Vectors of medical importance

1. Vectors of medical importance

2. Vectors are invertebrates or vertebrate animals capable of transmitting infection from an infected person or animal to another. Vectors harbour the diseases causing organisms , it could either be involved in the life cycle or just be a medium of transmission of the disease causing agent . Transmission could be either mechanical, biological or physical. They can be controlled by use of physical, biological, chemical methods and genetics Recently , integrated methods has been found extremely successful in the control of vectors

3. Examples of vector borne diseases are malaria, trypanosomiaisis, filariasis, viral hemmoraghic fevers, typhus fever , pediculosis, scabies, plague and recently lassa fever. Most vectors are mosquitoes, others are lice, ticks, flies- house fly, chrysops, sandfly, black fly etc , mites and rodents.

4. Many arthropod/insect borne diseases which were thought to have been controlled have been emerging presently. Reasons are insecticide resistance, lack of research in this field, lack of constant surveillance . There is a need for systematic studies on the vectors i.e knowledge on the habitat and habitat of vectors are important

5. Arthropods are broadly classified into 3 classes- Insecta, Arachnida , Crustacea. All have 3 common basic morphology . Distinctive body parts are body divisions, antennae, legs and wings . Insecta- head, thorax and abdomen, 3 pairs of legs, I antennae, one/two wings and habitat is land. Examples are mosquito, flies, fleas, lice and Reduvid bugs

6. Arachnida- has cephalothorax, abdomen, 4 pairs of legs, no antennae, no wings and habitat is land. Examples are ticks ( hard and soft) and mites ( itch mite) Crustacea- has cephalothorax, abdomen,5 pairs of legs, 2 pairs of antennae, no wings and habitat is water. Examples -cyclops

7. Diseases of importance- Mosquitoes- anopheles - malaria/ filariasis Culex- filariasis, Japanese encephalitis, Aedes- yellow fever, dengue fever Flies- housefly- typhoid, diarrheas, gastroeneteritis , giardiasis Sandfly – kala azar, sandfly fever, Oroya fever Tsetse fly- sleeping sickness Lice- typhus, relapsing fever Cyclops- dracunculiasis, fish tapeworm

8. Rat fleas- plague( bubonic) , typhus mites- sarcoptes- scabies, trombiculid mites- scrub typhus Tick- hard tick- viral hemorrhagic fever, rocky mountain spotted fever Soft tick- Q fever, relapsing fever.

9. Characteristics of the vectors

10. Anopheles mosquitoes- Life cycle- it passes through four stages- egg, larva, pupa and adult. Eggs are dark bodies visible and laid in clean water , leaves or steam of aquatic plants Egg stage last two days in favorable conditions Larva is released when egg shell is broken It is an exclusively surface feeder and float just below the surface of water. It is active and shows swift movements It has preference for breeding places like collection of rain water, irrigation dams

11. Larval stage gets completed in 5 days Pupa is also active swimmer, comma shaped and sees with its eyes but cant feed with the mouth. It last 24-48 hours depending on temperature and seasonal factors. Adult – period of oviposition to emergence of first offspring takes 7-10 days It starts mating day one after emergence.

12. Food preference- anthrophilic or zoophilic. Anopheles is both , keeping animals may be protective. Blood meal of female anopheles is essential for maturation of ovum Resting habit- after feeding, female mosquito rest in sheltered place for purpose of digesting blood and development of ovum Indoor resting habits are called endophilic.

13. Anophele mosquitoes cover long distance –0.75-1.5 km Length of life of adult female is 2 weeks It is an important vector in epidemiology of malaria The longer it lives the greater is the chance of being infected or infective. Control- insecticides, larvicides, irradiation

14. Culex mosquito- principal intermediate host of wuchereria bancroft . It is essentially domestic and peri domestic species Egg- laid in polluted water, contaminated with sewage. It is laid in clusters acquired the shape of raft and has micropollar process at one end. Egg stage last 2 days , hatches and larva emerges

15. Larva – long and narrow siphon tube , respiratory openings at the end of siphon tube It has much slower and snake like movement It hangs from surface but not a surface feeder It subsist on bacterial and other organic materials Larva stage lasts 5-6 days Pupa – comma shaped ,stage last 2 days. The period of egg to adult stage takes 8-10 days Egg, larva and pupa are aquatic stages

16. Adult – head, thorax and abdomen, thorax makes an angle with abdomen Flight range- 1.5-2km It is very active in dusk and night Female sucks blood and is anthrophilic Culex quinquefaciatus is prevalent universally , important vector of W. bancrofti. It is anthrophilic and endophagic

