2.4 VECTOR CONTROL

The objective of this section is to provide a basic understanding of vector control in emergency situations. The purpose of a vector control programme is to make the environment unfavourable for the development and survival of the vector. Prevention is better than cure, and when the planning and construction of camps is undertaken, preventing the development of vector problems should be taken into account. Early intervention is always best. For example, when controlling insect vectors, the earlier the intervention in the stages of larval development the better the control that can be achieved. Complete eradication of a vector is rarely possible, but the vector population should be kept to a minimum.

The major biological vectors are mosquitos, flies, fleas, lice, ticks, mites and rodents.

The diseases most commonly spread by vectors are malaria, filariasis, dengue fever, yellow fever, diarrhoeal diseases, trachoma, typhus, sleeping sickness, onchocerciasis and plague.

The main methods of vector control can be classified as personal protection; environmental hygiene; campsite, shelter and food store design and layout; community awareness; residual spraying; and the use of insecticidal powders and rodenticides. Vector control is very specific to the habits of the vector.

It is important to seek the advice of an entomologist/mammalogist/environmental hygienist when designing a vector control programme. This person will assist by:

· identifying the vectors present;
· determining the factors that influence reproduction;
· locating breeding grounds, runs or burrows;
· deciding which control measures need to be taken;
· deciding which chemical control measures to use;
· deciding which chemicals to use;
· deciding the method and interval of application;
· deciding the time and place of application;
· deciding the mixing ratio for the chemical and the situation in which it is to be used; and
· deciding the safety precautions necessary in the storage and use of hazardous chemicals.

2.4.1 MAJOR ARTHROPOD VECTORS AND ASSOCIATED DISEASES

Care should be taken to ensure that any insecticides, rodenticides, etc. that are used in control activities are registered for use in the relevant countries or that permission to use them is obtained from the appropriate government departments.

Mosquitos

Mosquitos are the vectors of malaria, filariasis, dengue, Japanese encephalitis and yellow fever. Table 15 summarizes the associated morbidity and case fatality, and main treatment and prevention measures.

Female mosquitos may feed on a variety of mammals, birds and reptiles, each species having a preference for a particular source of blood. Many species of mosquitos feed on humans, but only some of them are vectors of the diseases mentioned in Table 2.14. Their life cycle involves four stages: egg, larva, nymph and adult. All mosquitos lay their eggs in moist areas, but each species has a specific preference for a given type of area.

The control measures should be specific to the species and their ecological preferences. Table 2.14 presents information on the biological preferences of mosquito species.

The various options for mosquito control are outlined in Table 2.15.

Table 2.14. Diseases spread by mosquitos and their treatment and prevention

Disease	Case fatality	Treatment	Prevention
Malaria Plasmodium falciparum P. vivax P. ovale P. malariae	Often fatal to non-immune people Rarely fatal Rarely fatal Rarely fatal	Antimalarial drugs	· bed nets · repellents · prophylactic drugs · residual spraying · environmental management · monitoring the effectiveness of control methods and the treatment of an epidemic
Yellow fever	Fatal in up to 50% of cases	No specific treatment available	· isolation of infected people · vaccination of the population · environmental management to limit urban breeding sites of Aedes spp. mosquitos
Dengue Dengue haemorrhagic fever	Non-fatal Can be fatal in 10% of cases	No specific treatment available	· isolation of infected people · environmental management to limit urban breeding sites of Aedes spp. mosquitos
Japanese encephalitis	Fatal in 0.5 - 60% of cases	No specific treatment available	· isolation of infected people · vaccination of the population · environmental management
Filariasis	Non-fatal, may lead to elephantiasis	Diethylcarbamazine	· environmental sanitation to prevent breeding of Culex spp. mosquitos in polluted waters

Table 2.15. Biological information on mosquito vectors

Vector group	Vector species	Disease	Typical breeding sites	Resting site	Trans-mission	Blood source	Dispersal range
Anophelines	Anopheles	Malaria, filariasis, arboviruses	Natural pools of unpolluted water	Indoor/ outdoor	Evening and night	Humans and animals	2 km
Culicines	Aedes	Filariasis, yellow fever, dengue, some viral encephalitis	Water containers, small pools of stagnant water	Indoor/ outdoor	Day	Humans and animals	0.1-0.8 km
	Culex	Filariasis, some viral encephalitis	Organically polluted water	Indoor/ outdoor	Day and night	Humans and animals	0.1-0.8 km
	Mansonia	Filariasis	Water	Indoor/ outdoor	Day and night	Humans and animals	0.1-0.8 km

