Haemoproteus


Haemoproteus is a genus of alveolates that are parasitic in birds, reptiles and amphibians. Its name is derived from Greek: Haima, "blood", and Proteus, a sea god who had the power of assuming different shapes. The name Haemoproteus was first used in the description of Haemoproteus columbae in the blood of the pigeon Columba livia by Kruse in 1890. This was also the first description of this genus. Two other genera — Halteridium and Simondia — are now considered to be synonyms of Haemoproteus.
The protozoa are intracellular parasites that infect the erythrocytes. They are transmitted by blood sucking insects including mosquitoes, biting midges, louse flies and tabanid flies. Infection with this genus is sometimes known as pseudomalaria because of the parasites' similarities with Plasmodium species.
Within the genus there are at least 173 species, 5 varieties and 1 subspecies. Of these over 140 occur in birds, 16 in reptiles and 3 in amphibia: 14 orders and 50 families of birds are represented. These include gamebirds, waterfowl, raptors, pigeons and doves, and perching birds or songbirds.

Taxonomy and systematics

Evolution

The earliest known fossil is of a Haemoproteus like organism was found in the abdominal cavity of a female biting midge trapped 100 million years ago in amber found in Myanmar.

Taxonomic history

The first description of this genus was in 1890 by Kruse who described Haemoproteus columbae in the blood of the pigeon
Columba livia. McCallum in 1897 showed that the process of exflagellation was part of sexual reproduction in these parasites and thought it probable that the same process occurred in Plasmodium. The first record of a haemoproteid parasite in a reptile was by Simond in 1901 who gave it the name Haemamoeba metchnikovi. The Sergent brothers in 1906 showed that the ectoparasitic fly Pseudolynchia canariensis was the vector of Haemoproteus columbae. Aragao in 1908 demonstrated the schizogonic stages of Haemoproteus columbae in the endothelial cells of the lungs of nestling pigeons infected by the bite of infected Pseudolynchia. It was generally believed that transmission of the parasites was by regurgitation during a blood meal until Adie showed that the parasites develop in the salivary glands in a fashion analogous to that of Plasmodium in mosquitoes.
The genus Halterium was created by the French parasitologist Alphonse Labbe for a species he observed with gametocytes in erythrocytes, with pigment granules, and halter-shaped when fully formed. This genus was soon subsumed into the genus Haemoproteus.
The genus Haemocystidium was created to give a name to the haemoproteid of a gecko belonging to the genus Hemidactylus in Sri Lanka by Castellani and Willey in 1904. A second species in this genus was described in 1909 by Johnston and Cleland who found pigmented gametocytes in the blood of the Australian tortoise Chelodina longicollis. These species were transferred to Haemoproteus in 1926 by Wenyon.
The genus was resurrected by Garnham in 1966 when he created a new generic name — Simondia — for the haemoproteids of chelonians. He followed the opinions of Wenyon, Hewitt and DeGiusti and suggested that all these parasites belonged to the one species — Simondia metchnikovi. He retained the name Haemocystidium for the haemoproteids of lizards.
A different genus of vectors was identified in 1957 by Fallis and Wood when they identified Haemoproreus nettionis in Culicoides downesi Wirth and Hubert in Ontario, Canada.
Levine and Campbell in 1971 moved all the species in Simondia and Haemocystidium into Haemoproteus an opinion that was followed by subsequent authors.
The genus Haemocystidium was resurrected again by Telford in 1996 when he described three new species of protozoa in geckos from Pakistan.
This genus like those of many protozoa may be further modified once additional DNA sequences are available. For instance, many DNA sequences have been identified for Haemoproteus in birds around the world in recent years, leading to new knowledge about the previously unknown diversity of this parasite in different regions

Subgenera

The species infecting avian hosts have been divided into two subgenera — Haemoproteus and Parahaemoproteus — a division proposed in 1965 by Bennett et al. These may be distinguished as follows:
Haemoproteus: Vectors are hippoboscid flies. Exflagellation does not occur below 20 degrees Celsius. Mature oocysts have diameters greater than 20 micrometres. The average length of the sporozoites is less than 10 micrometres. One end of the sporozoite is more pointed than the other. Although the majority are parasites of the Columbiformes, some species from this subgenus have also been reported in the Charadriiformes, Pelecaniformes and Suliformes.
Parahaemoproteus: Parasites of birds other than the Columbiformes. Vectors are biting midges. Exflagellation occurs below 20 degrees Celsius. Mature oocysts have diameters less than 20 micrometres. The average length of the sporozoites is greater than 10 micrometres. Both ends of the sporozoite are equally pointed.
While it was thought that Haemoproteus was limited to doves and related species, species in this genus have been isolated from frigatebirds.

