Vector-borne diseases and refugees

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...