Table 2.16. Choice of control methods for different mosquitos

Mosquito behaviour	Control programme	Vector species	Control of transmission	Control schedule
For all mosquitos	Destruction of breeding sites by drainage or filling	Most mosquito vectors	Totally effective	Permanent
	Larviciding with temephos		2-3 weeks partially effective	Repeated every 2-3 weeks for Anopheles and 2-3 months for Aedes
	Space spraying with pyrimiphos-methyl or deltamethrin	Standard for Aedes simpsoni; also effective for others	Effective Very effective	Weekly Daily in early mornings or evening
	Repellents	All mosquitos	Lasts 1-6 hours with good effectiveness	Apply daily during biting hours
Indoor biting	Screening of doors and windows in house	Anopheles, Culex, Aedes, Mansonia	Partially effective	Put in place when house is built, repair annually
Indoor biting at night	Bed nets Impregnated bed nets with 10-20% permethrin solution	Anopheles, Culex, Mansonia	Partially effective Partially or completely effective	Use bed net, change every 2-5 years Net impregnated with permethrin every 6-12 months
Indoor resting	Indoor residual spraying with pyrimiphos-methyl or deltamethrin	Anopheles, Culex, Mansonia and Aedes aegypti	2-3 weeks partially or completely effective	Every 3-6 months, prior to the transmission season
Mosquito larvae attach to roots of aquatic vegetation	Removal of vegetation, especially water lettuce from all standing water	Mansonia	Partially or completely effective	Check possible breeding sites weekly in the growing season

Lice

There are three types of louse: head, body and pubic. Head lice are not vectors of any particular disease but cause discomfort for those infested. Body lice are vectors of typhus, relapsing fever and trench fever. The presence of pubic lice is associated with sexually transmitted infections, but they are not disease vectors. Body lice are widespread in impoverished communities in temperate climates or in mountainous areas in tropical countries. Head lice and pubic lice are present throughout the world. Louse-borne diseases, associated morbidity and mortality, treatment and prevention are presented in Table 2.17.

Table 2.17. Diseases spread by lice, their treatment and prevention

Vector	Disease	Morbidity and mortality when untreated	Treatment	Prevention
Body lice	Louse-borne typhus	Fatal in 10-40% of cases	Antibiotics Change of clothing Delousing	Change of clothing Delousing Details in Table 19
	Relapsing fever	Fatal in 2-10% of cases non-fatal
	Trench fever	Typically non-fatal
Head lice	No disease			See Table 19
Pubic lice	No disease

Louse-borne infections are common in overcrowded situations, particularly in settlements. Lice are spread via human clothing. Control methods for lice are very simple and effective and are listed in Table 2.18.

Table 2.18. Control methods for lice

Type	Control programme	Control of transmission
Head lice	If shaving is culturally acceptable, adults and children can shave their heads; blades can be distributed to families. Fine combs can also be used. If there are local effective home treatments, such as coconut oil or vinegar, these can be used for small numbers of cases. Pharmaceutical solutions such as malathion can also be used and are recommended during a mass campaign. People with head lice who sleep under impregnated mosquito nets usually lose the infestation.	Delouse new arrivals.
Body lice	Information programme on the dangers of body lice and proposed control methods. Change all clothing. Boil or steam clothing for 15 minutes. Treat non-washable clothing with insecticide and repeat after 1 week. Impregnate clothing with permethrin during rinsing (see below). or For mass campaigns, administer 50 grams of insecticidal dusting powder to each individual in the population via the neck band, waistband and sleeves, paying particular attention to seams and underwear.	Delouse new arrivals. Care should be taken to delouse all feverish persons as well as corpses.
Pubic lice	Pharmaceutical solution, e.g. malathion.	Delouse new arrivals.

Impregnation of clothing with insecticides

Impregnation of clothing with permethrin when rinsing is an effective way of controlling arthropod ectoparasites. Permethrin is safe for this purpose, but if impregnation is carried out the same safety precautions must be used as for impregnating mosquito nets. Impregnation should be done at a central point by trained staff and not by individual families. Clothing treated in this way will retain its insecticidal properties for several washes.

