Plasmodium hermani

Plasmodium hermani is a parasite of the genus Plasmodium subgenus Huffia.

Like all Plasmodium species P. hermani has both vertebrate and insect hosts. The vertebrate hosts for this parasite are birds.

Description

This species was first described in 1975 by Telford and Forrester in a wild turkey^[1]

The presence and degree of pigmentation vary with maturity of the host cell. Host cell nuclei may be displaced, but are not distorted, except slightly by pressure from the parasite. The asexual stages parasitize all cells in the erythrocyte series. In heavy infections the parasites occur predominantly in erythroblasts and their precursors.

Schizonts are rounded with 6–14 nuclei arranged peripherally as a rosette. Infected cells are often rounded and enlarged.

Gametocytes are elongate and slender with irregular margins and are found exclusively in erythrocytes. The pigment is dispersed in black granules throughout the cytoplasm. The host cells may be somewhat distorted in shape by lateral hypertrophy.

Differential diagnosis

Plasmodium hermani can be distinguished from Plasmodium durae by

• low level (< 6%) parasitemia
• nonlethal in turkey poults
• absence of phanerozoites in capillary endothelium of the brain and viscera
• inability to infect chicks (Gallus domesticus)

Mature gametocytes of P. durae also exhibits the following characteristics which are not found those of P. hermani

• tend to lie obliquely within the host cell
• displace the nucleus to one pole of the cell
• possess one or more clumps of clear pigment granules

Plasmodium hermani resembles Plasmodium elongatum in

• schizogony in all types of erythrocyte precursors
• concentration of schizonts in heavy infections in bone marrow and spleen
• gametocyte morphology
• gametocytes occurring in erythrocytes only

It can be distinguished from Plasmodium elongatum by

• its lack of infectivity to passeriform and anseriform hosts
• by the strong immune response which develops in infected birds

Geographical occurrence

This species is found in Florida, USA.

Vectors

• Culex nigripalpus^[2]
• Culex restuans
• Culex salinarius^[3]
• Wyeomyia vanduzeei

Note: Cx. nigripalpus appears to be the main natural vector.

Clinical features and host pathology

This species infects knots (Calidris canutus), bobwhites (Colinus virginianus) and turkeys (Meleagris gallopavo).

Infection of turkeys causes anaemia, splenomegaly and decreased growth but is not normally fatal.

References