|a plasmodium causing malaria|
and others of the genus
Avian malaria is a
Avian malaria is most notably caused by Plasmodium relictum, a protist that infects birds in all parts of the world apart from Antarctica. There are several other species of Plasmodium that infect birds, such as Plasmodium anasum and Plasmodium gallinaceum, but these are of less importance except, in occasional cases, for the poultry industry. The disease is found worldwide, with important exceptions. Usually, it does not kill birds. However, in areas where avian malaria is newly introduced, such as the islands of Hawaiʻi, it can be devastating to birds that have lost evolutionary resistance over time.
Avian malaria is a
There exists much controversy on what corresponds as a species in avian malaria parasites. The Latin binomials nomenclature used to describe
Phylogeny of malaria parasites
To date, there is no specific phylogeny for avian malaria parasites and related haemosporidian parasites. However, given that malaria parasites can be found in reptiles, birds and mammals, it is possible to combine the data from these groups and a well resolved large phylogeny is available. For over a century, parasitologists classified malaria parasites based on morphological and life-history traits and new molecular data shows that these have variable phylogenetic signals. The current approach suggests that Plasmodium species infecting birds and squamate reptiles belong to one clade, and mammalian lineages belonging to a separate clade. In the case of Haemoproteus, this group has traditionally been classified based on the vector host, with one clade being transmitted to columbiform birds by hippoboscid flies and a second group transmitted by biting midges to other avian families. The molecular data supports this approach and suggests reclassifying the later group as Parahaemoproteous.
Phylogeography of avian malaria
Although a widespread disease, the culprit most commonly associated with the disease is
Contrary to the state of knowledge on parasite-avian interactions, parasite-vector relationships are relatively less explored. MalAvi does list several known vectors however as of 2015[update] this is not at all complete. Generally avian malaria organisms are vectored by Culex.
Virtually every individual of endemic species below 4,000 feet (1,200 m) in elevation has been eliminated by the disease. These mosquitoes are limited to lower elevations, below 5,000 feet (1,500 m), by cold temperatures that prevent larval development. However, they appear to be slowly gaining a foothold at higher elevations and their range may be expanding upwards. If so, most remaining Hawaiian land birds may become at risk to extinction.
Most of the Hawaiian Islands have a maximum elevation of less than 5,000 feet (1,500 m), so with the exception of the island of Hawaiʻi and East Maui, native birds may become extinct on every other island if the mosquito is able to occupy higher elevations.
Disease process and epidemiology
Plasmodium relictum reproduces in
The incidence of this disease has nearly tripled in the last 70 years. Notable among the species of birds most heavily affected were house sparrows, great tits, and Eurasian blackcaps. Prior to 1990, when global temperatures were cooler than now, less than 10 percent of house sparrows (Passer domesticus) were infected with malaria. In recent years, however, this figure has increased to nearly 30 percent. Likewise, since 1995, the percent of malaria-infected great tits has risen from 3 percent to 15 percent. In 1999, some 4 percent of blackcaps—a species once unaffected by avian malaria—were infected. For tawny owls in the UK, the incidence had risen from two or three percent to 60%.
Although new epidemics are expected to be driven by
The main way to control avian malaria is to control mosquito populations. Hunting and removing pigs helps, because wallows from feral pigs and hollowed out logs of the native hapu'u ferns provide dirty standing water where the mosquito breeds (USDI and USGS 2005). Around houses, reducing the number of potential water catchment containers helps reduce the mosquito breeding sites (SPREP Undated). However, in Hawaiʻi, attempts to control the mosquitoes by larval habitat reduction and larvicide use have not eliminated the threat.
It may also be possible to find birds that are resistant to malaria, collect eggs and raise young birds for re-introduction into areas where birds are not resistant, giving the species a head-start on spreading resistance. There is evidence for evolution of resistance to avian malaria in two endemic species, Oʻahu ʻamakihi and Hawaiʻi ʻamakihi. If other species can be preserved for long enough, they may evolve resistance as well. One tactic would be to reforest high-elevation areas on the island of Hawaiʻi, for example above the refuge of Hakalau on land managed by the Department of Hawaiʻian Homelands. This could give birds more time to adapt before climate change or mosquito evolution bring avian malaria to the last remaining bird populations.
- ^ PMID 12028770.
- JSTOR 1942550.
- PMID 24556563.
- OCLC 476614868.
- S2CID 198154866.
- ^ PMID 14965906.
- ISSN 1461-0248.
- ^ Engel, Joshua (8 April 2015). "Birds get malaria, too". Field Museum of Natural History. Retrieved 25 February 2022.
- S2CID 1447832.
- PMID 18248741.
- ISSN 1600-0587.
- ISSN 1755-098X.
- S2CID 7896992.
- ^ "How to Protect Hawaii's Rarest Birds From Avian Malaria". Audubon. 2015-11-16. Retrieved 2020-02-04.
- PMID 29753342.
- ^ Specter, Michael (15 July 2016). "How the DNA Revolution Is Changing Us". National Geographic Magazine.
- Valkiūnas, Gediminas; Iezhova, Tatjana A. (2018-05-29). "Keys to the avian malaria parasites". PMID 29843718. (GV ORCID: 0000-0003-0594-0280).
- "Plasmodium Infection in Poultry - Poultry". MSD Veterinary Manual. Retrieved 2022-01-07.
- "How Malaria Hurts Birds". National Audubon Society. 2015-06-16. Retrieved 2022-01-07.
- Cooperative Research Units (2018-10-18). "Avian Malaria". U.S. Geological Survey. Retrieved 2022-01-07.