Mosquitoes vectors of malaria and their control

UNIVERSITY OF BUEA
DEPARTMENT OF MEDICAL LABORATORY
SCIENCES
TAKU NELSON ORU
Bsc Medical Laboratory Science
Email:nelsonoru11@gmail.com
1

MOSQUITOES VECTORS OF MALARIA AND
THEIR CONTROL
Mosquitoes as disease vectors plays a very important
role in the transmission of human diseases like ;
dengue, microfilaria and malaria.
2

SOMETHING TO PONDER
 What is the world’s deadliest animal?
3

ANSWER
Many of us view mosquitoes as more of an annoyance
than a threat, but the tiny insects are far and away the
deadliest animals on earth.
The World Health Organisation estimates that 725,000
people are killed each year by mosquito-born diseases.
A staggering 200 million people are at least temporarily
incapacitated by malaria alone, of which 600,000 die.
Dengue fever, yellow fever and encephalitis are also
deadly diseases carried by mosquitoes.
At least one influential individual is spreading the word
about the killer insects.
4

MOSQUITOES: INTRODUCTION
 There are about 3000 species of mosquito, of which
about 100 are vectors of human diseases
 Mosquitoes and ticks account for the majority of
transmissions of the most important vector-borne
diseases, although some close relatives of
mosquitoes also get involved, including sand flies
and black flies
5

MOSQUITOES: BIOLOGY
 Mosquitoes differ from the other biting Diptera in having a
long slender body, long legs and long needle-shaped
mouthparts
 The wings sometimes have discernible patterns of scales
 The adult insects measure between 2 mm and 12.5 mm in
length
 Some species bite in the morning or evening and at night
 Species may bite indoors or out of doors.
7

MOSQUITOES: ANATOMY
Anatomy of a Mosquito
The Animal Files.com
8

MOSQUITOES: LIFE-CYCLE
Mosquitoes undergo complete metamorphosis (egg larvapupa adult )
WHO, 2010
10

LIFE CYCLE CONT…
 Female mosquitoes usually lay about 30-300 eggs
at one oviposition.
 Larvae will emerge after 2-3 days in the tropics,
and 7-14 days in cooler temperature weather
 There are four active larval stages.
 All larvae require water to develop
11

LIFE CYCLE CONT
 Mosquito larvae feed on yeasts, bacteria, protozoa and
numerous other plants, microorganisms found in the
water.
 Some of them are surface-feeders (e.g. Anopheles),
while many others browse over the bottom.
 Larval development ranged from 5-7 days to 7-14 days
(in the tropics)
12

LIFE CYCLE CONT…
 All mosquito pupae are aquatic and coma shaped
 Pupae do not feed, but spend most of their time at the
water surface taking in air through respiratory trumpets.
When disturbed, they will swim up and down in a jerky
fashion.
13

MOSQUITOES: BEHAVIOR
 Female mosquitoes feed on animals and humans
 Attracted by the body odours, carbon dioxide and heat
emitted from the animal or person
 Some species prefer biting at certain hours, for example
at dusk and dawn or in the middle of the night
 Feeding usually takes place during the night but daytime
biting also occurs
 Some species prefer to feed in forests, some outside of
houses, others indoors.
15

MOSQUITO-BORNE DISEASE
Malaria specific species of mosquitoes are particular to the
protozoans
16

MALARIA VECTORS AND THEIR
PATHOGENS
Disease Pathogen Vector species
Malaria Plasmodium vivax Anopheles sp.
P. falciparum
P.malariae
P. ovale
p.knowlesi
17

 Anopheline eggs are laid singly
on the water surface, possess
floats
 All Aedes lay their eggs singly,
on the ground, at or above the
waterline, never possess floats
 Culex eggs are deposited in
rafts of 100 or more
 Anopheline – larvae never
have a siphon. Lie parallel to
water surface
 Culicinae – all larvae have a
short or long siphon. Subtend
an angle from the water
surface
 Anophelines rest in a position
where their head, thorax, and
abdomen are in a straight line,
usually at an angle of 40 to
90°, whereas the culicines rest
in a position almost parallel to
the surface.
Characteristics of anophelines and culicines. (From Pictorial Keys to Some Arthropods and Mammals of
Public Health Importance, U.S. Department of Health, Education, and Welfare, Public Health Services,
Washington, D.C., 1964.)
18

ANOPHELES: BIOLOGY
 About 380 species of Anopheles occur around the
world
 Some 60 species are sufficiently attracted to
humans to act as vectors of malaria.
19

ANOPHELES: BEHAVIOR
 Anopheles mosquitoes are active between sunset and
sunrise.
 Each species has specific peak biting hours, and there
are also variations in their preference for biting indoors or
outdoors.
 The anophelines that enter houses to feed often rest
indoors for a few hours after feeding.
 They may then leave for outdoor sheltered resting sites,
among them vegetation, rodent burrows, cracks and
crevices in trees or in the ground, caves and the
undersides of bridges.
20

BEHAVIUORS CONT…
 Alternatively, they may stay indoors for the whole period
needed to digest the blood-meal and produce eggs.
 Indoor resting is most common in dry or windy areas
where safe outdoor resting sites are scarce.
 Once the eggs are fully developed the gravid
mosquitoes leave their resting sites and try to find a
suitable breeding habitat.
 Many Anopheles species feed on both humans and
animals.
 They differ, however, in the degree to which they prefer
one over the other.
 Some species feed mostly on animals while others feed
almost entirely on humans.
 The latter species are the more dangerous as vectors of
malaria. 21

