9 Mosquitoes

1. Arthropod vector Mosquitoes 1

2. Lecture outline Mosquitoes as disease vectors-its role as important human disease vector for dengue, microfilaria and malaria 2

3. Interesting facts Alexander the Great, conqueror of many nations, was vanquished by the bite of a tiny mosquito bearing malaria parasites The Black Death, decimator of Europe, killer of tens of millions worldwide is the work of a tiny flea vectoring the bacilli that cause bubonic plague from rats to people. 3

4. Something to ponder What is the world’s deadliest animal? 4

5. 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

6. Mosquitoes: Classification There are 442 species of mosquitoes in Malaysia, compared to 553 species (Indonesia), 416 species (Thailand) and 310 species (Philippines) 6

7. 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; others feed during the day Species may bite indoors or out of doors. 7

8. Mosquitoes: Anatomy Anatomy of a Mosquito The Animal Files.com 8

9. Mosquitoes: Male and Female 9

10. Mosquitoes: Larva Anatomy of a Mosquito Larva The Animal Files.com 10

11. Mosquitoes: life-cycle Mosquitoes undergo complete metamorphosis (egg  larva  pupa  adult ) WHO, 2010 11

12. 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 12

13. 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 tropical areas) 13

14. 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. 14

15. 15

16. Mosquitoes: behaviour 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. 16

17. Mosquito-borne diseases Mosquito-borne diseases are divided into three groups (according to the pathogens): - Protozoa diseases (e.g. Malaria). - Viral diseases (e.g. dengue, Japanese encephalitis). - Nematode diseases (e.g. filariasis ). 17

18. Mosquito-borne diseases and their vectors (virus disease) Disease Pathogen Vector species Virus JE JE virus Culex tritaeniorhynchus Culex fuscocephala Culex gelidus Culex vishui Culex pseudovishui Dengue Dengue Aedes aegypti Dengue virus Aedes albopictus hemorrhagic 18

19. Mosquito-borne diseases and their vectors (protozoa and nematode disease) Disease Pathogen Vector species Malaria Plasmodium vivax Anopheles sp. P. falciparum P.malariae P. ovale Filariasis Wuchereria bancrofti Culex quinquefasciatus Anopheles sp. Brugia malayi Mansonia sp. Aedes togoi Anopheles sinensis 19

20. 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, n ever 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.) 20

21. 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 A number of Anopheles species are also vectors of filariasis and viral diseases . 21

22. Anopheles: life-cycle Larval habitats vary from species to species, but are frequently exposed to sunlight and commonly found in association with emergent vegetation, such as grass or mats of floating vegetation or algae. The most preferred breeding sites are pools, seepages, quiet places in slow-running streams, rice fields, leaf axils of certain epiphytic plants and puddles of rainwater. Artificial containers, such as pots, tubs, cisterns and overhead tanks are not usually suitable, except in the case of Anopheles stephensi in south-west Asia The eggs, laid singly on the water surface where they float until hatching, are elongated, have a pair of lateral floats, and are about 1 mm in length. Hatching occurs in 2–3 days. The larvae float in a horizontal position at the surface, where they feed on small organic particles. In the tropics the duration of development from egg to adult is 11–13 days. 22

23. Anopheles: behaviour Anopheles mosquitos 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. 23

24. 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. 24

25. Anopheles: health important Important malaria vectors in Malaysia An. aconitus An. balabacensis An. dirus An. donaldi An. flavirostris An. letifer An. leucosphyrus An. maculatus An. minimus An . nigerrimus An. s ubpictus An. sundaicus 25

26. Aedes : Biology Aedes mosquitos occur around the world and there are over 950 species They can cause a serious biting nuisance to people and animals, both in the tropics and in cooler climates In tropical countries Aedes aegypti is an important vector of dengue, dengue haemorrhagic fever, yellow fever and other viral diseases A. aegypti is easily recognized by the contrasting black and white rings on its legs and the lyre-shaped pattern of silver markings on the upper surface of the thorax. A closely related species, Aedes albopictus , can also transmit dengue In some areas Aedes species transmit filariasis 26

