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close this bookEmergency Vector Control after Natural Disaster (PAHO)
close this folderPart I: An Overview
View the documentChapter 1: The general problem
View the documentChapter 2: Disaster preparedness
Open this folder and view contentsChapter 3: Postdisaster action
View the documentChapter 4: Vector and Rodent Related Diseases

Chapter 1: The general problem

Although there are a number of' types of' natural disasters, the scope of this ,guide will be limited to those of hurricanes, cyclones, floods, earthquakes and volcanic eruptions. In each ease, the rapidly changing environment produces a general disruption of pasterns of life, which results in stress to individuals and the weakening of' health throughout the population. In many instances, people arc forced into crowded, unsanitary conditions which can lead to outbreaks of' epidemic diseases.

For the public health administrator, sanitarian, entomologist, epidemiologist and vetctor control specialist, the management of health relief' and related responsibilities involves careful planning. Certain natural disasters may provide sufficient warning that some of' their consequences can be alleviated. Predisaster planning, consisting of' the establishment of disaster readiness committees and the formulation of' contingency plans, can limit the risk. This is accomplished through organized preparedness, including the assignment of' responsibilities to specific individuals and the establishment of' intergovernmental relationships through which better use is made of' any existing resources. Contingency planning should, however, be broad enough in scope to allow the response to be flexible. Too much detail may be counterproductive and self-defeating. Certain guides cited in the bibliography provide administrative procedures for planning and organizing public health activities during and following disasters.

'The majority of' vector control programs have static, inflexible administrative procedures. Consequently, there is a tendency to respond routinely to disaster situations, even when they call for innovation and flexibility. A disaster contingency plan may alleviate some, but not all of this problem. As a result, there may be some misdirection, confusion and waste, regardless of' how well organized and adaptable the program is. Overreaction to actual and potential risks of' vector-borne disease may occur because of' our inevitable inability to predict the actual future needs. That this is inevitable should be recognized in determining the availability of resources and the most effective use that may be made of them. In many cases the confusion and overreaction that takes place in the aftermath of a natural disaster will be partially offset by the visibility of entomology and rodent evaluation and control teams, whose presence may benefit the population psychologically.

The life history of Aedes aegypti.

Courtesy Dr. M Giglioli, Cayman Islands

Disasters do not generate "new" diseases but, by altering the environment, they may increase transmission of diseases that already exist in a region through:

(1) Direct effect of the physical event itself, such as fecal contamination
(2) Indirect effects which result in such conditions as overcrowding and poor sanitation
(3) Promoting or causing increase in the movement of populations
(4) Disrupting routine vector control programs
(5) Altering the distribution vector species.

Aedes aegypti breeding sites.

Courtesy Dr. M. Giglioli, Cayman Islands

The increased risk of transmission of vector-borne disease must be seriously considered after all natural disasters. It is a matter of priority, therefore, that the potential of transmission of vector-borne disease is assessed early in the postdisaster period. It is important to note, however, that natural disasters do not necessarily lead to outbreaks of infectious diseases. This is particularly true of the mosquito-borne diseases, since the larval habitats and adult resting sites of mosquitoes often suffer from wind and water damage. As a result, such diseases as malaria, dengue and encephalitis may not appear until several weeks after the disaster, if they appear at all.

Chapter 2: Disaster preparedness

A Disaster Emergency Committee, with responsibility for maintaining a state of' preparedness for natural disasters, should be in existence. Such a committee would include representatives from governmental and private agencies that deal with the routine problems that are accentuated in times of' disaster. A Vector Control Subcommittee should be established in the health sector, and it should be responsible for updating information concerning the status and distribution of' the vector-borne diseases that are endemic to the country, as well as nearby regions. Information should be continually updated on entomological surveillance of' vector populations and on the location and status of manpower, insecticides and application equipment. The subcommittee should be responsible for implementing the emergency vector control operations. To accomplish this, it must have power to act without the bureaucratic constraints that are usual in normal circumstances. The subcommittee may include individuals from a number of agencies within the Ministry of' Hearth, as well as those from other ministries and the private sector. The chairperson of such a committee may be the officer responsible for epidemiology, for malariology or for environmental health.