Application of dusts for control of body lice

Application of insecticidal dusts for louse control requires the appropriate apparatus. Simple hand-pumped dusters are available and are moderately effective but not very rapid to use. For mass treatment, powered dusters are more effective but need to be selected carefully. Dusts can easily clog spray nozzles, especially if the air is damp Compressed air is therefore not ideal for pressurizing such equipment. Sprayers powered by carbon dioxide have been devised but are heavy and require supplies of the gas.

Mass dusting programmes require careful planning and staff must be properly trained. The public must be informed carefully about the nature of and reasons for the programme. Staff will need good protective clothing and effective dust masks that protect the whole face.

Flies

Filth flies are considered important vectors of diarrhoeal disease and eye infections. The common filth flies are the housefly (Musca domestica), M. sorbens, the bluebottle and the greenbottle. The housefly and M. sorbens are the most important in the spread of disease. The housefly is thought to be important in the spread of diarrhoea, while M. sorbens spreads the eye infection trachoma. The role of greenbottles and bluebottles in the spread of disease is unknown.

Table 2.19 presents some of the diseases spread by various species of the fly family, and their associated morbidity and mortality, treatment and prevention.

Table 2.19. Main diseases in emergency situations spread by flies and their treatment and prevention

Disease	Morbidity and mortality when untreated	Treatment	Prevention
Diarrhoeal disease (e.g. shigellosis or salmonellosis)	1-10% fatality rate	Rehydration (antibiotics may be needed)	Good personal and kitchen hygiene, safe water and sanitary disposal of faeces
Trachoma	Non-fatal; eye damage, including blindness, in severe untreated infections	Cleaning the eye Antibiotics	Good personal hygiene Adequate supplies of soap and water for washing face and hands

The control of flies is very difficult as they have many breeding and resting sites. The control measures that can be adopted include:

· sanitation: safe faecal and garbage disposal systems
· prompt burial of corpses
· screens for kitchens
· safe food storage systems
· good personal and environmental hygiene.

Mites

Mites are associated with disease, either as vectors or as burrowers into the flesh leading to secondary infections. Scabies and jiggers are examples of burrowing infestations. The trombiculid mite is the vector for scrub typhus. Its breeds in vegetation and transmission occurs during the day. Scabies is the main mite infestation seen in refugee situations. Table 2.20 presents some of the diseases spread or caused by mites and the associated morbidity and mortality, treatment and prevention.

Table 2.20. Diseases spread by mites, their treatment and prevention

Disease	Morbidity and mortality when untreated	Treatment	Prevention
Scabies	Non-fatal but severe cases of infection can lead to eczema	Sulfur ointment or benzyl benzoate	Good personal and environmental hygiene, adequate supplies of soap and water, frequent bathing and laundry
Scrub typhus	1-60% fatality rates	Antibiotic Apply disinfecting lotion to skin Disinfect all bed linen and mattresses	Avoid scrub areas or wear protective clothing or dust with sulfur powder before going into infected areas

Table 2.21 details control measures for mites.

Table 2.21. The choice of control methods for Mites

Type of mite	Control programme
Trombiculid mite	Treat infected persons Locate infested areas ("mite islands") Destroy the mite by destroying scrub areas or spraying with residual permethrin or deltamethrin insecticide spray around houses, hospitals and camp sites

Ticks

Ticks are fairly rare and are unlikely to be a major hazard in emergency situations. Tick-borne endemic relapsing fever is the main tick-borne disease that can afflict humans. The prevention techniques used for malaria usually destroy the tick that causes relapsing fever.

Fleas

Plague and murine typhus are the two main diseases spread by the flea, whose breeding site is the rat. Epidemics of plague occur where there is a high domestic rat population and/or a humid environment at 10-20 °C. The first signs of an epidemic is the occurrence of numerous deaths among domestic rats, followed two weeks later by the first cases of plague among humans. Table 2.23 presents some of the diseases spread or caused by fleas and the associated morbidity and mortality, treatment and prevention.

Table 2.24 details control measures for fleas. The flea population must be controlled before the rat population or the fleas will move to humans.

