**20. Reptile infecting species**

Unlike the mammalian and bird malaria those species (more than 90 currently known) that infect reptiles have been more difficult to classify.

In 1966 Garnham classified those with large schizonts as *Sauramoeba,* those with small schizont as *Carinamoeba* and the single then known species infecting snakes *(Plasmodium wenyoni)* as Ophidiella. He was aware of the arbitrariness of this system and that it might not prove to be biologically valid. This scheme was used as the basis for the currently accepted system.[52]

These species have since been divided in to 8 genera –*Asiamoeba, Carinamoeba, Fallisia Garnia*, *Lacertamoeba,* and *Paraplasmodium* and *Sauramoeba.* Three of these genera *(Asiamoeba, Lacertamoeba* and *Plaraplasmodium)* were created by Telford in 1988. Another species *(Billbraya australis)* described in 1990 by Paperna and landau and is the only known species in this genus. This species may turn out to be another subgenus of lizard infecting *Plasmodium.*

With the exception of *P. elongatum* the exoerythrocytic stage occur in the endothelial cells and those of the macrophage - lymphoid system. The exoerthrocytic stage of *P. elongatum* parasite the blood forming celss.

The various subgenera are first distinguished on the basis of the morphology of the mature gametocytes. Those of subgenus *Haemamoeba* are round oval while those of the subgenera *Giovannolaia, Hiffia* and *Novyella* are elongated. These latter genera are distinguished on the basis of the size of the schizont: *Giovannolaia* and *Huffia* have large schizonts while those of *Novyella* are small.[52]

Species in the *subgenus Bennettinia* have the following characteristics:

The type species is *Plasmodium juxtanucleare.* 

Species in the subgenus *Giovannolaia* have the following characteristics:

Biology of Malaria Parasites 23

• *P. ovale* is found mostly in Africa (especially West Africa) and the island of the western pacific. It is biologically and morphologically very similar of *P vivax*. however, differently from *P. vivax,* it can infect individuals who are negative for the Duffy blood group, which is the case for many residents of sub-Saharan Africa. This explains the

• *P. malaria,* found worldwide, is the only human malaria parasite species that has a quartan cycle (three-day cycle). (The three other species have a tertian, two-day cycle.) If untreated, *P. malaria* cause a long-lasting, chronic infection that in some cases can last a lifetime. In some chronically infected patients *P. malaria* can cause serious

• *P. knowlesi* is found throughout Southern Asia as a natural pathogen of long-tailed and pigtailed macaques. It has recently been shown to be a significant cause of zoonotic malaria in that region, particularly in Malaysia. *P. knowlesi* has a 24 –hour replication

Members of the genus *Plasmodium* are eukaryotic microbes. Therefore, the cell and molecular biology of *Plasmodium* will be similar to other eukaryotes. A unique feature of the malaria parasite is its intracellular lifestyle. Because of its intracellular location the parasite has an intimate relationship with its host cell which can be described at the cellular and molecular levels. In particular, the parasite must enter the host cell, and once inside, it modifies the host cell. The molecular and cellular biology of host-parasite interactions

Malaria parasites are members of the Apicomplexa. Apicomplexa are characterized by a set of organelles found in some stage of the parasite's life cycle. These organelles, collectively known as apical organelles because of their localization at one end of the parasite, are involved in interactions between the parasite and host. In particular, the apical organelles have been implicated in the process of host celll invasion. In the case of *Plasmodium,* three distinct invasive forms have been identified: sporozoite, merozoite, and ookinete (see *Plasmodium* Life Cycle). The following discussion focuses on the cellular biology of merozoites and erythrocyte invasion. Reference to other Apicomplexa and *Plasmodium*

Merozoites rapidly (approximately 20sec.) and specifically enter erythrocytes. This specificity is manifested both for erythrocytes as the preferred host cell type and for a particular host species, thus implying receptor – ligand interactions. Erythrocyte invasion is a complicated process which is only partially understood at the molecular and cellular

cycle and so can rapidly progress from an uncomplicated to a severe infection.

greater prevalence of *P. ovale* (rather than *P. vivax*) in most of Africa.

complications such as the nephritic syndrome.

