PLASMODIUM SPECIES

                      Plasmodium

Plasmodium species (Haemoparasite protozoa

The geographical distribution of Plasmodium 

Phylum Apicomplexa, Subphylum. Order Haemosporida, Family Plasmodiidae, Genus Plasmodium and species P. falciparum, malariae, vivax, and ovale. 

Common species of Plasmodium affecting humans

·                     Plasmodium falciparum – cause malignant tertian or sub tertian

·                     Plasmodium ovale – cause ovale malaria, Benign tertian malaria

·                     Plasmodium vivax – cause vivax malaria benign tertian malaria, mild

·                     Plasmodium malariae – cause malariae quartan malaria

Geographical distribution

Malaria is wide spread disease throughout the tropics and occurs also in many subtropical countries and parts of temperature regions.

Malaria believed to be responsible for 10 -15% of death in children below 5 years of age (in Africa South of Sahara and may invade other age groups.

·        Plasmodium vivax has a cosmopolitan distribution it is a wide spread in tropics and subtropics

·        The species is well adapted to temperature conditions

·        It still occurs rarely as far north as Siberia far South Argentina and South Africa.

·        Plasmodium malariae – has a wide spread distribution in warm countries and common in many parts of Africa, South America, India and Malaysia.

·        Plasmodium ovale: Is a rarest of all species and appear to be confined mainly in tropical countries particularly West Africa.

·        Plasmodium falciparum: Has a cosmopolitan distribution but it is a common in tropics and subtropics

 Habitats: 

In man:The habitats of the parasites occur in two hosts.

In man thee parasites live in the red blood cells and liver cell (paranchymal cells) during asexual reproduction.

The age of red blood cells appear to affect its invasion by particular species of the

Parasites e.g. plasmodium vivax parasites the youngest erythrocyte and plasmodium malarial the    oldest while plasmodium falciparum infects red cells of any age.

The following are stages which are found in man.

·      Trophozoite – the growing from of the parasites in the blood of man it include the ring form and all stage onwards except the fully growth gametocytes and cells (erythrocytes).

·      Schizonts – a form, which is in process of dividing as asexually it is called “immature” when division has just begun and mature when division is complete and the parasites cells, is just about to rupture

·      Merozoites. The process occurs in the liver cells and red blood cells of man

This origin of the parasites is not definitely known.

They are probably derived from merozoites produced by schizogony in the blood stream.

·      Gametocytes:

After Schizonts of red blood cell develop results in the formation of merozoites this stage of the parasite known as male and female gametes.

·      Schizogony – A process of a sexual reproduction by which, the nucleus and the cytoplasm divide into many subsidiary parts.

In mosquito:

In mosquito the parasites is found in the gut or wall in early stage and when fully developed they are found in salivary glands of mosquito.

·         Gametes: the male or microgametes and the female gametes or microgametes before the  fertilization has taken place.

·         Zygote The fertilized macrogamete

·         O ⁰o⁰   kinete: A zygote capable of moving results on development/developed zygote.

·         Oocyst:An O O kinete which has settled down become rounded and covered with membranous cysts wall

·         Sporogony process or cycle of sexual reproduction by which result in the formation of sporozoites. This process occurs in the mosquito

Morphological features Plasmodium falciparum 

The diagnostic morphological features of the human plasmodia are seen in blood smears stained by Giemsa or Field stains.

• The earliest form after invasion of the red cell is ring of bluish cytoplasm with dot like nucleus of red chromatin.
• The infected red blood cells are of normal size
• The presence of more than one ring form in a cell is relatively common.
• Presence of double chromatin dots in an infected red cell
• The gametocyte is banana-shaped

 

              Plasmodium falciparum trophozoite two parasites infected one RBC   

  

Plasmodium falciparum schizonts

                                                                           

Plasmodium falciparum gametocyte which is banana-shaped

The mode of transmission & life cycle  of Plasmodium species 

                                                                                                                                           

• Mosquito bite (Female Anopheles mosquito)
• Blood transfusion
• Congenital
• Use of contaminated syringe as in drug  addicts

Having two stages in their life cycle.

Schizogony or intrinsic cycle (asexual) inside human host

·         When an infected female mosquito bites an individual it introduces sporozoites (which are contained in its saliva) into either general blood circulation or lymphatics.

·         Within 30 minutes the sporozoites enter the liver (parenchyma cells where they grow and multiply by schizogony (pre-erythrocyte cycle or schizogony) leading to the production of large Schizonts which contain many merozoites.

·        Following maturation of Schizonts ruptured liberate merozoites

·        These young parasites (merozoites) may re-enter or invade other cells in the case of plasmodium ovale, plasmodium vivax and plasmodium malariae (especially old cells).

·        But this does not occur within plasmodium falciparum so, the one which are released into the blood will invade red blood cells to start the erythrocyte cycle (schizogony).

The cycle in the liver (exo- erythrocytic) takes:

·        8 days with plasmodium vivax

·        5 days with plasmodium falciparum

·        9 days with plasmodium ovale

·        11 – 12 days with plasmodium malariae

When merozoites invades red blood cells and start to feed cells it is called Trophozoites.

·        The trophozoites will then grow and multiply by schizogony leading to the production of Schizonts in the red cells.

·        Following maturation the red cells rupture releasing the Schizoints which also rupture to liberate the merozoites which then re – invade other blood cells

·        This process will continue repeatedly and it is here where we feel the malaria paroxysm.

·        The red cells cycle take 48 hrs with plasmodium falciparum, plasmodium vivax, plasmodium ovale and 72 hrs with plasmodium malariae

·        By mechanisms, which not known the merozoite that invade cells instead of growing and multiplying, they transform into female and male gametocytes.

