Report on the status of Aedes aegypti in the Americas

(1)

regional committee

PAN AMERICAN

_WORLD

HEALTH

_HEALTH

ORGANIZATION

_ORGANIZATION

XXII Meeting _{XXV Meeting}

Washington, D.C. October 1973

Provisional Agenda Item 25 _CD22/6 _(Eng.)

6 September 1973 ORIGINAL: SPANISH

REPORT ON THE STATUS OF AEDES AEGYPTI ERADICATION IN THE AMERICAS

More than 20 countries and territories of the Americas, containing 80% of the total initially infested area, had succeeded in eradicating the vector by the start of the last decade. The state of the continental pro-gram deteriorated from 1964 to the present, due primarily to the continued infestation of some countries on the Continent and to the neglect of erad-ication surveillance activities in some countries that had been free of infestation. A gradual decline in interest and in the commitment to erad-ication in certain countries that remained infested led to an unfavorable balance between newly cleared areas and reinfested areas.

As of mid-1973, eradication of the vector was being maintained in the following countries and territories: Argentina, Bermuda, Bolivia, British Honduras, Chile, Ecuador, Nicaragua, Paraguay, Peru, Uruguay, and the Panama Canal Zone. Brazil has succeeded in eliminating the reinfesta-tion of its northern region. While keeping large areas free of the vector, Mexico has a reinfested area on its border with the United States of America.

Costa Rica has cleared its foci of reinfestation. Panama, still considered free of the vector, has a focus of reinfestation.

Thus, the situation in mid-1973 is that Aedes aegypti is eradicated in 8.5 million km2

, or 72%, of the 11.8 million km originally infested in the Americas.

The 3.3 million km2 _{that remains infested, equivalent to 28% of the} originally infested area, is distributed among 34 countries and territories and includes the reinfested areas of Brazil, Costa Rica, Guatemala, Mexico, and Panama.

Of these 34 countries and territories, 22 have nationwide campaigns under way, six are making limited efforts at eradication, two are in a preparatory phase, and four have no activities under way or have had their campaigns interrupted.

The following is a summary of current information on the efforts of the governments and of the Organization in each of the countries and ter-ritories still having an Aedes aegypti problem.

(2)

CD22/6 (Eng.) Page 2

Barbados. The campaign was reorganized in late 1968 and in the first half of 1969. Activities thenceforth were conducted in accordance with the

plan of operations and the standards of eradication.

In 1971 the program, which was achieving good results, suffered a decline in field personnel, and hence in the pace of progress.

In mid-1973, 49 of the country's 61 localities are negative, and Aedes aegypti persists in 12 localities, but with an infestation index of only 0.06%.

Brazil. This country completed eradication of the mosquito in 1955 and was declared free of Aedes aegypti in 1958. In 1967, however, the city of Belem, Capital of Para State, and several neighboring localities were found to be reinfested. In August 1969, three cities in Maranhao State - Sao Luis, Ribamar, and Anil - were also found to be reinfested.

The Government took immediate steps to delimit the precise extent of the problem, prevent transportation of the vector to other areas of the country, intensify the surveillance of the localities most exposed to rein-festation, and eradicate the mosquito in the reinfested areas.

The renewed eradication campaign was intensive and adequately sup-ported and enjoyed the Government's unstinting commitment. As a result,

the infestation index in Belem, Sao Luis, and the other 48 localities near those two cities was reduced to zero; the entire reinfested area was cleared. From three to five verification cycles have been carried out in the area, and have given negative results for Aedes aegypti.

Brazil's surveillance service has not found Aedes aegypti in any other part of the country.

Colombia. The deterioration of conditions manifested itself in the reinfestation of Barranquilla and Cartagena, discovered in 1969. When bud-getary limitations reduced the intensity of the campaign in 1970 and 1971, the vector spread throughout much of the country's northern region (the Caribbean coast). An inspection of over 300 localities revealed the pres-ence of the vector in 105 localities in nine departments, mainly along the Caribbean coast, in La Guajira, and in the city of Ccuta.

The campaign was reorganized in the second half of 1972. Despite the inadequacy of its resources (coverage of 50% of the infested area), it is showing significant accomplishment as of mid-1973: the infestation in-dex has been reduced from 15.5% to 1.2% in Barranquilla, from 33.4% to 4.3% in Cartagena, and from 10.5% to 0.1% in Monteria.

(3)

Costa Rica. Declared free of Aedes aegypti in 1958, this country did not maintain a regular service for surveillance of the vector. When surveillance was renewed at the start of 1971, reinfestation was discovered in the city of Puntarenas, the country's chief port on the Pacific.

The campaign was reorganized forthwith. Inspection of other areas revealed that the port cities of Limon and Golfito and several localities near them were also reinfested.

