Disease Prevention Through Vector Control: Guidelines for Relief Organisations - Brossura

Thomson, Madeleine C.

Brossura

ISBN 10: 085598306X ISBN 13: 9780855983062

Casa editrice: Oxfam Pubns, 1995

Riassunto

Over the years, Oxfam has been involved in a wide variety of health-related projects. The Practical Health Guides draw on this experience to put forward ideas on best practice in the provision of health care and services in developing countries The number of refugees and displaced persons has increased greatly in recent years. At least 80 per cent of them are living in tropical or semi-tropical countries where vector-borne diseases, such as malaria, dengue fever and sleeping sickness are common and cause widespread sickness and death in the crowded conditions of refugee camps. This work is intended to help development workers and planners to identify and assess the risks of vector-borne diseases in a camp and to plan and implement cost-effective ways of controlling them. The main vector-borne diseases are described, the importance of identifying the particular disease and its vector and of considering a variety of methods of control is emphasized. The book discusses the need for a community-based approach to vector control, the safe use of insecticides and selection of spraying equipment. Also included are lists of suppliers of insecticides and equipment, sources of advice and recommended texts.

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Informazioni sull?autore

Madeleine Thomson is a researcher at the Liverpool School of Tropical Medicine.

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Disease Prevention through Vector Control

Guidelines for Relief Organisations

By Madeleine C. Thomson

Oxfam Publishing

Copyright © 2013 1995
All rights reserved.

ISBN: 978-0-85598-306-2

Contents

Acknowledgements, 7, 
1 Vector-borne diseases and refugees, 8, 
2 Major vector-borne diseases and their control, 29, 
3 Vector-control strategies, 59, 
4 Insecticides, 83, 
5 Selection of spraying equipment, 97, 
Appendix 1 Addresses of relevant organisations, 107, 
Appendix 2 Addresses of commercial companies, 112, 
Appendix 3 Identification of mosquitoes, 116, 
References, 117, 
Figures and tables, 

CHAPTER 1

Vector-borne diseases and refugees

1.1 Introduction

7.2.7 Refugee populations

Today more than 20 million refugees in countries throughout the world are dependent on international relief assistance. This number has risen dramatically over the last ten years, particularly in Africa, and, sadly, is likely to continue to do so. In addition to refugees, there are large numbers of internally displaced persons in countries such as former Yugoslavia, Rwanda, Afghanistan, Sudan, Ethiopia, Cambodia and Iran. There are over a million displaced people in Central America.

At least 80 per cent of registered refugees and displaced people are living in tropical or semi-tropical countries where vector-borne diseases, such as malaria, dengue, kala azar and sleeping sickness, are common and can have a high case-fatality rate if left untreated.

Outline of this book

The intention of producing these guidelines is to provide refugee relief workers with an overview of the problems associated with vector-borne diseases that they are likely to encounter, and a range of strategies for dealing with them. The type of information required for decision making on vector-control activities is described in section 1, and examples given of the management structures needed for an effective campaign. The major vector-borne diseases and methods for their control are described in section 2. Section 3 presents community-based strategies for vector control. The choice and safe handling of insecticides is outlined in Section 4; and the final section gives recommendations for selection of spraying equipment. In the appendices there is a list of recommended texts; training courses; sources of advice; and the addresses of manufacturers of insecticide, spray machinery, bednets, and insect monitoring equipment.

These guidelines are not meant to be comprehensive but should be a good starting point for those interested in developing and strengthening preventive health-care programmes in refugee camps.

1.1.2 Vector-borne diseases in refugee camps

Vector-borne diseases may be exacerbated in refugee populations for a number of reasons. In recent years falciparum malaria has been a serious cause of mortality in refugee camps on the Thai-Kampuchean border, in Pakistan, and currently in the Rwandan refugee camps in Zaire. It is particulary dangerous when refugees who have not been exposed to the disease before, and therefore have a low level of immunity, are forced to flee into a malarious area (for example, refugees from mountainous regions who flee into malarious lowland areas). Young children and pregnant women are particularly vulnerable to malaria and can suffer very high mortality as a result of infection.

Other vector-borne diseases that affect refugee populations occur as a result of crowded and unhygienic conditions. In recent years louse-borne typhus and relapsing fever have been found in refugee camps in Somalia and Sudan. Louse-borne diseases are not confined to underdeveloped countries, and louse-borne typhus was a major killer of POWs and concentration camp inmates in Europe during World War II. Louse-borne diseases are currently a major concern to health workers in former Yugoslavia.

There are several reasons why vector-borne diseases may represent serious threats to the health of refugee populations:

1 Refugees may lack immunity to a disease or the particular strain of the disease in the settlement area (e.g. malaria).

2 Refugees may have fled through an area infested with certain insect vectors (e.g. tsetse-flies — the vectors of human and cattle trypanosomiasis; sandflies — the vectors of kala azar).

3 Refugees may have settled on land uninhabited by the local population because of insect vectors (e.g. blackflies, the vectors of river blindness).

4 Refugees may have lost their live-stock (in which case insects which normally bite both humans and animals will feed more on humans,).

