionaire Ecologie van de Universiteit Antwerpen, waar ik mijn thesis uitvoerde, toonde eerder mee aan dat er verschillende groepen of ‘genetische lijnen’ veeltepelmuizen zijn. Het zou dus kunnen dat elk arenavirus specifiek is voor een bepaalde genetische veeltepelmuislijn.
Om dit beter in kaart te brengen, nam ik in mijn masterthesis deze specificiteit van verschillende Tanzaniaanse arenavirussen nader onder de loep. Ik kon gebruik maken van nier- en bloedstalen verzameld door Tsjechische onderzoekers van het ‘Institute of Vertebrate Biology’ van de ‘Czech Academy of Sciences’ en Tanzaniaanse onderzoekers van de ‘Sokoine University of Agriculture’. Zelf reisde ik ook naar Tanzania om veeltepelmuizen te vangen voor extra stalen. Zo kon ik in een zeer groot deel van Tanzania gedetailleerd op zoek naar arenavirussen.
De genetische lijn in het noorden van Tanzania bleek enkel het Gairovirus te dragen, die in het oosten het Morogorovirus en die in het zuidwesten het Lunavirus. Mijn resultaten bevestigen dus dat elk virus enkel in een bepaalde veeltepelmuislijn voorkomt. Bovendien was ik de eerste die het Lunavirus aantrof in Tanzania. Het werd eerder enkel aangetroffen in buurland Zambia.
Dynamische virussen en muizen?
Waarom welk virus nu net in welke muizenlijn voorkomt, is op dit ogenblik nog erg onduidelijk. Ook het antwoord op vele andere vragen blijft voorlopig nog een mysterie. Zoals: waarom vond ik geen arenavirussen in centraal Tanzania? En waarom kwam het Morogorovirus minder voor dan het Gairovirus? Mogelijk zijn er kleine verschillen in virus- of gastheerdynamiek. Is het ene virus soms besmettelijker dan het andere? Of heeft het eerder te maken met de migratiepatronen van de muizen?
Zulke verschillen in dynamiek kunnen nu onderzocht worden. We kunnen dus een volgende stap zetten en uitzoeken welk ongevaarlijk arenavirus in Tanzania het best geschikt is als model voor het gevaarlijke Lassavirus. Op die manier vormt mijn masterthesis een belangrijke schakel in een beter begrip van het gevaarlijke Lassavirus. Zijn ongevaarlijke broertjes vormen immers mogelijk een belangrijke bron van informatie over hoe het gevaarlijke virus zich gedraagt. Dankzij mijn masterthesis hebben we een betere basis om het beste tweelingbroertje op te sporen.
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