ANOPHELES: HEALTH IMPORTANT
 Important malaria vectors :
An. aconitus
An. balabacensis
An. dirus
An. donaldi
An. flavirostris
An. letifer
An. leucosphyrus
An. maculatus
An. minimus
An. nigerrimus
An. subpictus
An. sundaicus
22

INTEGRATED VECTOR CONTROL APPROACH
 No single method is likely to provide a solution in all situations.
The present trend is to adapt a IVC approach.
 Vector control approach combining two or more methods with
a view to obtain maximum results with minimum efforts.
 “Integrated vector control approach is the present trend for
vector control defined as utilization of all appropriate
technological and management techniques to bring out an
effective degree of vector suppression in a cost effective
manner and also to avoid the overuse of one of the methods”.
 Selection of methods is not possible without detailed field
information on the ecology, bionomics of vectors, role in
disease transmission.
23

VECTOR CONTROL
Vector control is any method to limit or eradicate the mammals, birds,
insects or other arthropods (here collectively
called "vectors") which transmit disease pathogens.This can be
achieved in various ways;
1.Habitat and environmental control:
Removing or reducing areas where vectors can easily bred can
linit their growth. For example;
 Stagnant water removal, destruction of old tires and cans
which serve as mosquito breeding environments.
Reducing the prevalence of open defecation or improving the
designs and maintenance of pit latrines.
24

CONTROL CONT…
2.Personal protection
- Personal protection methods, used by individuals or
small groups of people to protect themselves from biting
insects and the diseases they may carry, act by
preventing contact between the human body and the
insects
- Repellents
- Protective clothing
- Insecticide vaporizers
-Impregnated Mosquito nets
25

CHEMICAL CONTROL
Larvicides :Bacillus thuringiensis iserailensis (Bti)-
Endotoxin : 2.5% suspension, 1 lit/50 m2, once every 2
weeks.
Insecticides:- e.g Malathion, Permethrin, Methoprene,
Resmethrin
Rodenticides
Repellents: DEET, indalone, diethyl benzamide,
dimethyl phathalate.
26

CHEMICAL CONTROL
Larvicide Formulation Duration
Petroleum oil- Diesel oil and Larvicidal oil Suspension 1-2 weeks
Paris green Granules 2 weeks
Organophosphorus compounds
Abate
Malathion
Fenthion
Chlorpyrifos
Emulsifiable conc
Emulsifiable conc
Emulsifiable conc
EC, Suspension
2-11 weeks
1-3 weeks
1-2weeks
2-4 weeks
Insect growth regulators- Diflubenzuron,
Methoprene, Pyriproxyfen
Suspension/
Granules
4-8 weeks
Bacterial Larvicides-
Bacillus thuringiensis H-14
B. Sphaericus
EC/ Granules 1-2 weeks
2-8 weeks
27

 Highly toxic to insect larvae or pupae, interfering with
development into adults. Used in large scales in US
 Safe to human beings and environment.
1. Juvenile hormone analogues: prevent development of
larvae into pupa or pupae into adult. Ex. Methoprene
2. Chitin synthesis inhibitors: interfere with moulting
process, killing larvae when they moult. Act more
rapidly.
Ex. Diflubenzuron and Triflumoron.
28

BIOLOGICAL CONTROL
 Natural enemies into the environment-includes
Insects, Viruses, Bacteria, Protozoa, Fungi and
Fish.
 Only two of them have become widely employed.
They are Larvivorous fish and Biolarvicides.
29

1.Larvivorous fish
 Feed on mosquito larvae.
 Easy, practical, cheap; they have no food value.
 They should have the following characteristics
 Preference for mosquito larvae over other types of food
 Small size
 High reproduction rate
 Tolerance to pollution, temperature fluctuation &
transportation.
 Two species are widely used-
Gambusia - clean water, tolerate wide range of temperature,
pH water salinities.
Guppy- Polluted water, cannot survive <10 degree C.
30

 Useful in ornamental tanks, wells, Garden ponds, fountains,
swimming pools, large water collection.
 Approximately 5 fish per sq.m of water surface.
Advantages
a. Long term effective control measure.
b. Cost effective.
c. Environmentally safe.
d. Controls variety of mosquito species.
Disadvantages
a. Effective when large numbers eventually establish
themselves.
b. takes 1-2 months; not suitable - quick anti larval measures are
needed.
needed.
31

 It is applied at 0.5 gm/sq.m
 250gm of B. thuringiensis is mixed with 10 L of water to
make 2.5% suspension & sprayed at 1L over 50 sq.m
every 2 weeks.
Bacillus sphaericus
 It also produces toxin.
 It is more effective in polluted water - suitable for
treatment of breeding sites of Culex.
 500gm of B. sphaericus with 10 L of water to make 5%
suspension & it is sprayed at 1 L over 50 sq.m. every 3
weeks.
Others Biolarvicides-
Fungi- Coelomyces, Culicinomyces,
Nematodes – Romanomermis cluicivorax and R. iyengari.
32

 Methods such as
1. sterile male technique
2. Cytoplasmic incompatability
3. Chromosomal translocations
4. Sex distortion
5. Gene replacement
Limitations:
1. Lack of mating competitiveness released males.
2. Immigration of fertile females from regions close to the
release sites.
33

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