Thanks to the Government's interest and commitment, the index in the eight localities had dropped to zero by the start of 1973; the three foci of reinfestation were eliminated.

An entomological survey seeking the vector in areas with an environ-ment favorable to it is 80% ahead of schedule, with negative results.

Cuba. The campaign is being conducted by the general public health services in the provinces of Pinar del Rlo, La Habana, Las Villas, and part of Matanzas. Means to attack the vector exist in 40% of the total infested area, and the results are limited.

Dominican Republic. The country remains infested, but is conducting no activities.

El Salvador. This country completed its eradication campaign in 1957 and was declared free of Aedes aegypti in 1960, but reinfestation was discovered in a section of the city of San Salvador in June 1965. Subse-quent investigation revealed that the reinfestation extended to the entire city and its surroundings, and that many other areas of the country were reinfested as well.

The campaign was reorganized in July 1965. Due to budgetary limi-tations, however, its activities have been restricted to the city of San Salvador and the Ilopango international airport, with limited results.

Guatemala. Guatemala eradicated the vector in 1958 and was declared free in 1959. In late 1972 the eradication surveillance service discovered another focus of reinfestation in the same city (near the border of El Salvador) in which a reinfestation had been eliminated in 1967.

Another locality on the border with El Salvador was found to be re-infested in early 1973, and the city of Chiquimula on the Honduran border was found positive in May 1973.

(4)

Guyana. Phase I of the eradication plan, including the city of Georgetown, the areas to the east and west of the Demerara River, and the eastern coastal region, has continued. The initial infestation index, ranging from 17% to 59%, was down to 0.5% in the first half of 1973. The Government plans to clear the area completely and move into Phase II during 1973.

Haiti. The campaign continues without interruption.

Honduras. This country completed eradication in 1959 and was de-clared free the same year. In 1968 the surveillance service discovered that the cities of Puerto Cortes and San Pedro Sula, in the north of the country, were reinfested. As a result of this finding, surveillance in other

locali-ties exposed to reinfestation was intensified. Six localilocali-ties near San Pedro Sula and the city of Nueva Ocotepeque, on the El Salvador border, were found to be reinfested.

The Government reinitiated the campaign immediately. Due to budget-ary limitations, however, only the city of San Pedro Sula and a few nearby

localities were treated, and the results were limited. At the end of 1971, the Government decided to suspend the campaign for lack of resources.

However, the vector has been spreading through the country's interior since 1968; it occupies large areas today. The Government decided to renew the campaign in the first half of 1973. A budget of US$250,000 made it possible to begin treatment in three northwestern departments and in some localities in the Sula Valley.

The Government is drawing up a five-year plan of operations for the purpose of assuring that the campaign will be financed in the coming years.

Jamaica. The Governnent began eradication activities in the city of Spanish Town in 1970, but has not yet decided to make the campaign nationwide.

Mexico. This country completed eradication of Aedes aegypti in 1961 and was declared free of the mosquito in 1963. A surveillance service es-tablished in that year has periodically inspected the localities most ex-posed to reinfestation. Since then, the Aedes aegypti problem in Mexico has been limited to reinfestations in the area of the border with the United States of America.

Despite the efforts made, it has still not been possible to eliminate the reinfestations which, according to epidemiological research, appear to stem from Aedes aegypti introduced from the United States of America.

(5)

effective action is not taken in a short time, the entire country will soon be reinfested.

Panama. This country completed eradication in 1955 and was declared free in 1958. In 1969 the city of Col'on and three neighboring localities were found to be reinfested. After this reinfestation was eliminated and an entomological survey and special inspection of the entire country were carried out, it was discovered in October 1972 that Aedes aegypti had been reintroduced in the nation's capital by used tires imported from a still infested country.

The Government immediately renewed its attack activities and aug-mented the campaign's budget for 1973. Work is continuing with highly favorable results.

Trinidad and Tobago. The attack phase, designed to eliminate foci of reinfestation in Port of Spain and nearby areas, is continuing in Trinidad.

On the island of Tobago, a surveillance service is maintaining the eradication of the vector.

United States of America. From its initiation in 1964 the campaign covered the Aedes aegypti infested areas only partially. The infested areas include all or part of ten southeastern states, Puerto Rico, and the U.S. Virgin Islands. Since the coverage of these areas was inadequate, very

limited results were achieved by the campaign up until 1968.

The Government later decided to terminate the program. Eradication activities on the mainland, in Puerto Rico, and in the Virgin Islands came to a complete halt in July 1969.

Venezuela. The campaign has continued to focus on the country's western region, especially the border with Colombia, and has had limited

results. The Government has not yet decided to extend the campaign to all infested areas.

