02.02.2005
Uccelli resistenti alla malaria
Gli amakihi hanno sviluppato una resistenza genetica
 
Gli uccelli nativi delle isole Hawaii muoiono di malaria sin da quando le zanzare portatrici della malattia sono giunte sulle isole, all'inizio del secolo scorso. Ma per una specie particolare, gli amakihi hawaiiani, il discorso è diverso.
Bethany Woodworth del Pacific Island Ecosystems Research Center e colleghi hanno scoperto che il numero di amakihi nelle zone infestate dalla malaria è addirittura cresciuto nel corso dell'ultimo decennio, anche se quasi l'80 per cento degli uccelli risulta infetto (il maggior tasso d'infezione documentato nelle isole Hawaii).
In un articolo pubblicato sulla rivista "Proceedings of the National Academy of Sciences", i ricercatori scrivono di aver scoperto un numero maggiore di amakihi che vivono nelle foreste a basse altitudini, ricche di zanzare, rispetto a quelle ad altitudini elevate, relativamente libere dalla malattia. Gli scienziati ipotizzano che gli amakihi possano aver sviluppato una resistenza genetica alla malaria aviaria, e stanno progettando alcuni test per verificare questa teoria. Nonostante diversi studi precedenti avessero concluso che nelle zone in cui erano presenti le zanzare gli uccelli selvatici hawaiiani erano destinati all'estinzione, il fatto che gli amakihi convivano con queste zanzare indica che è all'opera una sorta di co-evoluzione. Secondo gli autori, i risultati dello studio potrebbero contribuire all'espansione delle politiche di conservazione in modo da includere anche le foreste a basse altitudini.

Bethany L. Woodworth, et al., "Host population persistence in the face of introduced vector-borne diseases: Hawaii amakihi and avian malaria". Proceedings of the National Academy of Sciences (2005). 


ECOLOGY
Host population persistence in the face of introduced vector-borne diseases: Hawaii amakihi and avian malaria
Bethany L. Woodworth *, , Carter T. Atkinson *, Dennis A. LaPointe *, Patrick J. Hart *, , Caleb S. Spiegel *,  , Erik J. Tweed *, , Carlene Henneman *,  ¶, Jaymi LeBrun *,  ||, Tami Denette *,  **, Rachel DeMots *,  , Kelly L. Kozar *, , Dennis Triglia *, , Dan Lease *,  , Aaron Gregor *,  , Tom Smith *,   and David Duffy

*Pacific Island Ecosystems Research Center, U. S. Geological Survey, Kilauea Field Station, P.O. Box 44, Hawaii National Park, HI 96718; and Pacific Cooperative Studies Unit, Department of Botany, University of Hawaii at Mnoa, 3190 Maile Way, St. John 410, Honolulu, HI 96822-2279

Communicated by Peter M. Vitousek, Stanford University, Stanford, CA, December 17, 2004 (received for review June 1, 2004)
 

The past quarter century has seen an unprecedented increase in the number of new and emerging infectious diseases throughout the world, with serious implications for human and wildlife populations. We examined host persistence in the face of introduced vector-borne diseases in Hawaii, where introduced avian malaria and introduced vectors have had a negative impact on most populations of Hawaiian forest birds for nearly a century. We studied birds, parasites, and vectors in nine study areas from 0 to 1,800 m on Mauna Loa Volcano, Hawaii from January to October, 2002. Contrary to predictions of prior work, we found that Hawaii amakihi (Hemignathus virens), a native species susceptible to malaria, comprised from 24.5% to 51.9% of the avian community at three low-elevation forests (55–270 m). Amakihi were more abundant at low elevations than at disease-free high elevations, and were resident and breeding there. Infection rates were 24–40% by microscopy and 55–83% by serology, with most infected individuals experiencing low-intensity, chronic infections. Mosquito trapping and diagnostics provided strong evidence for year-round local transmission. Moreover, we present evidence that Hawaii amakihi have increased in low elevation habitats on southeastern Hawaii Island over the past decade. The recent emergent phenomenon of recovering amakihi populations at low elevations, despite extremely high prevalence of avian malaria, suggests that ecological or evolutionary processes acting on hosts or parasites have allowed this species to recolonize low-elevation habitats. A better understanding of the mechanisms allowing coexistence of hosts and parasites may ultimately lead to tools for mitigating disease impacts on wildlife and human populations.
 

Hemignathus virens | host–parasite coevolution | Plasmodium relictum | Culex quinquefasciatus
 
 

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Abbreviations: ASL, above sea level; BRY, Bryson's Cinder Cone; MAL, Malama Ki Forest Reserve; NAN, Nanawale Forest Reserve; HY, hatch year; VCP, variable-circular plot.
 Present address: U.S. Geological Survey Forest and Rangeland Ecosystem Science Center, 3200 Southwest Jefferson Way, Corvallis, OR 97331.

¶ Present address: Minnesota Cooperative Fish and Wildlife Research Unit, University of Minnesota, 200 Hodson Hall, 1980 Folwell Avenue, St. Paul, MN 55108-6124.

|| Present address: 1260 Bay Shore Road, Brussels, WI 54204.

** Present address: Spring Hill Farm, 135 Princeton Avenue, Hopewell, NJ 08525.

 Present address: Biology Department, 414 East Clark Street, University of South Dakota, Vermillion, SD 57069.

 Present address: P.O. Box 1056, Volcano, HI 96785.

 Present address: 1 Elmwood Drive, Rutland, VT 05701.

 To whom correspondence should be addressed. E-mail: bethany_woodworth@usgs.gov.

© 2005 by The National Academy of Sciences of the USA