Table 2.23. Diseases spread by fleas and their treatment and prevention

Disease	Morbidity and mortality when untreated	Treatment	Prevention
Murine typhus	1-5% fatality rate	Antibiotics Insecticide dusting powder for the patient, his/her clothing and bedding Airing of bedding	Good personal and environmental hygiene Regular insecticide use Air bedding regularly Dusting and spraying Prevent conditions that attract an increasing rat population
Plague	50-95% case fatality rate depending on the nutritional status of the population	Antibiotics - streptomycin Chemoprophylaxis for close contacts Quarantine for patients and contacts	Good personal and environmental hygiene Prevent conditions that attract an increasing rat population Vaccination in areas at risk

Table 2.24. The choice of control methods for fleas

Type	Control programme
Flea	First treat rat burrows with insecticide, e.g. pyrimophos-methyl or permethrin, then control rat populations

2.4.2 CONTROL STRATEGIES AGAINST ARTHROPOD VECTORS

The main methods of arthropod vector control in emergency situations can be classified into the following groups:

· residual spraying
· personal protection
· environmental control
· campsite and shelter design and layout
· community awareness.

The choice of control strategies in an emergency situation depends on:

· the type of shelter available - permanent housing, tents, plastic sheeting
· human behaviour - culture, sleeping practices, mobility
· vector behaviour - biting cycle, indoor or outdoor resting.

Vector control is strongly recommended in order to prevent malaria epidemics or minimize their impact. It is essential that any vector control intervention that is proposed should be planned, implemented in a timely fashion and evaluated by qualified technical personnel. It has to be carried out long enough before the transmission season starts to have the expected impact. The overall vector control interventions should be ready to start as soon as possible.

Recommendations for selecting vector control interventions and insecticides will depend on whether the people to be protected are located in temporary settlements, such as camps, or in permanent communities.

Residual spraying

Residual spraying can be conducted indoors or outdoors. It is important to ensure that:

· the community is involved in planning the spraying exercise and is aware of the conditions required for an effective spraying programme;

· painting or application of fresh mud or mortar is completed prior to the spraying exercise;

· the living accommodation and animal sheds of every household are sprayed every six months; and

· the walls, ceiling and roof are covered with the chemical, paying particular attention to corners and crevices.

Outdoor residual spraying is suitable for the control of tsetse flies, thrombiculid mites and sandflies. The important factor to consider during an outdoor programme is that the vector resting sites are clearly identified.

Indoor residual spraying is a recommended technique for controlling mosquitos, triatomine bugs, bed bugs and fleas. It is the most common method in the post-emergency phase when the displaced population is living in more permanent dwellings. The local mosquito vector must be indoor-resting and all houses must be treated, with spraying done at the beginning of transmission season. It will also help to control bedbugs (which live in walls) and may help to reduce flea populations. However, this is an expensive method of control in the long term.

Ground space spraying, either ultra low volume (ULV) cold mist or thermal fogging, is generally not suitable for malaria vector control in emergency situations. It has no residual effect and is not effective against endophilic mosquitos. In the context of camps, especially in crowded areas, ground space spraying can be resorted to if residual spraying is delayed or cannot be implemented. Treatment must be done either early in the morning or in the evening, before people close the shelters for the night. Applications should be repeated at least once a week. Pyrethrins or pyrethroids are the best choice for such application but organophosphate insecticides such as malathion and pirimiphos-methyl are also suitable.

Aerial spraying is not recommended in emergency situations, since it is less effective and very costly.

NOTE: Indoor spraying of residual insecticide ("house spraying") has been the method of control most often used in chronic refugee situations. It is suitable for refugee populations who have built or are occupying mud huts or houses. To be effective the local mosquito vector must be indoor resting (seek expert advice) and the programme must treat all the houses.

- effective in West and South Asia when sprayed at the beginning of the transmission season but less effective in SE Asia

- limited effectiveness in highly endemic parts of Africa

- has to be repeated annually in Asia and at 3-6 month intervals in stable endemic areas; repeated application becomes expensive in chronic emergencies

Insecticide resistance In the context of an emergency, where interventions are planned for limited periods of time until displaced populations can go back home, resistance is not a major concern. Pyrethroids used either for residual application,treatment of nets or space spraying will be effective enough for a few weeks, even if some resistance might occur. The situation would be different for longer-term treatments carried out in permanent settlements.

Personal protection

Personal protection against the spread of disease includes a variety of methods: insecticide-treated nets, personal hygiene, insect repellents and dusting powder.

