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Mosquitoes
1. Rumala Morel
Dept. of Parasitology
Peradeniya
Y2S2
Mosquitoes of Medical
Importance in Sri Lanka
Aedes
Anopheles
Culex
2. MEDICAL ENTOMOLOGY
Study of insects and other
arthropods of medical importance
Insects: Mosquitoes, Flies, Midges,
Lice, Bugs, Fleas
Other arthropods: Ticks and Mites
3. Objectives:
List the major mosquito borne diseases
that occur globally
List the mosquitoes of medical importance
in Sri Lanka indicating the diseases they
transmit
Outline the life cycle of a mosquito
Describe the breeding & biting habits of
the medically important mosquitoes in Sri
Lanka
Outline the strategies used for control of
these mosquito species in Sri Lanka
5. Role of mosquitoes in disease transmission
2500 yrs ago Susruta suggested
transmission of malaria by mosquitoes
but no definite proof until end of 19th
C
1859- James Emerson Tennent in
‘Ceylon: An account of the island’
….retiring punctually at sunset and
sleeping under mosquito ‘curtain’ is a
valuable prophylactic against fevers…
6. Medical importance of Mosquitoes
biting nuisance- pests/allergy
vectors of disease
transmit disease causing organisms
Mosquitoes as biological vectors
Essential part of the life cycle takes place in
the vector- multiplication or development
or both
Specific time period necessary
before vector can infect another host
7. Mosquitoes as vectors of disease:
some important discoveries
1878 Patrick Manson- filarial
parasites
1897 Ronald Ross- malaria
1900 Reed & team- yellow fever
1902 Graham- dengue
8. Aedes aegypti Dengue Dengue viruses
Chikungunya Chikungunya virus
A.albopictus Dirofilariasis Dirofilaria repens
Mosquito borne diseases in Sri Lanka
MOSQUITO DISEASE INFECTIVE ORGANISM
Anopheles culicifacies Malaria Plasmodium spp.
Culex quinquefasciatus Bancroftian Wucheraria bancrofti
filariasis
C. gelidus Japanese Jap Encephalitis virus
C. Tritaeniorynchus encephalitis
C.pseudovishnui
Yellow fever – globally impt. mosq.borne disease
Not found in SL
9. Biological characteristics influencing
disease transmission
only females suck blood (blood required for
egg maturation)
breeding habits: preferred water type
host preference – anthropophilic
- zoophilic
blood sucking behavior- daytime/night
indoor/outdoor
survival- 3-4 weeks (to allow development of
pathogen)
flight range- 0.5 - 1.5 km
11. SEX DETERMINATION - Antenna
Classification of mosquitoes -1. SEX
"plumose" (hairy) - male
"pilose" (not very hairy)
female
12. Palps (sensory organs just lateral to the proboscis)
Classification of mosquitoes – 2. GENERA
A female mosquito
with long palps = Anopheles
A female with
short palps =
Culicine
Anopheles mosquitoes
rest and bite with their
bottoms up @ 45 degree
angle to the skin
13. Life span
1 month
150-300
laid every 48-72 h
4 stages
1-3 weeks
2-3 days
2-3 days
Mosquito
Life Cycle
Water is
essential
for breeding
14. Eggs:
laid singly
with floats
Eggs:
in clusters
Larvae:
parallel to
surface
no siphon
tube
Larvae:
siphon tube +
Adult: rests @
45º angle to
surface
Adult: rests
parallel to
surface
15. Aedes rests parallel to surface
Anopheles culicfacies also
rests parallel to surface like culex
16. Anopheles species of importance in Sri Lanka
An. culicifacies- major vector of malaria
vectors of minor importance
An. subpictus
An. annularis
An. vagus
An. tesselatus
Major vectors in other countries
An. gambiae- vector of human malaria and
Bancroftian filariasis in Africa
17. Characteristics of importance for a malarial vector
density
longevity
biting habits- anthropophilic (man
biting)
- outdoor/indoor
night biting mosquitoes
Keys/charts used for species identification
Rests on walls – Indoor Residual Spraying
Effective control method
18. Anopheles culicifacies
Distribution: Sri Lanka, India, Myanmar
Pakistan, Middle East, Nepal, Thailand
Adult: small- medium
wings & female palps - banding
resting position culicine-like
Breeding: shallow, sunlit, clear fresh water
Eg. Edges of slow flowing streams/rivers;
rain water collections in ground pools and pits
19. Dry zone: endemic species
present throughout year but high
densities with rains (NE monsoon Oct-Jan)
Intermediate zone: seasonal breeding
Wet zone: not normally found but breeding
occur with failure of monsoons due to
pooling in river beds
Found up to 900 m height
Distribution in Sri Lanka
Anopheles culicifacies
20. Rain water collections in pits,
construction sites, hoof prints
in dry zone
Stream/river bed pools;
seepage pools at
margins of lakes,
reservoirs;
open irrigation canal
margins
27. Culex quinquefasciatus
Very common urban domestic mosquito throughout
South/SE Asia- vector of bancroftian filariasis
Small, brown, absence of markings
Breeding: eggs in rafts (75-100 eggs)
highly polluted (organic matter) stagnant water
eg. blocked drains, cess pits, waste water pits
Habits: night biter, outdoor/indoor
bites man, cats/dogs
Rests in shade eg. indoors in dark corners
clothes, under furniture etc.