·        Therefore, when another mosquito bites man it sucks blood with gametocytes.

Sporogony or extrinsic cycle (sexual cycle) outside the man

• When mosquito feed on man who is infected with (malaria) or harbouring the gametocytes it is sucks blood with female and male gametocytes.
• As the gametocytes are taken with the blood to the gut of the mosquito the female gametocyte develops to female gametes while the male gametocytes undergo a process of exflagellation i.e. forming flagella like process around themselves (6- 8 in number) these are male gametocyte.
• They detach from the parent cells and each will then fertilize the female to form a zygote.
• In the course of growth, the zygote elongates to form a worm like creature capable of moving called O o kinete.
• This then will move forward to the gut wall penetrate it and come to lie on the surface to form an Oocyst.
• Following maturation, the O o cyst will contain many sporozoites.
• This will rupture to liberate sporozoites, which then be distributed into entire body cavity of the fly (haemacoele).
• The sporozoites, which reach the salivary glands, are the one, which are infective to man.

The diseases caused by Plasmodium 

Malaria: The word in Italia means bad air (mal and aria) and it also known as paludism from a Latin word palus. Malaria is probably the most important of the vector borne disease which has three stages.

Cold stage:

·         Characterized by vigour and headache

·         The patient feels cold and shivers the temperature is high.

Fever stage:

·         The temperature rises to its maximum and the headache is severe usually, there are pains of back and joint and often vomiting and diarrhoea.

Sweating stage:

·         In which patient perspires the temperature fall and the headache and other pains are relived until the next rigor.

·         With p-vivax and p ovale produces tertian cases of malaria with fever every 3rd days ie at 48 hours intervals.

·         Plasmodium malariae cause malaria with every fourth days ie 72 hours interval (Benign)

·         Plasmodium falciparum causes malignant tertian the fever

·         There is spleen enlargement nausea, diarrhoea and blockage of fine capillaries due to the clumping of red cells and sticking on the capillaries wall.

·         Such, blocked vessels and swell and finally rupture of the intercranial haemorrhage cause coma and perhaps death (cerebral malaria) in very young children.

 Prevention  

Prevention and control recommended that malaria control should base on an epidemiologist approach.

Human control: Avoiding mosquito bite by: -

·         Selecting healthy sites for houses on the top of hills, exposure to prevailing wind and away from known mosquito breading sites where ever possible.

·         Screening windows and doors with mosquito netting.

·         Using effective mosquito bed nets during the biting hour of local mosquito vectors.

·         The impregnation of nets with insecticides such as perimethrin increases the protection.

·         Wearing protective clothing such as long trouces long skirts sarongs and garments with long sleeves.

·         Using mosquito repellents such as oil of tronella dimethylpathalate mosquito repellent coils or smoke from fire or from burning pyrethrum pellets

Using drugs to:

·         Treating active infection especially in young children

·         Suppress the infection until they die out.

·         Prevent infection by giving drugs every week (chemophylaxis ant malarial).

Mosquito control.

Preventing the breeding sites of mosquito larvae by: -

·         Altering the habit to discourage breeding e.g. preserving or planting vegetation where the vector needs sunshine or cleaning vegetation where vectors need shade.

·         Flooding or flushing of breeding sites (places)

·         Draining to remove surface water filling in pond or pots holes drainage ditches.

·         Changing the salts contents of the water.

·         Regularly spraying breeding sites with oil or chemicals.

Destroying adult’s mosquitoes by:

·         Regular spraying of all houses with residual insecticide such DDT or Malathion as part of programme control and providing no resistance of the mosquitoes to the insecticides.

Health education in:

·         Schools and village and training primary health care workers how to teach malaria control measures.

 Laboratory diagnosis:

·         Examination of stained thick, blood film to detect the parasites and to examine white blood cells for pigment from peripheral.

·         Examination of stained thin blood film to identify the species and give an estimated the percentage of red cells infected.

·         Examination of Buffy coat and red cells immediately below it after centrifuging blood in a small narrow bore tube. This can help sometimes if parasites are few.

 Key points: 

Trophozoite

·         The growing from of the parasites in the blood of man it includes the ring form and all stage onwards except the fully growth gametocytes and cells (erythrocytes).

Gametes:

·         The male or microgametes and the female gametes or microgametes before the            fertilization has taken place.

The mode of transmission of Plasmodium falciparum

• Mosquito bite (Female Anopheles mosquito)
• Blood transfusion
• Congenital
• Use of contaminated syringe as in drug  addicts
• Human control: Avoiding mosquito bite by: - Selecting healthy sites for houses on the top of hills, exposure to prevailing wind and away from known mosquito breeding sites where ever possible.

Evaluation: 

·         Explain the geographical distribution of Plasmodium species

·         Describe the mode of transmission & life cycle of Plasmodium falciparum in man.

·         Explain the diseases caused by Plasmodium falciparum.

References

1. Brown .H.W. (1968). Basic clinical Parasitology (3rd ed). New York: Meredith
2. CDC (2009). DPDx, Laboratory Identification of Parasites of Public Health Concern.
3. Cook, G. (2000). Manson’s Tropical Diseases (22nd ed.). London: WB Saunders
4. Harwood, R.F., James, M.T., (1979). Entomology in Human and Animal Health (7th ed.).
5. Mike, S. (2004). Medical Entomology for students. London: Oxford University Press.
6. Monica, C. (1987). Medical Laboratory Manual for Tropical Countries. Volume 1
7. Monica, C. (1998). District Laboratory Practice in Tropical Countries. Part 1. Tropical
8. Monica, C. (2000). District Laboratory Practice in Tropical Countries. Part 2. Tropical