Insecticide-treated nets (ITNs) are primarily used to protect against mosquito bites; however, they also provide a barrier against the nuisance of rats, geckos and cockroaches.

· Simple bed nets made from man-made or synthetic fibres provide partial protection against malaria.

· The effectiveness of bed nets can be increased by impregnating them with permethrin.

· The bed nets should be soaked in permethrin every six months, or every time they are washed within a six-month period.

· After soaking in the chemical, they should be dried flat so as to maintain an even concentration of the chemical throughout the nets.

· They should be dried flat on the mattresses, as the permethrin will also kill fleas and bed bugs.

ITNs must be available to displaced populations in time to be effective. Distribution of nets must be supplemented by information and educational activities, which may be difficult in an emergency situation. In addition, nets are not easy to hang in tents and are almost impossible to use in shelters. ITNs are regarded more as a tool for long-term prevention, which should be introduced into communities with a number of accompanying measures in order to be effective and sustainable. Free distribution of nets may lead to people refusing to buy nets once they are sold, even at a subsidized price. However, ITNs should be distributed if they are available, especially if house spraying cannot be implemented or has to be delayed. The nets should be treated with insecticide formulations and at dosages recommended by WHO.

Treated sheets and blankets are easy to distribute and effective. In this case, only permethrin (25: 75 cis: trans isomeric ratio) EC or etofenprox EW should be used, at a dose of 1 g/m². Other pyrethroids are not recommended for this type of application for safety reasons and because of possible skin irritation. Treatment can be made by classical dipping or by spraying sheets and blankets laid on the ground, using either a pressurized hand sprayer or a backpack motorized one. The safety of such treatment is well established, and millions of military uniforms are treated every year with permethrin.

Although shown to be effective in a specific epidemiological situation (Afghanistan), the use of treated sheets and blankets has never been tested against malaria vectors in Africa. Since it is always risky to introduce new interventions in emergency situations without previous testing, this intervention is only recommended as a temporary measure or to supplement other well established methods. Insecticide sprayed tents for "transit" buildings, temporary treatment facilities, and family shelters have not been tested outside Asia. The use of insecticide-treated plastic sheeting is promising and undergoing field trials in Angola and Pakistan.

Personal hygiene. Daily bathing, washing of hands after using the latrine, regular washing of clothes, and good food and water storage practices can prevent the spread of fly-, flea- and mite-borne diseases.

· Insect repellents and clothing. Biting by mosquitos, flies and ticks can be reduced by wearing long-sleeved shirts and long trousers, and by using insect repellents. Insect repellents can include traditional repellent mixtures, mosquito coils or commercially produced products. These should be used during the biting hours when the species of mosquito is active. Wearing shoes can prevent infestation with jiggers. Permethrin treated outer clothing worn in the evening or in bed is effective in south Asia but needs testing in highly endemic African conditions.

Dusting powder. Appropriate dusting powders can be used in the treatment of flea and louse infestations. It is important that the powder is applied correctly and that it covers the undergarments and the inner seams of clothing.

Environmental control

Environmental control strategies aim to minimize the spread of disease by reducing the number of vector breeding sites. Some of the most important measures, namely the provision of clean water, the provision and maintenance of sanitary latrines and the efficient and safe disposal of waste, are described earlier in this manual.

Drainage of clean water around water tap stands and rainwater drains is a further important measure in the environmental control of disease vectors. This may include the drainage of ponds, although this may not be acceptable if the water is used for washing

Larvicides destroy the larvae of mosquitos before they mature into adults. Preventing vectors from breeding in this way is far preferable to trying to control them once they have reached the adult stage. Larvicides may be applied via hand-carried, vehicle-mounted or aerial equipment. The chemical is added to water at sites that are recognized breeding grounds, such as ponds or water jars, in areas where the breeding sites are limited in number. This is only a temporary solution, however, as larviciding is generally not cost-effective, especially against An.gambiae and An. funestus. The multiplicity of An. gambiae. breeding sites is such that larviciding is almost impractical. In addition, the efficacy of larvicides is very short (less than a week) and treatment thus requires to be repeated at weekly intervals.

