Malaria

                               MALARIA

Course Objectives

•         Basic understanding of malaria                                   

–       Causative agents; life cycle

–       Epidemiology

–       Symptoms

–       Diagnosis

–       Treatment

–       Prevention

   

Introduction

§  Malaria is a life-threatening parasitic disease caused by Plasmodium (protozoan parasite)

§  Name means “bad air”

§  Vector borne disease

§  40% of the world’s population is at risk

§  90% of the deaths due to Malaria occur in Sub-Sahara Africa, mostly among young children.

§  Around 400-900 million people are affected  with at least 2.7 million deaths annually.

q Cases in Nepal

—  1963- 159 cases detected

—  2002- 12,750 cases detected

—  2006- 4,969 cases detected

Causative agents

•         Plasmodium  species: 

•         P falciparum

•         P vivax

•         P ovale

•         P malariae

Life cycle

•         In 2 different hosts:

–       Man: as an intermediate host

–       Mosquito: Definitive host

Life cycle in human

1, Human infection begins with the bite of

infected female Anopheles mosquito. Mosquito

during bite, sporozoites with saliva inject into

small blood vessels of man.  These motile

sporozoites are carried within half an hour  to

the liver by the blood stream.

Pre erythrocytic schizogony or stage

In the liver cells sporozoites under go a

stage of asexual reproduction forming

schizont which contains 2000 to 50,000

merozoites. Finally mature schizont

ruptures releasing 1000 of merozoites into

the blood stream.

Erythrocytic schizogony or stage

In the blood stream merozoites attach to the

receptors of (glycophorine) RBC and invade

them and develop into young trophozoite.

These feed on the HB and produces malaria

pigment; compound of haematin and ferric

acid as an end product of Hb break down.

The trophozoites multiply with division of

nucleus followed by division of cytoplasm to

become mature schizonts – ruptures- release

merozoites- infects new RBC.

Gametocytogenesis

After 2-3 erythrocytic cycles , some

merozoites  in RBC instead of developing

into trophozoites and schizonts , develop

into male and female gametocytes.

In the mosquito

-          Mosquito during bite ingest these gametocytes. In the mid gut of mosquito male fertilizes the female by fusion forming zygote-become mature and develop into motile ookinete. It penetrates gut wall of the stomach and-grows into oocyst, large no. of sporozoites are formed in the oocyst-when maturation occurs, it ruptures and liberate sporozoites in the body cavity that spread to all parts of the mosquito , particularly to the salivary gland of the mosquito. Sporozoites are infectious to man and gametocytes are infectious to mosquito

Transmission

•         Man is the only important reservoir

•         Vector is female Anopheles mosquito

- Rainfall:        thrive in tropical areas

–        Altitude:          rarely exist above 2000 meters

–        Terrain:           coastal areas and lowlands with lots of freshwater breeding sites

–        Transmission also possible through:

1. Blood transfusion
2. Contaminated needle
3. Organ transplant
4. Congenital

Susceptibility

•         Universal susceptibility

•         No absolute immunity

–        Partial immunity in areas of high endemicity