Identify the Life Cycle of Malarial Parasite

Objective

Study of the life cycle of malarial parasite (Plasmodium).

 

Theory

What is Malaria? 

Malaria is a vector-borne parasitic infection caused by the Plasmodium parasites, namely P. vivax, P. falciparum, P. ovale, and P. malariae, through the bite of female Anopheles mosquitoes that serves as a vector for transmission. The severity of the disease may vary depending on the species and overall health of the host.  

 

How can it be spread?  

The primary source of transmission is through the bite of infected mosquitoes.  

Other common sources include,  

  • Blood transfusion (contaminated). 
  • Organ transplantation. 
  • Shared use of needles or syringes contaminated with blood. 
  • From the infected mother to the fetus during pregnancy. P. falciparum plays a major role in increasing the risk of complications, including maternal anemia, low birth weight, premature birth, and stillbirth. 

 

Species of mosquitoes mainly cause malaria

There are 156 species of plasmodium causing infections. Among them, four species are true parasites of humans. These mosquitoes lay their eggs in freshwater, which is highly active at dawn and dusk, as well as at night. 

Species  Distribution  Symptoms 
Plasmodium falciparum  It is the most dangerous species. It is found in Asia, South America, and Africa.  Dizziness, muscle ache, fatigue, abdominal pain, sore back, seizures, nausea, vomiting, fever, headache, etc
Plasmodium ovale  This is the rarest type. It is found in the West African region.   Headache, fever, muscle ache, fatigue, diaphoresis (sweating), cough, abdominal pain, diarrhoea. 
Plasmodium malariae  Not as widespread. It is found in the tropical and subtropical regions of Central and South America, Africa, and Southeast Asia.  Chill and high fever 
Plasmodium vivax  Widely distributed in India. Geographically widespread species of plasmodium cause malaria in human beings Diarrhoea, fatigue and fever.

 

 

Lifecycle of malarial parasite (Plasmodium

Two hosts play a major role in the life cycle of a malarial parasite.  

  • A female Anopheles mosquito 
  • Human host  

                                       Fig I. Life cycle of malarial parasite - Plasmodium 

 

Transmission and initial stage (Ref. in Fig I. step 1 & step 2) 

  • The transmission starts from sharing the sporozoite into the human bloodstream to moving into the liver cells for multiplication.  
  • The multiplication occurs over 7 to 14 days (about two weeks). During this period, the host remains asymptomatic. 

 

Formation of merozoites (Ref. in Fig I. step 3 & step 4) 

It matures as merozoite in the liver and RBC (red blood cells) by asexual multiplication called schizogony.  

  • Liver multiplication is known as liver schizogony (1st and 2nd multiplication phase). 
  • RBC multiplication is known as erythrocytic schizogony (3rd multiplication phase). 

 

Liver Schizogony  

  • It has two distinct types, namely, pre- and exo-erythrocytic schizogony.  
  • In pre-erythrocytic, the sporozoites become large, spherical-shaped schizonts, and the nucleus multiplies asexually to form thousands of merozoites. During this stage, the blood remains sterile.  
  • In exo-erythrocytic, the merozoites enter fresh liver cells and grow as schizonts to produce new merozoites, known as metacryptozoites. 

 

Erythrocytic schizogony 

  • The 3rd phase of asexual multiplication occurs in the erythrocytes (RBC).  
  • The cycle starts after the transmission of metacryptozoites (new merozoites). 
  • In erythrocytic, schizogony undergoes several stages to produce merozoites in RBC every 48 hours after ingestion. 8 hours after ingestion.  

 

Multiplication and formation of gametocytes (Ref. in Fig I. step 5) 

  • Merozoites invade red blood cells after multiplication, potentially causing cell bursts and release along with the toxins, maturing into sexual gametocytes (male and female) in the bloodstream.   
  • The multiplication cycle initiates the symptoms of the onset of fever. 

 

Gamete formation and maturation (Ref. in Fig I. step 6, step 7 & step 8) 

  • The mature gametophytes are transmitted to the mosquito through a bite and mature into a sex cell called gametes.  
  • The gametes were sexually reproduced, and the fertilized female gametes developed as actively moving ookinetes and passed through to the midgut wall to produce oocysts on the exterior surface.  

 

Sporozoite formation and transmission (Ref. in Fig I. step 9 & step 10) 

  • The active sporozoite multiplication occurs in the oocyst. 
  • The sporozoites then migrate to the mosquito's salivary gland by rupturing the oocyst.  
  • Again, the sporozoites are transmitted to the healthy host through the infected mosquito's bite.  

 

Symptoms  

  • Fever is the initial symptom after the multiplication of merozoites in the RBC.  
  • Additional symptoms include diarrhoea, dizziness, abdominal pain, fatigue, muscle aches, and sore back.  
  • Malaria also shows flu-like symptoms such as chest pain, runny nose, and cough. 
  • The severe illnesses of anemia, jaundice, paralysis, convulsions, and loss of consciousness can be fatal.  

 

Diagnosis 

  • Blood Smear Test (Microscopy): The most common method uses special dyes (Giemsa stain) to examine the presence of malarial species in blood. 
  • Complete blood count: To detect anemia and estimate the platelet count. 
  • Rapid Diagnostic Tests (RDTs): To detect specific malarial antigens in the blood, particularly in remote areas, due to the unavailability of the microscope.  
  • Molecular Diagnosis: PCR (polymerase chain reaction) is used to identify parasite nucleic acids in blood. 
  • Serology: Indirect immunofluorescence assay (IFA) or ELISA (enzyme-linked immunosorbent assay) determines antibodies against malarial parasites. 
  • Drug Resistance Tests: Testing must be performed to identify the susceptibility of antimalarial compounds in the parasite. 

 

Treatment 

  • Antimalarial drugs play a major role in the treatment of malarial infections. Examples include artemisinin-based Combination Therapies (ACTs) and Chloroquine.  

 

Prevention 

  • Wear long jackets to prevent mosquito bites. 
  • Minimize outdoor activity during dusk and dawn when mosquito activity is particularly high. 
  • Using insect repellent with DEET (diethyltoluamide) on the skin may be useful. Always consult a doctor before using it.  
  • Keep your surroundings hygienic and clean. 
  • Avoid storing or accumulating water in the surroundings to prevent mosquitoes from multiplying.  

 

Learning Outcomes   

The student understands and learns about:

  • Malaria and different types of mosquitos are responsible for causing malarial infection.  
  • The life cycle and different stages of Plasmodium
  • The symptoms and the preventive measures of the disease.