For well localized and accessible breeding sites of An. funestus (permanent swamps with covering vegetation) around camps and residential areas, however, larviciding could be used as a complement to other methods. In this case, temephos would be the preferred larvicide. Pirimiphos-methyl can also be used. Another problem with larviciding is that, even more than for other interventions, the necessary technical expertise and capacity should be available for planning and implementation.

Longer-term measures, such as land drainage or filling, should be planned and implemented to avoid future spraying.

Campsite and shelter design and layout

Site selection is discussed in detail in Section 2.1.1. It is important to reiterate the importance of avoiding areas that are associated with increased incidence of malaria, onchocerciasis (river blindness), schistosomiasis (bilharzia), tick fevers and trypanosomiasis (sleeping sickness).

The following are important aspects of shelter construction.

· Ideally shelters should be of adequate size and spaced sufficiently apart to prevent the spread of communicable diseases.

· The walls should be solid to prevent the entry of, and allow residual spraying of, biting insects.

· Cracks and crevices should be filled, as they are perfect breeding grounds and habitats for certain vectors.

· Openings in houses should never be sited downwind, as this increases the ability of the vector to reach its host.

· A ceiling in the house can block the entry of vectors via the eaves.

Community awareness and health education

Community participation in a vector control programme is essential for its success.

· It allows the implementing agency to develop an awareness of community practices that prevent or encourage the spread of disease.

· Both the community and the vector control team can develop strategies that can be implemented with some degree of success.

· Information on the spread of disease can be disseminated in a culturally sensitive manner.

2.4.3 RODENTS AND THEIR CONTROL

Rodents are disease vectors, reservoir hosts and pests in emergency situations. The main problems associated with rodents are disease transmission, consumption and spoiling of food, damage to stored products, damage to electrical systems, destruction of vegetable gardens, and biting and disturbing people while they sleep. Table 2.25 outlines the main diseases spread by rodents, their treatment, and suggested preventive measures.

Table 2.25. Diseases spread by rodents and their treatment and prevention

Role	Mode of transmission	Disease	Morbidity and mortality when untreated	Treatment	Prevention
As a vector of disease	Rodent urine	Leptospirosis	Low case fatality rates	Antibiotics	Rodent proofing of food stores and containers Good environmental and personal hygiene (e.g. washing of food before eating and storing of cooked food in sealed containers Removal of pools of standing water
	Rodent urine and saliva Food contaminated with rodent body fluids	Lassa fever	15-50% case fatality rate	Antiviral drug therapy
	Food contaminated with rodent body fluids	Salmonellosis	2-3% case fatality among hospital cases	Rehydration Antibiotics in selected cases
	Consumption of rodent meat	Toxoplasmosis	Non-fatal but recurrent	Drug therapy
As a disease reservoir and host to parasite vectors	Fleas and mites - see section 2.4.1 on diseases
	Ticks	Tularaemia	Low case fatality rates	Antibiotics
		Rickettsiosis	15-20% case fatality rate	Antibiotics

The elimination of rodents is difficult but, particularly in densely crowded refugee camps and in villages or towns., the rodent population should be kept to a minimum. Rodent control should include safe and regular garbage disposal, trapping, poisoning in selected circumstances, rodent proofing of stores and careful storage of food.

The control of rodents demands an awareness of the behaviour of the types of rodent found in the area. For example, brown rats tend to display neophobia (fear of new objects) and therefore to avoid newly placed traps, bait points, etc. House mice do not show this type of behaviour. Mastomys rats (the vectors of Lassa fever) tend to avoid brown and black rats and are therefore not usually found in large numbers in urban environments where the latter are common.

Staff undertaking rodent control programmes must be properly trained and given proper protective clothing.

Public awareness campaigns should be undertaken to inform people on how to control rodents and how to detect evidence of increasing rodent infestation.

Garbage disposal

This is discussed in Section 2.3.

Trapping

· Large numbers of traps should be used.

· There are various types of rodent trap; locally available traps may be more suitable for use by the staff and community than imported equipment.

· The bait must be soft; a banana is ideal for attracting rodents.

· Any rodents caught alive must be killed immediately and carcasses burnt.

· Traps must be checked and reset daily.

· Traps must be placed close to areas where rodents seek food, such as food stores and drains, or next to walls or coverings where they tend to move.

