''Plasmodium fieldi'' is a parasite of the genus ''

Plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...

'' sub genus ''

'' found in Malaysia. This species is related to ''

Plasmodium ovale ''Plasmodium ovale'' is a species of parasitic protozoon that causes tertian malaria in humans. It is one of several species of ''Plasmodium'' parasites that infect humans, including '' Plasmodium falciparum'' and '' Plasmodium vivax'' which ar ...

'' and '' Plasmodium simiovale''. As in all ''Plasmodium'' species, ''P. fieldi'' has both

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

and

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...

hosts. The vertebrate hosts for this parasite are

primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and lorisids, and the Haplorhini, haplorhines, which include the Tarsiiformes, tarsiers and ...

Description

This species was first described by Eyles, Laing and Fong in 1962. The parasite was identified in a pig-tailed macaque (''

Macaca nemestrina The southern pig-tailed macaque (''Macaca nemestrina''), also known as the Sundaland pig-tailed macaque and Sunda pig-tailed macaque, is a medium-sized macaque that lives in southern Thailand, Malaysia, and Indonesia. It is known locally as berok ...

'') that Eyles purchased in peninsular

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

in mid-August 1960.Eyles D.E., Laing A.B.G. and Fong Y.L. (1962) ''Plasmodium fieldi'' ''sp. nov.'', a new species of malaria parasite from the pig-tailed macaque in Malaya. Ann. Trop. Med. Parasit. 56:242–247 It was named after the malariologist Dr. John W. Field. The asexual cycle is 48 hours in length Ring forms: These measure about 3 micrometres in diameter and double chromatin bodies may be present. Multiple infections of the

erythrocyte Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

are uncommon.

Trophozoite A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing ''Plasmodium falciparum'' and those of the ''Giardia'' group. (The complement of the trophozoi ...

s: The

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

is compact, staining a deep blue while the

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

stains deep red.

Pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic comp ...

is dark and made up of fine grains. Schüffner-type stippling also taking a deep red stain appears about half way through this stage. Older trophozoites are compact, rounded or oval and display very little amoeboidity. The

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic ...

may be diminished or lost. Aggregates of dark eosinophilic masses sometimes larger than the nuclei may be present. Some host cells are oval-shaped and may be slightly enlarged.

Schizont Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

s: Immature forms have dense blue-staining cytoplasm and relatively large deep red nuclei. The pigment is granular, well-distributed and generally black in colour. Heavy stippling is present. As schizogony proceeds, the eosinophilic masses approximate forming a deep red border around the developing schizont. At this stage the host cell may be appreciably enlarged and some may assume an oval shape. Mature schizonts produce 4 to 16 (mean 12) large

merozoites Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

. The golden-brown pigment forms a large mass in the center of the schizont. The host cell may become greatly distorted. This characteristic distortion appears to be distinctive for this parasite.

Gametocyte A gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called '' spermatocytes'', and female gametocytes are called '' oocytes''. Developme ...

s: Mature macrogametocytes have an off-centre, dark red nucleus. The deep blue cytoplasm has delicate, dark pigment granules scattered within it. The host cell, which may be slightly enlarged, has a red ring of eosinophilic stippling within it. Mature microgametocytes occupy the entire the host cell and have dark pink cytoplasm. The off-center nucleus stains red and has a deep red bar-like mass. Pigment granules are heavy and fairly evenly distributed in the cytoplasm. The host cells show a pronounced stippling and may have fimbriated edges. Liver stages: These have been studied 6–14 days post infection. The exoerythrocytic bodies are circular to elliptical in shape and measure 20 micrometres in diameter at day 6 and 40–60 micrometres at day 14. The cytoplasm stains pale blue. The nucleus is about 1 micrometre in diameter. There are no morphological features to distinguish them from any other ''Plasmodium'' species. The life cycle in the

mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning "gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "lit ...

has been studied in several species. Although the details differ somewhat between species the outline is broadly similar. The

oocyst Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organis ...

s have a maximum diameter between 30 and 100 micrometres (mean 60 micrometres). Sporozoites appear in the

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivar ...

s about day 14. Transmission to human volunteers has not been successful.

Vectors

Hosts

''P. fieldi'' infects the kra monkey ('' Macaca irus'' or '' Macaca fascicularis'' ), the rhesus monkey (''

Macaca mulatta The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally b ...

''), the pig-tailed macaque (''

''), the bonnet macaque ('' Macaca radiata'') and the baboon ('' Papio doguera'').

References

{{DEFAULTSORT:Plasmodium Fieldi fieldi Parasites of primates