Study of Plasmodium vivax

 

Study of Plasmodium vivax

 

Introduction

Plasmodium vivax is a protozoan parasite responsible for causing malaria, specifically benign tertian malaria. It is transmitted to humans through the bite of infected female Anopheles mosquitoes. The disease is characterized by recurrent fever, chills, anemia, and splenomegaly.

 

Morphology

Plasmodium vivax exhibits different morphological forms during its life cycle:

Sporozoites (Infective Stage): It is Crescent-shaped. Sporozoites are motile and present in the salivary glands of mosquitoes.

Trophozoites (Ring Stage): It is irregular and amoeboid in shape. Presence of Schüffner’s dots in infected RBCs.

Schizonts (Erythrocytic Stage): It is large, multinucleated form within RBCs. It Produces merozoites.

Merozoites: It is Small, round forms that invade new RBCs.

Gametocytes: It is Crescent or round shape. They are found in peripheral blood, responsible for mosquito infection.

Life Cycle

The life cycle of Plasmodium vivax involves two hosts: mosquitoes (definitive host) and humans (intermediate host).

Life Cycle in Mosquito (Definitive Host)

1. Ingestion of Gametocytes: Female Anopheles mosquito ingests gametocytes from an infected human during a blood meal.
2. Fertilization and Zygote Formation: Male and female gametocytes fuse in the mosquito gut to form a zygote.
3. Ookinete Formation: The zygote elongates into an ookinete, which penetrates the gut wall.
4. Oocyst Development: The ookinete develops into an oocyst that undergoes sporogony, producing sporozoites.
5. Sporozoite Release: Mature sporozoites migrate to the mosquito’s salivary glands and are transmitted to a human host during the next bite.

Life Cycle in Humans (Intermediate Host)

1. Sporozoite Inoculation: Infected mosquito injects sporozoites into human blood.
2. Liver Stage (Exoerythrocytic Cycle): Sporozoites invade liver cells, developing into schizonts, which release merozoites into the bloodstream.
3. Erythrocytic Cycle: Merozoites infect red blood cells (RBCs), undergoing multiple developmental stages (trophozoite, schizont, merozoites) leading to RBC rupture and malaria symptoms.
4. Gametocyte Formation: Some merozoites develop into gametocytes, which are taken up by mosquitoes, continuing the cycle.

Prevalence and Epidemiology

Plasmodium vivax is widespread in tropical and subtropical regions. It is highly prevalent in South America, Southeast Asia and the Indian subcontinent.

Transmission depends on:

1. Presence of Anopheles mosquito vectors.
2. Climatic conditions (temperature, humidity, rainfall).
3. Socioeconomic and hygiene factors.

 

Pathogenicity

It causes benign tertian malaria, characterized by:

1. Cyclic fever spikes every 48 hours.
2. Chills, sweating, and anemia due to RBC destruction.
3. Enlargement of the spleen and liver.
4. Possible relapse due to dormant liver-stage hypnozoites.

Prophylaxis (Prevention and Control)

1. Vector Control:

1. Insecticide-treated nets (ITNs) and indoor residual spraying (IRS).
2. Elimination of mosquito breeding sites.

2. Personal Protection:

1. Use of repellents and protective clothing.
2. Avoiding outdoor exposure during peak mosquito activity.

3. Chemoprophylaxis:

1.      Antimalarial drugs (chloroquine, primaquine) in endemic areas.

4. Early Diagnosis and Treatment:

1. Prompt detection using microscopic examination and rapid diagnostic tests (RDTs).
2. Treatment with chloroquine and primaquine to prevent relapse.

 

References:

1. World Health Organization (WHO) Malaria Reports.
2. CDC Malaria Factsheet.
3. Recent studies on Plasmodium epidemiology and treatment strategies