Environment & Ecology
Introduction
Natural transmission of malaria depends on the presence
of and relationship between the three basic epidemiological
factors: the host, the agent and the environment.
Variations in climatic
conditions have a profound effect on the life of a mosquito
and on the development of malaria parasites. Hence,
climate influences malaria transmission patterns and
variations in seasonal incidence. The most important
climatic factors are temperature , rainfall and humidity.
Climate
Climate restricts the range
of vector-borne diseases, while weather affects the
timing and intensity of outbreaks. Aspects of climate
change are important in determining how serious the
health impacts are likely to be. These include:
- The overall warming
trend
- The disproportionate
warming of nights and winters
- The increase in extreme
and severe weather events
Upsurge of vector and water-borne
diseases often occur during EL Nino events. Flooding
creates fresh breeding sites. For example, the Horn
of Africa deluged with flooding in late 1997, experienced
upsurges of cholera, malaria and rift valley fever.
Global warming and the
expected climatic instability that accompanies it can
have grave consequences for our health and well being.
Back to top
Temperature
Temperature has a profound
influence on the developmental cycle of the malaria
parasites. The body temperature of the mosquitoes is
directly related to the environmental temperature. Malaria
parasites cease to develop in the mosquito when the
temperature is below 16ºC. P. falciparum sporozoites
can only develop at temperatures above 18ºC. The best
conditions for the development of Plasmodia in the Anopheles
and the transmission of the infection are when the mean
temperature is within the range 20-30ºC.
Back to top
Relative Humidity
A high relative humidity
lengthens the life of the mosquito. The lifespan of
the mosquito is an important factor in the development
process of the malaria parasite in the vector. Hence,
high relative humidity allows the parasite to complete
the necessary life cycle so that it can transmit the
infection to several persons.
Rainfall
The association
of malaria with rainfall is due not only to greater
breeding activity of mosquitoes, but also to the rise
in relative humidity and higher probability of survival
of female Anopheles. It is not only the total amount
of rainfall that is important but also its weekly and
monthly distribution.
Back to top
|