28. Culex quinquefasciatus Biological vector
Lymphatic filariasis:
Microfilaria ingested with the blood meal develop into
Infective larvae L3 in 10-12 days and emerge from
proboscis during the bite
ONLY development NO multiplication
29. Breeding sites of Culex quinquefasciatus
Stagnant,
polluted water
(sewage)
35. Aedes spp.
Ae. aegypti Ae. albopictus
Small, delicate, black & white banding on legs.
wings clear
Vectors of-
Dengue fever, Chikungunya, Dirofilaria repens
Yellow fever (not in Sri Lanka)
Breeding: eggs laid singly (no floats)
damp surfaces that get submerged
rain water collections in containers
36. Vectors of
Dengue & Chickungunya
Aedes aegypti
Ae albopictus
Container breeders, clean water
artificial- tyres, tin cans, plastic waste
Indoors- flower vases etc.
Natural- cut bamboo stumps, leaf axils
37. SL: dengue endemic since 1989
Transovarian transmission of arboviruses
Aedes breeding sites
40. Vector of Brugian filariasis
& Dirorfilariasis
Water plants:
Pistia
Eichornia
Salvinia
Mansonia spp.
M uniformis
M annulifera
Brown, speckled wings (light/dark scales)
Breeding: aquatic plants
eggs laid in clusters on undersurface
leaves of water plants
Larvae/pupae attached to plant roots
41. Armigeres subalbatus
Very common dusk/night biter
Pest & vector of Dirofilaria repens
Breeding: polluted water
Dirofilariasis
Dirofilaria repens: common
parasite of dogs
transmitted
by Aedes,
Armigeres,
Mansonia
Causes subcutaneous
nodules in humans
43. Reduce vector density 1
Adult control – Malaria control
(1) Insecticide impregnated
bed nets – treat every 6/12
(2) Indoor Residual Spraying
44. Reduce vector density 2
Eliminate breeding sites
Destroy larvae
Aedes spp.
• Properly dispose of old tires, cans, bottles,
water-collecting rubbish, and other
unused/unwanted containers.
• Eliminate breeding in standing pools of water
Eg. air conditioners, refrigerators – add surface
oil layer
• Clean birdbaths, vases, plant pots, rain
barrels, kiddie pools etc. ONCE A WEEK
Since 1986, several outbreaks of malaria have occurred in the traditionally non-mal;rious areas. These were related to hydrological changes below dams causing pooling in the rocky and sandy river bed linked with water diversion and aggravated by droughts. In addition human migration between the downstream settlements and upper non malarious areas promoted parasite carriage.
Infection is associated with prolific breeding of the vector in blocked drains, sewage pits and polluted stagnant water collections that are common in the poorly planned urban environment. such sites also favour breeding of Armigeres mosquitoes.
the outdoor agricultural lifestyle and rural dwellings carry high risks of man-mosquito contact.
The global emergence of dengue fevers as an urban public health problem is associated with Aedes breeding. Modern lifestyles with widespread use of 'thowaway containers that end up in refuse are ideal breeding sites. 90% of Aedes breeding in in Sri Lanka occur in discarded receptacles, empty coconut combs and used tyres made use of for varying purposes.