In areas of high risk of recurrent natural disasters, vector control personnel should attempt to rehearse disaster emergency control operations, in order to refine procedures and develop expertise and a more effective state of alertness. Even without a Vector Control Subcommittee, insect and rodent control personnel can develop a system of alertness to function during and after disasters. Continuous in-service training of all members of the staff should be included in all control programs. Training and program evaluation services offered by the Pan American Health Organization can assist administrators in identifying and resolving problems in control programs.

The vector control program should keep information current on the following:

(1) The status of' all instruments, aids and activities necessary for surveillance, evaluation, and control activities, including:

(a) Distribution maps of areas of' high risk of' disease transmission, which delineate the sizes of vector populations, increases in larval breeding sites and the locations of potential reservoirs of' disease
(b) The distribution of all eases of' malaria of autochthonous and foreign origin
(c) Maps of the phases of' progress in malaria and Aedes aegypti control programs
(d) Population indices for Aedes aegypti, malaria vectors and other important species
(e) Graphs of' monthly variation in vector density per year and according to changes in rainfall and temperature
(f) incidence Graphs showing changes in the incidence of' vector-borne and rodent-borne diseases
(g) Status of seaport and airport Aedes aegypi and rodent surveillance programs.

(2) The inventories of insecticides and vehicles and other types of equipment, and lists of' personnel and variable funds, including:

(a) Breakdowns for each vector and rodent control program
(b) A list of similar or related programs that exist in other ministries, such as Agriculture and Defense, and an inventory of' their equipment and insecticides that can be converted to public health use
(c) A list of' private fumigation and agricultural spray companies that have ultra-low volume (ULV) and other application equipment (which might be owned by resorts or cities in touristed areas)
(d) A list of the names, telephone numbers and addresses of contacts in the Ministry of Health and other ministries and, in addition, of' companies that supply and manufacture insecticides and dispersal equipment and of international representatives
(e) A list of any other known, local sources of expertise, supplies and material .

(3) The status of' transportation, communication and intelligence, and other maps and reports that might assist in reconnaissance and other types of surveys, including:

(a) Road maps of larger political divisions and street maps of cities and towns
(b) Geographical and topographical maps
(c) Aerial photography surveys of high risk areas of vector-borne diseases
(d) Distribution maps of agricultural products
(e) Telephone directories, airline schedules and ham radio operators, and radio, television and newspaper services

(4) Directions for routing requests for interdepartmental and international sect, and a list of agencies.

(5) An operational contingency plan.

Immediate Action

One of the first actions of the subcommittee should be to assess the potential of vector and rodent related problems, and to gather adequate baseline information. Vector and rodent control personnel should be consulted about the locations of temporary living quarters, so that human contact with these organisms is minimized. Vector and rodent control personnel, and sanitarians, c an also provide advice about mosquito and rodent proofing of temporary structures. It is also necessary at this time to determine if the available staff members, insecticide resources and equipment are adequate. If not, appropriate measures should be taken.

Assessment of Situation

A significant problem that administrators of vector control face after natural disasters is accurately assessing the potential of vector and rodent related problems, and determining what resources are required. A considerable amount of unreliable information concerning the vector problem may be generated from other than official sources. In most cases, it will be exaggerated and panic may result in the population. Accurate and updated information collected before a disaster facilitates the proper evaluation of the postdisaster situation and it aids in the process of making logical decisions concerning a plan of action. Such information also helps in providing international relief agencies a clear picture of the problems a disaster can pose. It permits them to reach a clearer definition of their role in relieving shortages of insecticides, rodenticides and equipment. Adequate information from the predisaster period also improves the accuracy of the information that is given to government information services and the local population.