France

Guadeloupe and Martinique. The campaigns are active here, but the results are limited because eradication standards and procedures are not adequately observed.

(6)

Netherlands

In the Netherlands Antilles, the island of Bonaire, having achieved an index of zero, has entered the consolidation phase. The islands of Aruba, Saba, and St. Eustatius have also achieved a zero index and should soon enter the consolidation phase.

Progress has been slow in St. Martin, and Curarao is now in the preparatory phase.

In Surinam the campaign in the city of Paramaribo and in the coastal region is enjoying somewhat better results than in 1971. The infestation index has dropped from 4.2% to 2.5% in Paramaribo.

In Surinam, the main obstacle to progress, other than administrative difficulties, is the development of Aedes aegypti in rainwater conduits in the homes. About 40% of the houses in Paramaribo have this type of problem. A solution is difficult to find; several methods of treatment have already been tried to little avail. Among the efforts to date have been the use of

teams with ladders, the use of Abate in muslin bags, and the use of Abate in hardened bars. A plan to use a combination of perifocal treatment and aerial spraying of a new insecticide, Sumithion, in ultra-reduced volume, is now under study.

The Organization worked with the Government of Surinam in 1972 on an entomological survey of special types of breeding places of Aedes aegypti

in the country.

United Kingdom

The campaign is in a very advanced phase in St. Lucia. Of the 27 localities there, 24 are negative, while Aedes aegypti are found in three localities, with an overall infestation index of 0.1%.

Favorable results are being achieved in Montserrat, where the infes-tation index has declined to 1.4%. The same is occurring in Grenada, where the index has fallen from 27% to 2.5%.

The campaign is progressing in St. Vincent and Dominica, despite ad-ministrative problems that have been encountered. The infestation indices have declined from 25% to 1.9% and from 17.7% to 2.4%, respectively.

The campaign's progress in Antigua and Anguilla has been slow because it has not as yet been possible to overcome the vast administrative and operational problems (relating to the meeting of standards and to staff supervision and management).

(7)

Government and the Organization in 1972. In mid-1973 the surveillance

service discovered a small focus of reinfestation in the city of Georgetown, Grand Cayman. The Government promptly took the necessary measures to elim-inate the focus.

Activities in the Bahamas are limited, while the preparatory phase is coming to an end in the British Virgin Islands.

The Turks and Caicos Islands are in the organizational phase of their campaign, while a feasibility study is under way on St. Kitts and Nevis.

It should be recalled that urban yellow fever caused severe harm to the population of the Americas until the early decades of this century. The latest outbreak took place in Trinidad in 1954. Though eradication of the vector and other measures have done much to control this type of yellow

fever, the disease has not lost its significance. Annual reports of cases of the jungle form of the disease in several countries of the Continent and the epidemics resulting from frequent migrations of the virus in epizootic waves through extensive areas make it clear that the problem has not been

solved. The existence of extensive areas of the Americas still infested with Aedes aegypti greatly expands the risk that urban foci of the disease will reappear.

Between 1950 and 1972, 2,304 cases of yellow fever were reported in 14 countries of the Americas; four of the cases were of the urban type, while the rest were of the jungle type. Epidemics of the jungle type were

recorded in Venezuela in 1972 and in Bolivia, Brazil, and Peru in 1973. A total of 92 cases was reported up to July 1973, with 19 in the Cochabamba and Santa Cruz areas in Bolivia, 40 in the states of Goias and Mato Grosso in Brazil, 31 in the areas of Puno and Huanuco in Peru, and two in Colombia.

Epidemiological surveillance of the disease is constantly declining in intensity and in geographic coverage; the same is happening with

viscerotomy.

Of the diseases transmitted by Aedes aegypti, dengue may now be the most important call on the attention of the Governments of the Americas. The 88,173 cases of dengue reported in eight countries and territories in the 60's are certainly far below the actual number. The northern (Carib-bean) coastal region of Colombia was struck by an epidemic due to the

Type II virus between 1971 and 1972; on the basis of an epidemiological investigation, the number of cases was estimated at slightly over half a million. In a 1971-72 cost-benefit study by Arthur D. Little, Inc., on

(8)

The discovery that the Type II and Type III dengue viruses have been active in the Americas in recent years increases the concern and the respon-sibility of the Continent's governments for fear of a sudden appearance of the hemorrhagic form of the disease, with or without shock, in the countries and territories still infested with Aedes aegypti - the only known vector of the disease.

