Epidemiology of malaria

1. Epidemiology Of Malaria

2. 1. Agent Factors
A ) . Agents
B ) . Reservoir of infection
C ) . Period of communicability
2. Host Factors
3 . Environmental Factors

3. 1. AGENT FACTORS
A. Agent :- Plasmodium Parasite is the only causative agent which
has four distinct species :
1. Plasmodium vivax : Widest demographic distribution.
Contribute 40% of total incidence in India.
2 Plasmodium falciparum : Cause cerebral malaria.
Generally contribute 50% of total incidence
of malaria but recently it’s contribution
INCREASED to 65% after 2014 onwards.

4. Malaria parasite connecting to a red blood
cell

5. 3. Plasmodium malariae : Seen in Tumkur & Hassan in Karnataka.
Contribute < 1% of total incidence
of malaria.
4. Plasmodium ovale : Very rare parasite in man .
Mostly confined to tropical Africa and Vietnam.

6. B. Reservoir Of Infection : Exclusively Human.
Exception is chimpanzees in tropical Africa which carry Plasmodium
malariae.
Conditions to serve as a reservoir :
1. The person must harbour both the sexes of gametocytes in his
blood.
2. The gametocytes must be matured ; immature forms do not
undergo further development.
3. The gametocytes must be viable i.e. if the patient received an
antimicrobial drug , the gametocytes lose their viability or
infectivity to mosquitoes.
4. The gametocytes must be present in sufficient density to infect
mosquitoes. ( Min 12/ cubic mm of blood )

7. C . Period Of Communicability :
It is time period during which an infectious agent may be
transferred directly or indirectly from an infected person to
another person, from an infected animal to humans, or from an
infected person to animals.
Plasmodium vivax : 4-5 days
Plasmodium falciparum : 10-12 days
Relapse period may be found.

8. 2. HOST FACTORS
A ). Age : Affect people of all age groups.
Newborn infants are considerably resistant to Plasmodium
falciparum due to high foetal Hb concentration.
B ). Gender : Male > Female
C ). Race : AA Haemoglobin > AS Haemoglobin
Normal RBC > RBC with Duffy negative.
D ). Pregnancy : May cause premature labour and intrauterine death.
E ). Socioeconomic Status : More prevalent in people with low socioeconomic
status.

9. F ). Housing : People living in ill-ventilated and ill-lighted house are
more prone to malaria. Type of construction , nature of walls and
surrounding also matters.
G ). Population mobility : Labourers and nomadic tribes are more
prone to malaria.
H ). Occupation : Farmers >> Others.
I ). Human habits : Nomadism , sleeping in open , not using mosquito
also increase the chances of malaria.
J ). Immunity : People from non-endemic areas suffer much . Infants
born from immunized mothers are protected generally during first
3-5 months due to maternal IgG.

10. 3. ENVIRONMENTAL FACTORS
A ). Season : More incidence in July – November.
B ). Temperature : 20°C – 30°C favours the life cycle of malarial parasite.
C ). Humidity : Optimal relative humidity – 60% . If relative humidity is
≥ 60% , mosquito become more active and feed more.
D ). Rainfall : Generally rain increase the opportunity of breeding but
heavy rainfall may cause adverse affects. In Shri Lanka , severe
epidemic of malaria followed years of drought.
E ). Altitude : Above ≥ 2000-2500 mt , mosquito not found.
F ). Man-made Malaria : Burrowed pits , garden pools , irrigation channels
etc increase the occurance of incidence of malaria.

11. VECTORS OF MALARIA
1. Density : Anopheles culicifacies need high density to cause malaria.
An. fluviatilis need very low density to do so.
2. Life span : Vector mosquito needs 10-12 days to become infective
after feeding on infected person.
This principle is used in Malaria Eradication Programs by
decreasing the life span of mosquito to 10 days.
3. Choice of Host : An. culicifacies ; on human blood 2-80%.
An. fluviatilis – Highly anthrophilic species.

12. 1. Whole body forms a straight line with abdomen
held higher than head.
2. Scale on abdomen are absent.
3. Abdomen is blunt or sharp ended depending upon
species.

13. 4. Resting habits : Endophily and Exophily.
An. labranchiae An. sundaicus
5. Breeding habits : Moving water – An. fluviatilis
Brackish water – An. sundaicus
Wells , fountains , overhead tanks – An. stephensi
6. Time of biting : Nocturnal feeding feeding between dusk and dawn
by female Anopheles only.
Only Aedes mosquito feed at day.

15. 7. Vectorial capacity :combined effect of the density of the vector
population, its susceptibility to infection, life span and probability of
feeding on man. It is distinct from physiological capacity to transmit
infection.
8. Resistance to insecticides : DDT resistance
Chloroquine resistance
Resistance against antifolate drugs

16. Mode of Transmission ( MOT )
A ). Direct Transmission : By bite of infected female Anopheles
mosquito.
B ). Indirect Transmission : By blood or plasma transfusion from donor
infected by malarial parasites.
C ). Congenital Malaria : Seen in neonates born from infected mother.
Seen in Nigeria.

17. Incubation period
It is duration of time between which agent factors entered into host
and first time appearance of clinical signs.
Falciparum malaria : 9-14 days
Vivax malaria : 8-17 days
Ovale malaria : 16-18 days
Quartern malaria : 18-40 days

18. CLINCAL FEATURES
A ). Cold Stage
B ). Hot Stage
C ). Sweating Stage

20. A ). Cold Stage
 Lassitude , headache , nausea and chilly sensation followed by
rigors and vomiting.
 Temperature 39°C-41°C with weak pulse.
 Skin feels cold ; later it become hot.
 This stage last in ¼ hr - 1 hr.

21. B ). Hot Stage
 Headache with full pulse and rapid respiration.
 Patient feels burning hot and dryness.
 This stage last in 2-6 hrs

22. c ). Sweating Stage
 Fever downs with profuse sweating.
 This stage last in 2-4 hrs.
Order of severity :
P. Falciparum > P. vivax > P. malariae > P. ovale

23. DIAGNOSIS OF MALARIA
1. Microscopy : High sensitive and quantify the parasite load
A ). Thick Smear : To screen the parasites.
B ). Thin Smear : To detect the species of the parasite and their stage
2. Serological Test : Usually become positive ≥ 2 weeks after
primary infection by which time the infection
May be cured.

24. Thin and thick blood smear for microscopy of
malarial parasite.

25. Micrograph of a placenta from a stillbirth due to maternal
malaria. H&E stain. Red blood cells are anuclear ;
blue/black staining in bright red structures (red blood cells)
indicate foreign nuclei from the parasites.

26. Electron micrograph of a Plasmodium falciparum -
infected red blood cell (centre), illustrating
adhesion protein "knobs"

28. 3. Rapid Diagnostic Test ( RDT )
Detect the circulating parasitic antigen of
malaria.