17. Control- source reduction is best method Larvicidal measures Control of adult – insecticidal spray Integrated vector control

18. Aedes aegypti is a vector of dengue and yellow fever. It is commonly known as container mosquito ( it breeds in containers) It was initially regarded as urban vector, has now spread to vast rural areas . Breeding habits- storage tanks, receptacles with rain water collected. Life cycles- female lay eggs in containers , eggs is elongate and blackish. Egg when flooded hatch rapidly leading to emergence of larvea

19. Pupa stage last for 24-30 hours leading emergence of adult mosquito Mosquito is of black or blackish brown color with silvery spots and marking. Because of these characters , it is called as tiger mosquito. Adult seek dark and quiet places to rest in bathrooms, bedrooms, kitchen walls, furniture Female mosquitoes bite throughout the day, quite vigorous and bite many persons

20. Flight range – 50-100 metres. Diseases transmitted dengue and yellow hemorrhagic fever. Control- source reduction measures – Do not allow breeding of mosquitoes in discarded containers This requires people participation and education of people. During epidemics, vector control will require the use of space sprays to knock down the infective vector population.

21. Sandfly- head, thorax and abdomen smaller than mosquitoes Wing upright , usually hop and rarely flies Nocturnal pests, live in cevices, holes, store rooms and dark places. Only female bite and hop about breeding sites Life cycle- eggs -7 days, larva 2 weeks, pupa- 1 week and adult 2 weeks. Disease- kala azar Control- insecticide- DDT and HCH , sanitation

22. Tsetse fly-head, thorax, abdomen. Has wings and proboscis Live in vegetaions near woodland LC- female give births to larva every 10 days, pupa- 20-40 days, lifespan 100days Disease- African/ American sleeping sickness Control- DDT, Dieldrin, clear vegetation, genetic control and environmental measures

23. Black fly- head , thorax and abdomen It has wings and proboscis Eggs laid in stones and water weeds, larva is aquatic last 3-4 weeks, pupa 1-3 weeks, adult flight range 100 miles. Disease- Onchocerciasis( river blindness) Control- abate- efficient larvicide

24. Human louse- head, thorax and abdomen. Lay 4-9 eggs per day, last 6-9 days, larva 10-25 days , adult 15-17 days , life span 30-50 days Eggs laid in nits Disease- direct / indirect contact. typhus., relapsing fever, dermatitis. Control- insecticides- DDT HCH, malathion, mass delousing and personal hygeine

25. Rat flea- head , thorax and abdomen Piercing mouth parts Larva-2 weeks, pupa 1-2 weeks. Eggs- 2-6 eggs/egg laying, last 2-7 days, both sexes bite and suck blood, adult- from egg to adult- 3 weeks It lives in nests and burrows, cracks and crevices Mode of transmission- biting ( plague blocked flea bite), mechanical ( host , human, articles), faeces ( fecal drop of infected fly contaminating the skin)

26. Control- insecticides- DDT , HCH, malation Dust /spray applied to floor and walls at a height of 1 feet Repellants Rodent control.

27. Mites charactersitics- less demarcated, head, thorax and abdomen. 4 pairs of legs and suckers on the legs. LC- egg- 2-3 eggs/day adult dies after egg laying, larva matures to nymph in 3 days, nymph 6-8 days, adult- egg to adult- 10-15 days. Lifespan1-2 months Mode of transmission- close contact , contaminated clothes Diagnosis- persistent itch, follicles over the hands, wrist, extensor aspect of elbow, axilla, buttocks, feet, ankles, pals, breast and genitals

28. Possibility of secondary infection Other members of household affected Parasite seen under microscope. Control- use of benzyl benzoate, HCH, permethrin. Personal hygiene

29. Cyclops characteristics- pear shaped , 2 pairs of antennae, legs segmented , eye. It is an intermediate host of guinea worm Man acquires infection by drinking water with cyclops Disease- guinea worm, fish tapeworm Control- physical( boiling), chemical (chlorine, abate), biological ( gambusia), environmental( abolish unsafe source of water)

30. Rats- are classified into two groups- domestic ( Rattus rattus ) and wild rodents Diseases transmitted- bacterial- plague Parasitic- leishmaniasis, chagas diseases Viral – lassa fever Mode of transmission- direct contact- rat bite, indirect contact – through contaminated water and food e.g rat flea or rat urine. Control measures- environmental sanitation, proper disposal of waste, rat proof buildings and elimination of rat burrows

31. Trapping Use of rodenticides Fumigation Chemosterilants Multiple dose poisons- use of warfarins – cause internal bleeding and slow death