Supplementary reading

The following report does not involve a sudden natural disaster, but describes how a country or region can prepare to cope with the danger of vector-borne disease.

"Emergency Vector Control Procedures for the Americas," a summary from an unpublished report by Drs. M. E. C. Giglioli & R. J. Tonn.

Introduction

Although this communication deals mainly with yellow fever and dengue and in particular with Aedes aegypti, the methodologies discussed apply equally well to the emergency control of other Diptera, especially in urban situations.

The aim of emergency control is to kill as many of the vectors as quickly as possible and, by reducing their density, to interrupt transmission and break the epidemic. In the case of yellow fever, vector control also buys the time needed for an area-wide immunization program, and therefore should be continued for at least ten days after the administration of vaccine.

The essence of emergency control is speed, thus the main thrust of the reaction is directed against the adult mosquito, and not to the more time-consuming and expensive methods of larvicidal control. Similarly, the emergency campaign should be planned and directed by a central command formed by a multidisciplinary council endowed with wide-ranging powers for the duration of the epidemic, as would be the case in times of natural disaster.

The C. V. E.

Each country should give careful consideration to enacting legislation towards the creation of a national "Committee for the Prevention and Management of Vector-borne Emergencies" (C.V.E.), which should enjoy the wide-ranging powers of, and be affiliated to, the national disaster committee.

Ideally this will be a small multidisciplinary executive committee with key representation from the government, armed forces (air), private sector and international aid. selection would be based on professional training and/or management of plant used for insect control sensu Latu (e.g. agriculture, banana growers, etc.) plus senior representatives from the Ministry of Finance and international aid organizations.

This standing committee should be directly responsible to the high-level governmental office both during and between emergencies and should have the legal power to co-opt both temporary members as needed, and stocks and equipment during an emergency.

Terms of Reference

Broadly speaking, these should be:

1. The C.V.E. will formulate a master plan for emergency vector control in their country.

2. Detailed plans and logistics will be prepared for each city and for rural situations. If the disease is not endemic, priority will be given to international points of entry and if it is endemic priority will be assigned to known and potential risk areas.

3. The C.V.E. should institute and keep updated an inventory of national resources for vector control, available from both government and private sectors.

4. In the tight of number 3 above, they should prepare lists of equipment needed, but unavailable, that will have to be found outside the country in the event of an epidemic.

5. The professional manpower resources should be examined, and suitable training of nationals initiated.

6. The epidemiological and vector status of the country must be constantly monitored, in order to determine the state of permissiveness to vector-borne diseases, and to identify the course of any unseasonal rises of unexplained ailments. To cope effectively with this most important function, all hospital returns, sentinel physician reports and vector density and distribution survey summaries will have to be sent to the committee each month and displayed in the committee's office in tabular or graphic form. The more background data (yearly records) the easier it will be to detect abnormal changes in disease and vector density patterns.

7. The identification of gaps in local knowledge, and arrangements for their investigation.

8. The dissemination of incoming epidemiological intelligence, which may threaten the region and the country, to medical and vector control authorities.

9. The identification of ecologically important areas of the country, assigning to them surveillance priorities, in terms of transmission potential, and to allow for these sensitive areas in planning under numbers 1 and 2 above.

10. The preparation of a graded warning system which will trigger an escalating response depending on the gravity of the situation and advising the appropriate officials when such emergency thresholds are reached.

11. Following number 10 above, the C.V.E. will assume the sole direction in initiating and directing countermeasures to the emergency, until the epidemic is arrested, at which time it will resume its monitoring and planning function, updating and improving plans in the light of this recent experience.

When to Declare an Emergency

To a large extent this will depend on the availability of sophisticated diagnostic facilities within the country, and is basically left to the consideration and decision of the C.V.E. of each country (see number 10 above). However, it should not be based only on laboratory-provided, indigenous cases as this may cause long delays.

Obviously if an epidemic is in the region, and vector densities in any country are high and receptive to its transmission, the C.V.E. should act on clinical parameters only,

i.e. hospital and sentinel physician returns, morbidity in armed forces, usual rises in absenteeism in schools, etc. However, for this reason the emergency response should be graded by increasing the tactical use of the control techniques according to an escalating strategic plan, and not on the all or nothing principle.

For example, one can envisage a graded alert, as follows:

Condition Amber. Epidemic in the region; local vector populations highly permissive.

Response: mobilize equipment and manpower, alert physicians and make the threatening disease notifiable. Arrange for the initial release of emergency funds; purchase basic stocks of insecticides. Discuss material and manpower aid that might be needed with international organizations. Notify travellers coming from infected area to report any sickness immediately and treat "sick" houses and their environs with residual and space sprays.

Institute source reduction and other campaigns to reduce vector density in the most receptive areas. Advise the public through the media of the dangers and preventative counter measures.

Condition Orange. Introduced cases increasing, and too scattered to be treated as single foci. Initiate preventative area-wide treatment to cover the distribution of these foci and that of the most receptive urban areas, i.e. high density, low socio-economic levels or other risk parameters.

Condition Red. Indigenous transmission occurring as proved by history of patients' movements; earlier cases now proved by laboratory diagnosis.

Consider spraying the whole city or area on a cycle related to the life cycle and density of the vector until morbidity figures decline radically. In the latter, allow for latency in interpreting results.