27. Aedes : life-cycle The eggs are laid singly on damp surfaces just above or near the water line in temporary pools and other habitats where the water level rises and falls. They can withstand desiccation for many months and hatch only when flooded with water. All species of Aedes which occur in regions with cold winters survive these periods in the egg stage. 27

28. Some species breed in coastal salt marshes and swamps that are flooded at intervals by unusually high tides or heavy rains, while others have adapted to agricultural irrigation practices. Aedes aegypti mainly breeds in the domestic environment: its preferred habitats are water storage tanks and jars inside and outside houses, and roof gutters, leaf axils, bamboo stumps and temporary containers such as jars, drums, used car tyres, tin cans, bottles and plant pots. 28

29. All these habitats typically contain relatively clean water. Aedes albopictus originally occurred only in Asia and Madagascar but recently invaded North and South America, as well as West Africa, where it may become important in the transmission of dengue and other viral diseases. Like Aedes aegypti , it breeds in temporary containers but prefers natural ones in forests, such as tree holes, leaf axils, ground pools and coconut shells, and breeds more often outdoors in gardens and less frequently indoors in artificial containers. 29

30. Aedes : behaviour Aedes mosquitos bite mainly in the morning or evening (crepuscular bitters) Most species bite and rest outdoors but in tropical towns Aedes aegypti breeds, feeds and rests in and around houses. 30

31. Aedes : health important Two important species of Aedes in Malaysia are Ae . aegypti and Ae . albopictus . Both are vectors of dengue/dengue hemorrhagic fever in Southeast Asia 31

32. Culex : Biology About 550 species of Culex have been described, most of them from tropical and subtropical regions Some species are important as vectors of bancroftian filariasis and arboviral diseases, such as Japanese encephalitis The most common species, Culex quinquefasciatus , a major nuisance and vector of bancroftian filariasis , breeds especially in water polluted with organic material, such as refuse and excreta or rotting plants 32

33. culex : life-cycle Rafts of 100 or more eggs are laid on the water surface. The rafts remain afloat until hatching occurs 2–3 days later. Culex species breed in a large variety of still waters, ranging from artificial containers and catchment basins of drainage systems to large bodies of permanent water. 33

34. Examples of such breeding sites are soakaway pits, septic tanks, pit latrines, blocked drains, canals and abandoned wells. In many developing countries Culex quinquefasciatus is common in rapidly expanding urban areas where drainage and sanitation are inadequate. Culex tritaeniorhynchus , the vector of Japanese encephalitis in Asia, prefers cleaner water. It is most commonly found in irrigated rice fields and in ditches. 34

35. culex : behaviour Culex sp is a markedly domestic species The adult females bite people and animals throughout the night, indoors and outdoors During the day they are inactive and are often found resting in dark corners of rooms, shelters and culverts They also rest outdoors on vegetation and in holes in trees in forested areas 35

36. culex : health important Culex quinquefasciatus (vector of Brancroftian filariasis Culex tritaeniorhynchus (vector of Japanese encephalitis-B) Some important Culex sp. as a vector for malaria Culex tritaeniorhynchus Culex fuscocephala Culex gelidus Culex vishui Culex pseudovish 36

37. mansonia : Biology Mansonia mosquitos are mostly found in marshy areas in tropical countries. Some species are important as vectors of brugian filariasis in south India, Indonesia and Malaysia. The body, including the legs and wings, is covered with dark-brown and pale scales, giving it a rather dusty appearance, as if sprinkled with salt and pepper. 37

38. MAnsonia The same mosquito, almost fully blood engorged Adult taking a meal 38

39. mansonia : life-cycle The species that transmit filariasis normally lay their eggs in masses that are glued to the lower sides of plants hanging or floating near the water surface 39

40. Because the larvae and pupae attach themselves to aquatic plants for the purpose of breathing they occur only in water bodies containing permanent vegetation, such as swamps, ponds, grassy ditches and irrigation canals, and may be difficult to find. They can also occur in deeper water where there is floating vegetation, and are very often attached to the underwater parts of floating aquatic weeds 40

