Dengue Information

A Historical Background

See also An Update of Dengue Fever in the Caribbean - 1998

These cases in Belize represent the first confirmation of dengue virus type 3 in a CAREC member country since 1963, when this specific serotype was laboratory confirmed in Jamaica. In the years following, dengue virus type 2 was the only identified virus type circulating in our sub-region. The type 1 virus was introduced in 1977 and subsequently resulted in a Caribbean-wide pandemic of dengue fever. It should be noted that dengue virus type 3 was last isolated in the Americas in Puerto Rico during 1978, while the type 4 virus was first identified in the subregion during 1981.

After an absence of sixteen years, dengue virus type 3 reappeared in the Americas, first in 1994 in Nicaragua. During the years following, its spread has been documented in Panama, Costa Rica, Honduras and Mexico. Gene sequencing of dengue 3 isolates from Panama and Nicaragua has indicated that these virus strains are identical to the dengue 3 serotype that caused major epidemics of dengue hemorrhagic fever (DHF) in Sri Lanka and India in the 1980s. These new dengue 3 strains have also been shown to be genetically distinct from the dengue 3 strains found previously in the Americas (Gubler and Clark, 1995).

Over the last twenty five years, dengue virus types 1, 2 and 4 have become endemic in the Caribbean sub-region, producing numerous epidemics at irregular intervals. Within recent years, however, progressive shortening of the inter-epidemic period has been observed with major outbreaks occurring every one to five years. Co-circulation of these three dengue virus types is occurring in many islands such that dengue fever can be described as hyperendemic in the sub-region.

The Implications of Dengue - 3 Introduction

As with the introduction of dengue virus type 1 into the sub-region, the potential for a Caribbean-wide pandemic due to the type 3 virus is real because an extremely high proportion of the population are immunologic virgins to this specific serotype. Additionally, in our sub-region where populations have been repeatedly exposed to infection with dengue serotypes 1, 2 and 4 within a relatively short period, the introduction of the type 3 virus would significantly increase the probability of emergence of epidemic dengue hemorrhagic fever (DHF)/ dengue shock syndrome (DSS) in the Caribbean.

The Required Action

An acute sense of political urgency is required to galvanise the necessary human resources and commitment as well as to mobilise the necessary finances to ensure either a high degree of preparedness or prompt and efficient outbreak control.

Vector Control

Source reduction and other environmental manipulative strategies, such as the covering of essential containers, the disposal of non-essential containers and the removal of natural breeding sites must be vigorously pursued as the immediate

And primary tools for vector control. Source reduction may be coupled with larviciding methods limited to those domestic-use containers that cannot be eliminated, destroyed or otherwise managed.

Entomologic surveillance must be maintained in order to determine changes in the geographic distribution of the vector, to obtain relative measurements of the vector population over time and to facilitate appropriate and timely decisions regarding interventions. Vector surveillance would also assist in the monitoring of insecticide susceptibility.

Epidemiologic Surveillance

Passive surveillance systems which allow for the legal notification of clinically suspected and confirmed cases of dengue fever, DHF and DSS to national epidemiologists, epidemiology units or other appropriately designated agencies responsible for communicable disease surveillance should already exist in all dengue-endemic countries.

However, in order to enhance the early detection of dengue virus type 3 in a population, we would strongly advise that an active fever alert system be established in each of our member countries. Health centres and hospital Accident and Emergency Departments within the public and private sectors should monitor and report the total numbers of persons attending that centre together with the total number of febrile cases (those with temperatures of 38 degrees C or greater) on a weekly basis. This data should in turn be consolidated and analysed at both the regional and national levels.

If this specific system is not feasible, then at least 30 percent of a region’s [parish, county] health centres should be selected on the basis of high clinic attendance, high vector densities in the catchment area, and efficient communications with the diagnostic laboratory.

A predetermined number of blood specimens should be drawn from a representative sample of febrile patients seen at any health station for early dengue virus detection. In this regard, blood samples should be collected from some proportion of patients (5 to 10 percent) who present with fever, headache and any third symptom that is compatible with dengue fever. In order to optimise the probability of virus isolation, blood specimens should be obtained from patients within three days post onset of illness.

CAREC will shortly be circulating more detailed guidelines relating to the collection, handling and processing of clinical specimens in support of public health surveillance.

Proactive, laboratory-based surveillance is essential to provide public health officials with information on certain aspects of dengue virus activity, including:

the different virus serotype(s) in circulation the distribution of circulating virus types by time the geographic distribution of circulating virus types within a population.

Other Laboratory Support

As thrombocytopenia and haemoconcentration are essential diagnostic criteria for the confirmation of cases of DHF/DSS, it is very important that hospital laboratories are appropriately equipped to perform serial haematocrits and platelet counts, each at least daily. It should be appreciated that when all of the designated clinical criteria, including these two, are not verified, suspected cases of DHF/DSS cannot be classified as confirmed.

Communication Strategies

It is extremely important that pertinent information on the epidemiology of dengue fever; the clinical diagnosis and management of all forms of the disease; and appropriate vector control measures be communicated to all the relevant stakeholders in well-balanced, non-alarming messages which will facilitate public health action, engender community participation, etc. Key stakeholders would include political and technical decision-makers, medical personnel, the media, members of the tourism sector and other economic partners and the public.

National preparedness must be the watchword of all stakeholders as the late initiation of emergency control measures in the face of an outbreak do not significantly reduce morbidity and may result in mortality that was avoidable. An evaluation of existing resources (human, financial and infra-structural) for vector-control, optimal patient care and management, epidemiologic and entomologic surveillance, etc., as well as their organisation and sustainability must be undertaken and the identified needs appropriately addressed. For example, contingency plans should be formulated to convert schools or other public buildings into clinical facilities should the need arise.

Conclusion

The high frequency of international and regional travel related to tourism, labour, commerce and other activities increases the probability of importation and introduction of dengue virus type 3 into our territories. Existing high Aedes aegypti indices will enhance the potential for virus transmission in our populations. All member countries are therefore being urged to pay careful attention to this new epidemiologic development and to begin to plan to address it even at this time. CAREC will continue to monitor and provide additional updates as the situation evolves.