Each of the different types of natural disasters causes specific kinds of vector and rodent related problems, and the periods of time in which they remain problematic varies. This is particularly true of water related disasters that create breeding habitats. Certain types of' information, which may be broken down according to type of disaster, are generally required in the postdisaster period. After all disasters, it is necessary to do the following:

(1) Determine the geographical area and the size and distribution of the population affected, and the political and medical zones involved
(2) Assess the extent of' damage to transportation and communication systems
(3) Determine the availability of staff', the availability and condition of equipment and supplies in the affected area, and the availability of' additional resources in unaffected areas
(4) Review the current information on the vector and rodent situation, including population densities in the affected area and the prevalence of vector and rodent related diseases in affected and adjacent areas.

After the specific occurrence of wafer related disasters, such as hurricanes, cyclones and floods, the following steps need to be taken:

(1) Determine all migrations and redistributions of human populations within and adjacent to the affected area
(2) Assess the extent of damage to the water supply system and sanitary facilities, and estimate the time required to restore these services
(3) Appraise the crowding and exposure to mosquitoes and other vectors in postdisaster living situations, and the rodent-ectoparasite contact and fly breeding as they relate to the living situations
(4) Determine the status of established mosquito breeding habitats and the extent to which new ones are created
(5) Work with epidemiologists and other health officials to reestablish the disease surveillance network and the role of the vector control programs within the network.

When earthquakes and volcanic eruptions occur, these steps should be followed:

(1) Determine population movements and the need for shelter, water and sanitation
(2) Assess the risk of vector and rodent-borne diseases
(3) Determine the need for vector control when there is emergency provision of' water and sanitation in the area.

Aerial observation, where available, is one of the easiest methods of obtaining information on the geographical extent of damage to population centers and communication and transportation systems. It is useful, as well, for assessing vector breeding potential and human population movements. Light, single and multi-engine aircraft and helicopters may be available from the military and private sectors or from commercial agricultural aerial spray companies. Funds for aerial surveillance should be allocated in any budget. Maps and, if available, recent aerial photographs can be used for comparative purposes when the situation is assessed.

Additional information may be obtained from on-site reports from vector control staff members who live or work in the area and from local public health inspectors, physicians, administrators and teachers. Some caution should prevail, however, when interpreting information from these sources.

Determining Priorities of Action

Knowledge of the biology and ecology of pest organisms and their relevance to the current conditions is required when the effect that natural disaster damage has on vector and rodent problems is assessed. For example, flooding usually flushes out or destroys mosquito breeding sites. It subsequently creates additional habitats that can eventually produce even greater mosquito densities. When water and sewage systems are damaged, increased storage of' potable water can provide additional breeding sites for Aedes aegypti while temporary pit latrines can provide habitats for synanthropic flies and Culex quinquefasciatus. Inadequate food storage, poor sanitation, and contamination by debris, animal carcasses and excreta may produce filth flies and increase the visibility of the rodent populations.

Problems related to vectors and rodents may not be confined to the affected region. Human movement away from the region may contribute to crowding in peripheral areas and, as a result, provide opportunity for proliferation of diseases associated with vectors and rodents. Following water related disasters, the peripheral areas may harbor potential mosquito breeding habitats that are more conductive as immediate oviposition sites than in the actual disaster area.

When setting priorities, types of vector-borne diseases in the area and density of the human population are factors to consider. When these are known, action should be immediately directed toward the areas of' high population density, especially slum areas and camps where migrant populations are received. Every attempt should be made to restore and strengthen routine vector control operations within the area.

Under certain circumstances, the Ministry of Defense may be called upon to render aid in the wake of a natural disaster. Probably no other organization is so uniquely endowed with the necessary resources such as manpower and transportation, and possesses the necessary capability of quick reaction.

Urban, suburban, and rural areas of high priority for receiving control efforts should be determined from the following criteria:

(1) Population at risk
(2) Number of confirmed or suspected disease outbreaks
(3) Recent history or disease transmission
(4) Relative density of potential disease vectors
(5) Significant increases in new breeding sites
(6) Significant wind damage resulting in destruction of sprayed houses and increased exposure of displaced or homeless persons to mosquitoes
(7) Presence of potential disease reservoirs
(8) Seasonal accessibility by ground transport
(9) Number and types of complaint calls regarding mosquito activity.