Beginning with the I Meeting of the Directing Council in Buenos Aires in 1947, the Organization's Governing Bodies, in successive resolutions, have urged infested countries and territories to complete the eradication of Aedes aegypti as soon as possible, since the success of the continental program can be assured only if the current sources of reinfestation in the Americas are rapidly eliminated. The XVIII Pan American Sanitary Conference

(1970) ratified the earlier recommendations of the Governing Bodies. The III Special Meeting of Ministers of Health of the Americas (Santiago, October 1972), considering:

(a) that jungle yellow fever will persist in countries in the enzoo-tic area of the disease;

(b) that the existence on the Continent of areas still infested with Aedes aegypti will keep some countries in constant danger with respect to urban yellow fever;

(c) that there is no evidence that dengue will cease to be a problem in the coming years in the countries of the Region still infested with Aedes aegypti; and

(d) that evidence of the activity of two types of dengue virus in some countries and territories increases the concern over the possible appearance of hemorrhagic dengue,

recommended the eradication of Aedes aegypti in the Ten-year Health Plan for the Americas (Official Document No. 118).

In fulfillment of the resolutions of the Governing Bodies, the Organization in recent years has conducted activities aimed at coordinat-ing, stimulating and accelerating eradication efforts. Among these activi-ties have been:

(a) Conference on Eradication of Aedes aegypti in the Americas, held in Washington, D.C., April 3-5, 1967. Almost all countries in the Hemisphere were represented. The Continent's eradication program was thoroughly reviewed.

(9)

CD22/6 (Eng.)

Page 9

which have slowed the progress of the campaigns, to examine mea-sures that could be taken to overcome those difficulties, to dis-cuss plans for simultaneous, coordinated campaigns in the infested

countries and territories, and to make recommendations on the organization and maintenance of surveillance services in areas

freed of the mosquito.

(c) Working Group on Aedes aegypti Colonies in Laboratories. A group of experts on this subject met in Washington, D.C., July 17-19,

1967. It made highly specific recommendations on the elimination of colonies and on the basic requirements for the maintenance of colonies considered essential.

(d) Intensive technical assistance to the countries and territories in the planning and organization or reorganization of their

campaigns. Collaboration in personnel training and program evaluation.

(e) Provision of limited quantities of equipment, insecticides, vehi-cles, and supplies as motivation to certain infested or reinfested countries and territories.

(f) The First Meeting of the Scientific Advisory Committee on Dengue, held in Washington, D.C., in January 1970, reviewed the status of dengue in the Americas and laid the foundations for a program of surveillance of the disease in the Continent.

(g) Study Group of the Pan American Health Organization on the Pre-vention of Diseases Transmitted by Aedes aegypti. At a meeting in Washington, D.C., February 9-14, 1970, it reviewed in detail the strategy for preventing the diseases transmitted by Aedes

aegypti and the methods employed and available for controlling or eradicating it. It also defined the basic elements of a

cost-benefit study of the different situations.

(h) Second Meeting of the Scientific Advisory Committee on Dengue, held in Port of Spain, Trinidad, in April 1972. It reviewed the

status of dengue on the Continent and the status of the program of surveillance of the disease. It also reviewed the standards and procedures for investigation of epidemics of the disease and recommended the intensification of dengue surveillance activities in the Region.

(i) Cost-benefit Study on the Prevention of Diseases Transmitted by Aedes aegypti in the Americas (1971-72). Made by an independent

(10)

In short, the status of the campaign in the Continent's 45 countries and territories initially infested by the vector is as follows: eradication

is being maintained in 11 countries and territories; campaigns are under way in 28; two are already negative; nine are in an advanced stage of

erad-ication; the campaigns of six are making good progress; seven are making slow progress; and activities in six are limited. Two others are in a preparatory phase, and there are no activities in four.

The absence or shortcomings of vector surveillance services in some countries or territories which have eliminated the vector are also contrib-uting to the establishment of foci or areas of reinfestation. The Organiza-tion is cooperating with several countries and territories in their review of surveillance plans and of the standards and procedures for carrying out those plans and in the training of auxiliary technical and professional personnel.

Despite the efforts made, much remains to be done before the conti-nental program to eradicate Aedes aegypti is completed. The countries must therefore provide the conditions necessary for their programs to carry out the entire process leading to eradication, as identified by the Working Group on Eradication of Aedes aegypti in 1967. These conditions are, basi-cally, the following:

(a) A firm decision by the Government to eradicate the mosquito and to accept the responsibility involved in achieving this end.

(b) A sufficient budget to meet the needs of the campaign for person-nel, equipment, and supplies without interruption until the

mosquito is eradicated.

(c) A nationwide organization adequate for the satisfactory conduct of the program throughout the country.

(d) The administrative autonomy and flexibility necessary for the program to manage its budget without bureaucratic obstacles, to set the rules governing the work of its personnel, to determine salaries and travel expenses, and to accept, shift, sanction, or dismiss personnel without delay or difficulty.

(e) The legal support which endows the campaign with the authority to enforce its decisions and to execute, without delay, the measures needed to eradicate the mosquito.