5 Refugees may live in unhygienic and crowded camps where certain vector populations may dramatically increase. Shortages of water may exacerbate this (e.g. body lice, the vectors of louse-borne typhus and relapsing fever and filth flies which transmit diarrhoeal diseases and trachoma).

6 Stress resulting from flight, fear and loss may exacerbate disease morbidity (e.g. malaria) and may be part of a nutrition-infection-malnutrition cycle. Refugees may have suffered minor or major trauma resulting in blood loss, or be infected with intestinal parasites. The resulting anaemia may make malaria infection life threatening

7 Such problems may be compounded by the breakdown of national vector control programmes in the areas from which the refugees have fled and in the host country. In the host country local resources may be overwhelmed by a sudden influx of refugees.

Vector control and public health measures

Prevention of vector-borne diseases through public health measures in a refugee setting may be more effective in reducing overall morbidity and mortality than curative care. However, all vector control programmes must be seen in the broader context of curative care, immunisation, and diagnostic facilities. Organisations interested in refugee health care should be aware of the risks of vector-borne epidemics, and prepare appropriate control strategies.

1.1.3 Definition of insect pests and vectors

Technical note: By scientific convention all creatures are identified by two names. The first (which always starts with a capital letter) is the 'genus' and the second the 'species' (e.g. Homo sapiens for humans). These specific names are written in italics and are frequently abbreviated with just the first letter of the genus being given (e.g for the mosquito Anopheles gambiae the abbreviated version is A. gambiae).

In order to carry out a control programme against disease vectors it is important to distinguish between those insects, mites, ticks and rats that are merely a nuisance, and those that are mechanical and/or biological vectors. Control programmes are of two kinds: those aimed at reducing a pest population and those aimed at reducing the likelihood of disease transmission. Since some disease vectors are also serious pests, these two categories may overlap.

Nuisance pests

It is their presence in large numbers that defines a pest population as a nuisance. Control measures are generally designed to reduce the pest population or reduce the pest-human contact.

Mechanical vectors

These vectors transmit pathogens by transporting them on their feet or mouthparts. A good example is the housefly that may carry worms, eggs or bacteria from faeces to food-stuffs on its feet and, in this way, transmit diarrhoeal diseases. Mechanical vectors are usually only one of several transmission routes (diarrhoeal diseases are commonly transmitted where there is poor hygiene). Control measures can be designed to reduce the vector population, and to reduce the likelihood of disease transmission, for example, by covering food stuffs.

Biological vectors

These vectors are intrinsically involved in the life-cycle of the parasite or arbovirus (a virus transmitted by an arthropod vector), which must pass through the vector in order to mature to an infective stage capable of being transmitted to its human host. The parasites or arboviruses are acquired from, and are transmitted to, a human or animal host when the vector takes a blood meal. Mosquito vectors are always female since the female mosquito requires a blood meal to mature her developing eggs. In the case of malaria, the parasite usually takes about ten days to mature in the body of the mosquito vector before it is ready to infect a new host. Thus only older female mosquitoes are capable of transmitting malaria.

Because of this, control strategies against malaria vectors can either be designed to reduce the overall population of the vector species, or to reduce the likelihood of the average female mosquito living long enough to transmit the disease.

Both males and females of several other biological vectors, such as tsetse, mites, ticks, and fleas, can transmit diseases, since both sexes feed on host blood. Biological vectors may be a serious threat to health even when their numbers are relatively low.

1.1.4 Factors to be considered in vector-borne disease control

Many different kinds of information will be needed before decisions are made about the need for vector control in a refugee camp: information about the disease problem, about the refugee society, about financial and other resources available, and about the wider implications of vector-borne disease control in relation to the host community. Some of the factors to be considered are outlined below.

Diagnosis and epidemiological data

In many refugee situations the diagnostic facilities are very limited. Information about the most likely causes of 'fever of unknown origin' (including vector-borne disease) should be sought from epidemiological data and clinical symptoms. The setting up of a field laboratory and, in particular, the training of microscopists, are vital components of an effective control programme.

Data should be collected on:

• Who is infected? (adults, children, males, females, new arrivals, old residents). This information may show whether or not transmission is occurring inside the camp.

• Where do the infected people live or work? If the disease is localised, the control programme can be localised too, so that the control effort has the maximum effect.

The importance of training people to evaluate simple epidemiological data is shown in the following case studies: (from M. MacDonald, an entomologist, with UNBRO)

'... last August (1989) there was a frantic call from Site B that we must blast the camp with insecticides. The number of malaria cases seen at the hospital suddenly jumped from less than 100/month to over 500. But when we got up there and looked at the records we saw that all but two dozen were young adult males. It was obvious that there was not an outbreak of malaria within the camp

(In Sok Sann camp a number of children were shown to have malaria). ... when we. ... plotted the distribution of P. falciparum cases in children under 14 we saw that there was a concentration in two sections of the camp. We made sure these sections were well covered with DDT spraying and did some night time barrier spraying with Deltacide and the cases amongst the children dropped.'

