Leucocytozoon
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Leucocytozoon (or Leukocytozoon) is a
The species of this genus use either blackflies (
Life cycle
Parasites in the genus Leucocytozoon have a life cycle that involves both a bird host, and a
The newly released merozoites infect either
The gametocytes are taken up by a blood-sucking fly as it bites the bird host. Gametocytes then mature in the insect
Description
The nuclei of the schizonts is enclosed in a trilaminar membrane with peripherally arranged chromatin. The schizonts also contain numerous cytomers also with trilaminar membranes and containing multiple ribosomes. Repeated invagination of the cytomeres gives rise to the merozoites which also have a trilaminar membrane.
The merozoites have
Two gametocyte forms are recognised: an elongated (sail-like) form and a compact spherical form. These are usually 12–14 micrometres long. The large gametocytes tend to grossly distort the infected cells and make cell identification difficult. A pseudopigment known as volutin may be present.
Evolution
It has been suggested that this genus arose after the two others genera Plasmodium and Haemoproteus, the latter originating from the late Oligocene or early Eocene at about the same time as Piciformes and Coraciiformes.[2]
Taxonomy
The genus is divided into two subgenera—Akiba and Leucocytozoon—based on the vector species.
The only known member of the subgenus Akiba is Leucocytozoon (Akiba) caulleryi which uses members of the genus Culicoides as its vectors.
The remaining species in the genus use members of the genus Simulium as their vectors.
In 1977, Greiner and Kocan in an extensive examination of species in the order Falconiformes declared that the only valid species infecting this order was L. toddi.[3]
L. dubreuili is considered to be restricted to the family
L. ziemanni infects owls.[4]
Diagnostic criteria
Form gamonts in white blood cells and/or erythrocytes. Gametocytes cause marked enlargement and distortion of the infected cell producing a football-like appearance.
No
Merogony occurs in the parenchyma of liver, heart, kidney, or other organs.
Hemozoin deposits (pigment) are not formed—a useful distinguishing feature for Leucocytozoon from Haemoproteus and Plasmodium.
Oocysts develop rapidly in 3–5 days. The oocysts are small and nonexpanding, reaching 13 micrometres in diameter and typically have less than 100 short, thick sporozoites.
The vectors are Simulium or Culicoides species.
The vertebrate hosts are birds.
Type species: Leucocytozoon ziemanni
Pathology
The typical pathology of infection with these parasites includes
. Gross lesions also include pulmonary congestion and pericardial effusion.Megaloschizonts appear as grey-white nodules found in the heart, liver, lung or spleen. Microscopically there is ischemic necrosis and associated inflammation in the heart, brain, spleen and liver due to occlusion of blood vessels by megaloschizonts in endothelial cells. Ruptured schizonts may induce granulomatous reactions in the surrounding tissues.
Clinically the majority of birds affected with leucocytozoonosis exhibit no signs. Among those that do the signs include mild to severe signs of anorexia, ataxia, weakness, anemia, emaciation and difficulty breathing.
The excess mortality due to Leucocytozoon in adult birds seems to occur as a result of debilitation and increased susceptibility to secondary infection.