· Traps should be used with care in dwellings. Snap traps have strong springs that can damage children's fingers. The action of certain types of trap (e.g. snap traps) can cause the explosive expulsion of bodily fluids, which can be dangerous in the case of certain diseases (e.g. Lassa fever) that are spread in rodent excreta.

Poisoning

· Poisons must be used only in secure areas, such as stores, since there is a danger of children eating the poison or families eating poisoned rodents to supplement their diet.

· If rodenticides are used, the community must be informed and warned not to consume rodents.

· The best rodenticides are the second-generation anticoagulants (e.g. difenacoum, brodifacoum), which can kill rodents after only a single meal. Those used should contain Bitrex, which makes the poison too bitter for human consumption.

· Acute poisons such as red phosphorus and cyanide should never be used.

· Rodenticides based on pathogens such as Salmonella are ineffective and dangerous to humans.

· Rodenticides based on reproductive hormones are not effective.

· Poisoning programmes should always be preceded by the use of insecticides to treat runs and burrows to kill fleas, which would otherwise leave their rodent hosts and attack humans.

· Poisoning campaigns are not effective on their own in the long term. Other rodent control measures, such as removal of rubbish and improvement of food stores, should always be part of control programmes.

· If rubbish has accumulated and rodent populations have built up, a rodenticide programme should always precede the removal of rubbish, otherwise the rodents will tend to move into dwellings and worsen the health problem.

Making buildings rat-proof

· All doors should be as tight-fitting as possible and should have a galvanized steel strip at least 30cm deep attached to the bottom to prevent rodent access. Gaps under doors should be reduced to a few millimetres by careful placement of this metal strip.

· All holes in walls should be filled.

· Any drain pipes should be fitted with rat guards.

· Wiring entering buildings should be fitted with rat guards.

· All windows should be covered with 6-mm chicken wire.

· Vegetation should be cleared from around buildings.

· Overhanging vegetation should be removed.

· Stores must have pallets or shelves for storage purposes.

· All opened food must be stored in airtight containers (preferably metal or metal covered).

Food storage guidelines

· All foodstuffs must be stored on pallets or on shelves off the floor at a minimum height of 45 cm to minimize damage by water or rodents. No pallets should be against the wall as this makes cleaning very difficult.

· Pallets should be arranged in stacks not more than four pallets square, with at least 60 cm between stacks to allow access for cleaning.

· Empty sacks must be stored on pallets and not against wall in piles.

· Opened food must be placed in airtight metal bins.

· The store must be well lit and well ventilated.

· The store must be cleaned daily.

· Food in dwellings should be subject to the same careful storage as that in main stores. If possible it should be stored in rodent-proof (metal or well made wooden) bins, which should be inspected regularly for signs of rodent attack.

2.4.4 MONITORING AND EVALUATION OF VECTOR CONTROL

Successful baseline information has been collected when:

· the vectors prevalent in the camp have been identified;
· the types and incidence of disease caused by these vectors have been ascertained;
· the factors that assist in successful reproduction have been identified;
· breeding and resting sites/burrows for the vector have been identified; and
· suitable control measures have been determined.

Some control measures require their implementation by individuals or family units themselves. The indicators for measuring the coverage of such a programme are:

· the percentage of the population that received the relevant information/education;
· the percentage of the population that implemented the information; and
· the percentage reduction or rise in the vector population.

Chemical control measures are usually implemented by specially trained staff. Some indicators of the coverage of such a programme are:

· the percentage of the target area covered with the chemical
· the supply and safe application of the chemical according to WHO and manufacturer's guidelines; and
· the percentage reduction or rise in the vector population.

The major indicators for measuring an effective programme are when:

· suitable control measures are applied;
· control measures are successful in reducing the vector population and incidence of disease; and
· control measures can be sustained by the population.

2.4.5 FURTHER READING

Equipment for vector control, 3rd ed. Geneva, World Health Organization, 1990.

Kidd H, James JR. Pesticide index: an index of chemical, common and trade names of pesticides and related crop-protection products, 2nd ed. Cambridge, Royal Society of Chemistry, 1991.

Thomson MC. Disease prevention through vector control: guidelines for relief organizations. Oxford, Oxfam, 1995 (Oxfam Practical Health Guide No. 10).

Vector and pest control in refugee situations. Geneva, Office of the United Nations High Commissioner for Refugees, 1995.

Vector control: methods for use by individuals and communities. Geneva, World Health Organization, 1997.