Surveillance and Control

The major activities in vector and rodent control occur during the postdisaster period. If the immediate surveys and other sources of information indicate a potential problem, the sot>ner that postdisaster programs arc implemented to reduce the disease potential, the less is the chance that epidemics will occur and the Iess is the overall expense to the government. Delaying action until an epidemic is at its height can be medically and economically disastrous.

Reestablishing and upgrading routine control operations,, surveillance activities and training of' staff members will go far in lessening the chance and/or impact of' en arthropod-borne epidemic. Operational manuals for control of malaria and Aedes aegypti caused diseases prepared by the World Health Organization and the Pan American Health Organization can assist in planning these activities.

Emergency Action in the Event of a Vector-Borne Disease Outbreak

Should the immediate action to bring vector populations under control prove insufficient, and a vector-borne disease outbreak result, all efforts should be made to reduce infective adult mosquito populations as soon as possible, by such space spray methods as aerial ultra-low volume (ULV) applications, vehicle-mounted and portable thermal foggers, aerosol generators or portable mist ultra-low volume blowers, Details about these methods art given in Part II. under "Specific Vector Problems."

Chapter 4: Vector and Rodent Related Diseases

Mosquito-borne diseases, especially malaria, dengue and arboviral encephalitis, cause significant concern after disasters with which heavy rains and flooding are associated. The immediate effect is, however, the probable destruction of larval habitats and some accompanying reduction of the vector population with the secondary creation of new larval habitats. It is difficult to determine the probability that greater adult densities will be produced in these habitats and, subsequently, whether an increase in disease transmission will occur.

Such vector related diseases as endemic typhus and certain rickettsial diseases, should cause concern when they are already endemic in or near a disaster area. In addition, fly, cockroach, bedbug, human louse and rodent infestations may pose problems. Immediately after a natural disaster, the fly and rodent densities may appear to be greater, either because they become more visible or have indeed rapidly increased. This is partly due to disruption of sanitary services, such as garbage collection and disposal, and also because increased human crowding is accompanied by increases in the densities of populations of rodents and other vermin which seek the same sources of food and accommodation.

In some regions of the world, unsanitary and crowded temporary shelters and inadequate facilities for storing food provide ideal habitats for bedbugs, lice, fleas, mites, mosquitoes and rodents. Under conditions of this sort, the possibility of transmission of diseases such as louse-borne epidemic typhus, plague and malaria is enhanced.

The potential for increase of vector-borne disease occurrence and related problems during a postdisaster period is summarized on the next page. The immediate period is one to seven days after impact. The "delayed" effects refer to those that occur during the next 30 days or more.

The following sections will cover the issues of identification, evaluation and control of specific problems. The reader interested in routine control operations related to specific diseases, should consult the bibliography.




Filth flies


diarrhea, dysentery, conjunctivitis, typhoid, cholera, fly larvae infestation, annoyance


bites and annoyance

encephalitis, malaria, yellow fever (urban), dengue, filariasis, annoyances and bites


rat bites

rat bite fever, leptospirosis, salmonellosis, rat bites


bites and annoyance

epidemic typhus, louse-borne relapsing fever, trench fever, bites and annoyance


bites and annoyance

plague, endemic typhus, bites and annoyance


bites and annoyance

scabies, rickettsial pox, scrub typhus, bites and annoyance


bites and annoyance

tick paralysis, tick-borne relapsing fever, Rocky Mountain Spotted Fever, tularemia, bites and annoyance

Bedbugs, Kissing bugs

bites and annoyance

bites and annoyance Chagas' disease

Ants, spiders, scorpions, snakes

envenomization, bites and annoyance

envenomization, bites and snakes, bites and annoyance

¹ From 1-7 days

²30 days or more