Epidemiology
L. simondi is suspected to be a major parasite of
Host range
Bird hosts
- L. anatis—ducks
- L. andrewsi—chicken (Gallus gallus domesticus)[5]
- L. anseris—geese
- L. artamidis—wood-swallows (Artamidae species)[6]
- L. atkinsoni—common jery (Neomixis tenella)[7]
- L. balmorali—shrikes (Malaconotidaespecies)
- L. bennetti—hook-billed vanga (Vanga curvirostris)
- L. berestneffi—yellow-billed magpie (Pica nuttalia)
- L. bishopi—parrotbills (Paradoxornithidaespecies)
- L. bonasae—ruffed grouse (Canachites canadensis), ptarmigan
- L. bouffardi—weaver birds (Ploceidae species)
- L. brimonti—bulbuls (Pycnonotus species)
- L. caprimulgi—nightjars (Caprimulgidaespecies)
- L. caulleryi Mathis and Leger 1909—chicken (Gallus gallus domesticus)
- L. coracinae—swifts (Campephagidae)[8]
- L. danilewskyi—owl (Strix occidentalis)
- L. deswardti—Sugarbirds (Promeropidaespecies)
- L. dubreuili—American robin (Turdus migratorius)
- L. dutoiti—finches (Fringillidaespecies)
- L. frascai—rufous-headed ground-roller (Atelornis crossleyi)[9]
- L. fringillinarum—finches (Passer domesticus biblicus)[10]
- L. gentili—house sparrow (Passer domesticus)
- L. greineri—common sunbird asity (Philepitta castanea)[11]
- L. grusi— sandhill crane (Antigone canadensis)[12]
- L. hamiltoni—Bukharan great tit (Parus bokharensis)[13]
- L. lairdi—blue vanga (Cyanolanius madagascarinus)[11]: 1475–9
- L. liothricis—Old World babblers (Timaliidaespecies)
- L. lovati—greater sage-grouse (Lagopus mutus)
- L. maccluri—Thailand thrush (Zoothera marginata)[14]
- L. macleani Sambon 1908—chickens (Gallus gallus domesticus)
- L. majoris—yellow wagtails (Motacilla flava)
- L. marchouxi—Mauritian pink pigeon (Columba mayeri),[15]doves
- L. nectariniae—sunbird (Nectarinia olivacea)
- L. neavei—guinea fowl
- L. pogoniuli—tinker barbets (Pogoniulus subsulphureus)[16]
- L. pycnonoti—bulbuls (Pycnonotidaespecies)
- L. roubaudi—estrildid finches (Estrildidae species)
- L. sabrazesi Mathis and Léger 1910—chicken (better source needed]
- L. schoutedeni Rodhain, Pons, Vandenbranden and Bequaert 1913—chicken (Gallus gallus domesticus)
- L. schufneri Prowazek 1912- chicken (Gallus gallus domesticus)
- L. shaartusicum—redstart (Phoenicurus phoenicurus)
- L. simondii—ring-necked ducks (Somateria mollissima)
- L. smithi—turkeys (Meleagrisspecies)
- L. sturni—starlings (Sturnidaespecies)
- L. tawaki—penguins (Spheniscidaespecies)
- L. timaliae—Old World babblers (Timaliidaespecies)
- L. toddi—Coopers hawk (Milvago chimango), grouse
- L. trachyphoni—barbet (Trachyphonus purpureus) [16]
- L. ziemanni—eagle owl (Strix occidentalis)
- L. zosteropis—white-eyes (Zosteropidaespecies)
Vectors
- L. bonasae—Simulium aureum, Simulium latipes
- L. caulleryi—Culicoides arakawae
- L. lovati—Prosimulium hirtipes, Simulium japonicum, Simulium uchidai[19]
- L. simondi—Cnephia ornithophilia, Simulium rugglesi
- L. smithi—Simulium nigritarse
- L. tawaki—Austrosimulium ungulatum
Notes
Like many protist species and genera this genus is subject to ongoing revision especially in the light of DNA based taxonomy. Described species may be subject to revision.
- L. anatis and L. anseris are considered to be synonyms of L. simondi.
- L. andrewsi and L. schoutedeni are considered to be synonyms.
- L. bonasae, L. jakamowi and L. mansoni are considered to be synonyms of L. lovati.
- L. brimonti is considered to be a synonym of L. fringillinarum.
- L. costai and L. numidae are considered to be synonyms of L. neavei.
- L. francolini, L. kerandeli, L. martini, L. mesnili, L. sabrazesi and L. schuffneri are considered to be synonyms of L. macleani.
- The species L. galli is open to some doubt.
- L. molpastis is considered to be a synonym of L. brimonti
- L. monardi is considered to be a synonym of L. gentili
- L. toddi seems likely to be a cryptic species complex.
- L. turtur and its subspecies L. turtur orientalis are considered a synonym of L. marchouxi
History
The first described observation of a Leucocytozoon parasite may have been by
References
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