**22. Cellular and molecular biology of** *Plasmodium* 

involved in these two processes will be discussed.

sporozoites will be made to illustrate common features.

2. Reorientation and erythrocyte deformation

levels.[53] Four distinct steps in the invasion process can be recognized:

**23. Host cell invasion** 

1. Initial merozoites binding

3. Junction formation 4. Parasite entry


The type species is *Plasmodium circumflexum.*

Species in the subgenus *Haeamoeba* have the following characteristics:


The type species is *Plasmodium relictum*

Species in the subgenus *Huffia* have the following characteristics:


The type species is *Plasmodium elongated*

The type of spices subgenus *Novyella* have the following characteristics:


The type species is *Plasmodium vaughni*

## **21. Malaria parasites**

Malaria parasites are micro-organisms that belong to the genus *Plasmodium.* There are more than 100 species of *Plasmodium,* which can infect many animal species such as reptiles birds, and various mammals. Four species of *Plasmodium* have long been recognized to infect humans in nature. In addition there is one species that naturally infect macaques which has recently been recognized to be a cause of zoonotic malaria in humans. (There are some additional species which can, exceptionally or under experimental conditions, infect humans.)


• Schizonts conyain plentiful cytoplasm, are larger than the host cell nucleus and

frequently displace it. They are found only in mature erythrocytes.

• Exoerythrocytic schizony occur in the mononuclear phagocyte system.

• Mature schizonts are larger than the host cell nucleus and commonly distplace it. • Gametocytes are large, round, oval or irregular in shape and are substantially larger

• Mature schizonts, while varying in shape and size, contain plentiful cytoplasm and are

• Mature schizonts are either smaller than or only slightly larger than the host nucleus

• Gametocytes are elongated. Sexual stage in this subgenus resemble those of

Malaria parasites are micro-organisms that belong to the genus *Plasmodium.* There are more than 100 species of *Plasmodium,* which can infect many animal species such as reptiles birds, and various mammals. Four species of *Plasmodium* have long been recognized to infect humans in nature. In addition there is one species that naturally infect macaques which has recently been recognized to be a cause of zoonotic malaria in humans. (There are some additional species which can, exceptionally or under experimental conditions, infect humans.) • *P. falciparum,* which is found worldwide in tropical and subtropical. It is estimated that every year approximately I million people are killed by *P. falciparum,* especially in Africa where this species predominates. *P. falciparum,* can cause severe malaria because it multiples rapidly in the blood, and can thus cause severe blood loss (anemia). In addition, the infected parasites can clog small blood vessels. When this occur in the

• *P. vivax,* which is found mostly in Asia, Latin America, and in some parts of Africa. Because of the population densities especially in Asia it is probably the most prevalent human malaria parasite. *P. vivax* (as well as *P. ovale*), has dormant liver stages ("hypnozoites") that can activate and invade the blood ("relapse") several months or

• Exoerythrocytic schizongony occur in the mononuclear phagocyte system[52]

Species in the subgenus *Haeamoeba* have the following characteristics:

Species in the subgenus *Huffia* have the following characteristics:

The type of spices subgenus *Novyella* have the following characteristics:

brain, cerebral malaria results, a complication that can be fatal.

years after the infecting mosquito bite.

commonly found in immature erythrocytes.

• Gametocytes are elongated

than the host nucleus.

• Gametocytes are elongated.

*Haemoproteus.*

**21. Malaria parasites** 

The type species is *Plasmodium relictum*

The type species is *Plasmodium elongated*

they contain scanty cytoplasm.

The type species is *Plasmodium vaughni*

The type species is *Plasmodium circumflexum.*