41. Larvae of  Mansonia uniformis  attached to plant roots The pupa of  Mansonia uniformis . Like the larvae, the pupa have modified trumpets for piercing plant materials to gain their oxygen. They normally only rest on the water surface like this just before emerging. 41

42. mansonia : behaviour Mansonia species usually bite at night, mostly out of doors, but some species enter houses. Resting after a blood-meal normally takes place out of doors. 42

43. mansonia : health important Important as vectors of brugian filariasis in south India, Indonesia and Malaysia. Serves as a biological vector – it is required for the developmental cycle of the parasite This also known as Elephantiasis 43

44. Prevention and control 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 - Mosquito nets 44

45. Insecticides - The insecticide should be selected for its effectiveness against the target mosquito species - Insecticidal aerosols are sometimes used for the killing of flying and resting insects in situations where immediate results are needed - Because the insecticidal action does not last long it is usually necessary to repeat the procedure several times. - Space sprays are usually applied in and around houses in cities or villages and sometimes on outdoor resting places in dense vegetation or salt marshes - e.g Malathion, Permethrin, Methoprene, Resmethrin 45

46. Prevention of breeding - Source reduction - Such measures include covering or screening water containers, draining ponds and marshes, and filling in ditches, pools, etc - Larvicides - killing immature mosquitoes by applying agents - Insect growth regulators (IGRs) - Microbial larvicides - Organophosphates (OPs) - Surface oils and films - Habitats in and around houses - Habitats in the field 46

47. Biological control - The biological control of mosquitoes and other pests involves introducing into the environment their natural enemies, such as parasites, disease organisms and predatory animals - Fish that eat mosquito larvae can be released into breeding sites - P redatory mosquitoes of the genus Toxorhynchites , the larvae of which feed on other mosquito larvae - Dragonflies, the larvae of which feed on mosquito larvae - Cyclopoid copepods, small crustaceans that attack first- and second- instar larvae of mosquitoes; - Nematode worms that are parasites of mosquito larvae - Fungi that grow in the bodies of mosquito larvae 47

48. Mosquitoes behavior and its implication on control strategies Adult stage - Resting place after taking blood meals (outdoor or indoor)  Indoor e.g Anopheles - Insecticide spraying of walls - Mosquitoes resting on sprayed walls come into contact with insecticide through their feet and are killed. - Some insecticides irritate mosquitoes and cause them to leave houses - Hungry mosquitoes entering a house may bite first and then be killed when resting on a treated wall  Outdoor e.g Mansonia , Culex - Resting after a blood-meal normally takes place out of doors. - Space-spraying - I t has an immediate effect on adult populations of insects and is therefore suitable for the control of disease outbreaks - I t kills mosquitoes that do not rest in houses 48

49. Some species breed in clean water containers in and near houses, whereas others prefer polluted water in sanitation systems, or man-made and natural habitats in rural areas  eliminating or changing the breeding place to make it unsuitable for development of larvae;  making the breeding place inaccessible to adult mosquitos ; - e.g Aedes - Change water in flower vases weekly and scrub to remove adhering mosquito eggs before refilling with fresh water Egg  Larvae Pupae = aquatic stages  releasing fish or other predators that feed on larvae; - mosquito fish ( Gambusia affinis ) and the guppy ( Poecilia reticulata )  applying larvicides  Insect growth regulator 49

50. The larvae and pupae of Mansonia attach themselves to the submerged parts of water plants on which they depend for breathing  removing or destroying the vegetation Many mosquitoes attack people at night inside houses  include the use of aerosols, mosquito coils, vaporizing mats and repellent smoke  Screening of doors, windows and other openings in houses prevents insects from entering, while maintaining some ventilation  Insecticide-treated screening and curtains - Treated screening or curtains provide a toxic barrier to mosquitoes that try to enter houses  Mosquitoes net 50