Species list

The infective stage is the sporozoite which is present in the salivary glands of the vector. Once the vector bites a new host, the sporozoites enter the blood stream and invade endothelial cells of blood vessels within various tissues including those of the lung, liver and spleen. Within the endothelial cells, the sporozoites undergo asexual reproduction becoming schizonts. These in turn produce numerous merozoites which penetrate the erythrocytes and mature into either female gametocytes or male gametocytes. Gametocytes can then be ingested by another blood-sucking insect where they undergo sexual reproduction in the midgut of the insect to produce oocysts. The oocysts rupture and release numerous sporozoites that invade the salivary gland and serve as a focus of subsequent infection for another host once the insect takes its next blood meal.

Description

Only gametocytes are found in the blood. Asexual reproduction occurs in body organs especially the liver. The organisms occupy the majority of the cytoplasm, leaving the light magenta, finely granular, pink nucleus centrally located.
Taxonomy of this genus is difficult as there are few distinct morphological differences between the recognised species. Many of them were described under the 'one species-one host' hypothesis which is now thought to be potentially misleading. The morphological features most commonly used to describe a species include the number of pigment granules, the degree of encirclement of the host nucleus, the size of the parasite, the degree of host nucleus displacement and the degree of host cell enlargement. DNA studies should help to clarify this area but to date have rarely been undertaken.
The gametocytes have five basic forms
Pigment granules are refractile and yellow to brown in colour.

Pathology

Infections with most Haemoproteus species appear to produce subclinical infections.
Post-mortem findings include enlargement of the spleen, liver and kidneys. These organs may appear chocolate-brown due to hemozoin deposition. Cytologic imprints may reveal schizont-laden endothelial cells. Some species of Haemoproteus will also form large, cyst-like bodies within the skeletal muscles that resembling those seen with Sarcocystis species infections.
Pigeons infected with Haemoproteus columbae may develop enlarged gizzards; and anemia has been recorded.
Flocks of bobwhite quail may become infected with Haemoproteus lophortyx. Infected birds may suffer from reluctance to move, ruffled appearance, prostration and death. Other findings include parasitemia and anemia. Large megaloschizonts may be present in skeletal muscles, particularly those of the thighs and back. The average cumulative mortality for flocks experiencing outbreaks may be over 20%.
Experimental infection of turkeys with Haemoproteus meleagridis resulted in lameness, diarrhea, depression, emaciation, anorexia and occasionally anemia.
Muscovey ducks infected with Haemoproteus nettionis suffered lameness, dyspnea and sudden death.
In other avian species, anemia and anorexia have been reported occasionally. Importantly, new records of Haemoproteus are discovered constantly and should still be monitored for effects on host condition

Effect on vectors

H. columbae infects rock pigeons and is vectored by a hippoboscid fly. Both sexes of vector can transmit the parasite. Species of the Hippoboscoidea the superfamily to which Ps. canariensis belongs do not lay eggs. Instead the larvae hatch in utero, are fed internally by 'milk glands' and pass through three morphological stages before being deposited to pupate. The survival of female flies is significantly reduced when they were infected with the parasite. In contrast no effect is seen on male fly survival. Additionally the females produce fewer offspring when infected but the quality of the offspring does not seem to be affected.

Host records

Avian hosts

The concept of a "one host-one species" was originally used in the taxonomy of this genus as it appears that the parasites are at least moderately host specific. After this rule was found to be incorrect, it was suggested that the avian parasite species were limited to single avian families. From an inspection of the host records above it is clear that this is not the case.
The avian species known to be infected are listed below:
Order Accipitriformes
Family Accipitridae
Family Cathartidae
Order Anseriformes
Family Anatidae
Order Charadriiformes
Family Laridae
Order Ciconiiformes
Family Ciconiidae
Order Columbiformes
Family Columbidae
Order Coraciiformes
Family Alcedinidae
Family Brachypteraciidae
Family Bucerotidae
Family Meropidae
Order Falconiformes
Family Falconidae
Order Galliformes
Family Numididae
Family Odontophoridae
Family Phasianidae
Family Tetraonidae
Family Otidae
Order Passeriformes
Family Acrocephalidae
Family Corvidae
Family Dicruridae
Family Emberizidae
Family Estrildidae
Family Fringillidae
Family Hirundinidae
Family Icteridae
Family Laniidae
Family Meliphagidae
Family Mimidae
Family Motacillidae
Family Muscicapidae
Family Nectariniidae
Family Oriolidae
Family Paridae
Family Paradisaeidae
Family Parulidae
Family Passeridae
Family Ploceidae
Family Pycnonotidae
Family Sturnidae
Family Sylviidae
Family Thraupidae
Family Timaliidae
Family Turdidae
Family Vangidae
Family Zosteropidae
Order Pelecaniformes
Family Fregatidae
Family Threskiornithidae
Order Piciformes
Family Megalaimidae
Family Picidae
Order Phoenicopteriformes
Family Phoenicopteridae
Order Psittaciformes
Family Cacatuidae
Family Psittacidae
Order Strigiformes
Family Strigidae