Identification and monitoring of vectors

An overall view of the likely pests and vectors to be found should be made on the basis of the known geographic distribution and ecology of the vectors. Within the camp environs, some vector species can be identified using simple reference texts or, if possible, with the help of a vector specialist.

Once the vector has been identified, it should be carefully monitored. Pests are easy to monitor, as their nuisance value is directly proportional to their numbers. Vector species may produce considerable levels of disease even when in relatively low numbers. Monitoring of vector populations by catching the insects when they come to bite people, or when they are resting, or by using some form of trap, will provide essential data on the locality of transmission: for example, are people being bitten while they sleep? Provision should be made for purchasing monitoring equipment. The population levels of certain vector species are closely associated with local climatic changes: rainfall, temperature, and humidity. Rainfall data in particular can be useful in predicting increases in vector populations.

Control strategy in a crisis

The level of response will depend on the seriousness of the situation. Does the epidemic cause a high mortality or morbidity when compared with other health problems? Many vector control programmes in refugee camps are introduced in response to a crisis. Being prepared for such eventualities will make the response much more effective.

By waiting for a crisis to occur before planning a control programme a delay is inevitable and makes it more likely that unsuitable insecticides will be used, because they are the only ones available. Items ordered from overseas may be delayed in customs for long periods. Spare parts for application machinery may take months to arrive and so a selection should always be bought at the time the machine is purchased.

In many cases where vector-borne diseases become a problem there is a 'let us spray everything' mentality. Spray programmes should always be regarded as an adjunct to other control methods (health education, sanitation, environmental health, biological control methods); although, in acute situations, a spraying programme can be initiated prior to any other control activity. Such a programme may be effective in the short term but is unlikely to be successful in the medium to longer term unless other control measures are also utilised.

Sociological factors and public education

While spraying might be a vital component in an emergency, there are important questions to be asked before commencing a control programme. Besides the epidemiological data to determine who is affected, there are sociological factors which need to be taken into consideration at the planning stage. Different cultural habits (such as purdah), and economic factors (availability of cash income) will affect the outcome of a control programme. For example, insecticide treatment of women for lice control may be resisted; bednets may be exchanged for other items regarded as 'more valuable' by the refugees.

Public health education is a major tool in controlling vector-borne disease but is often neglected until a control programme has failed. All vector control programmes require at least the passive if not the active support and involvement of the refugees themselves. Residual spraying of insecticide in dwellings may be refused or washed off if the public are not informed and motivated. Informing refugees about vector-borne diseases, and training them in vector control, can also contribute to health care in the future. Providing information on the hazards of insecticides is also important.

Cost of control programme and choice of insecticide

Control programmes are rarely cheap, although they may be more cost effective than expensive curative programmes. Quality equipment and insecticides bought from well-known firms may be more expensive in the short term but they are recommended because in the long run they are cost-effective and safer.

The choice of insecticides will be determined by various factors: ability to kill the target insect; availability and registration in the country; formulation for particular application method; safety to humans and the environment; and cost.

The use of inappropriate insecticides is not only wasteful of precious resources but may be hazardous too.

Monitoring of programme

When a control programme is introduced, arrangements should be made to monitor its effectiveness. Poor coverage and application practices are two of the main reasons for the failure of control programmes. Many NGO's have a very short 'organisational memory'. Careful monitoring of a vector control programme will enable costly mistakes to be rectified and future programmes to be justified.

Justifying vector control programmes

The quality of health care in a refugee settlement is often superior to that provided to nationals in the host country. This may result in resentment on the part of local residents towards the refugees, and may also undermine the national health infrastructure.

The problems associated with providing refugee populations with health care facilities that are unavailable to the national population have been pointed out by Meek (1989):

'Control of malaria in sub-Saharan Africa is different from south-east Asia in that the frequency of infective bites per person is in many places so high that drastic reductions in mosquito populations would be needed to have any effect at all. Furthermore, very little malaria control is carried out in many African countries because of lack of resources and logistical capacity. It is, therefore, difficult to justify measures in a refugee camp which are not available in the host country, unless the incidence in the camps can be shown to be higher.'

NGO's working in such situations need to take these wider political considerations into account when deciding on a strategy for health care. There are several good reasons which can be put forward to the host community, to justify setting up a vector control programme:

1 Control is part of the national health strategy in the host country.

2 The refugee vector control programme is to be extended to the host community.

3 The level of disease in the refugee community is greater than that in the host community.

4 There is a risk of epidemics.

5 Disease or drug resistance may spread from the refugee community to the host community.

6 Disease or drug resistance may spread from the refugee community to their home community on repatriation.

(Continues...)

Excerpted from Disease Prevention through Vector Control by Madeleine C. Thomson. Copyright © 2013 1995. Excerpted by permission of Oxfam Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Dettagli dell'edizione

• Editore: Oxfam Pubns
• Data di pubblicazione: 1995
• Lingua: Inglese
• ISBN 10: 085598306X
• ISBN 13: 9780855983062
• Rilegatura: Copertina flessibile
• Numero di pagine: 128
• Contatto del produttore: non disponibile
• Persona responsabile: non disponibile