We have developed a pair of stochastic simulation models that describe the daily dynamics of dengue virus transmission in the urban environment. Our goal has been to construct comprehensive models that take into account the majority of factors known to influence dengue epidemiology. The models have an orientation toward site-specific data and are designed to be used by operational programs as well as researchers. The first model, the container-inhabiting mosquito simulation model (CIMSiM), a weather-driven dynamic life-table model of container-inhabiting mosquitoes such as Aedes aegypti, provides inputs to the transmission model, the dengue simulation model (DENSiM); a description and validation of the entomology model was published previously. The basis of the transmission model is the simulation of a human population growing in response to country- and age-specific birth and death rates. An accounting of individual serologies is maintained by type of dengue virus, reflecting infection and birth to seropositive mothers. Daily estimates of adult mosquito survival, gonotrophic development, and the weight and number of emerging females from the CIMSiM are used to create the biting mosquito population in the DENSiM. The survival and emergence values determine the size of the population while the rate of gonotrophic development and female weight estimates influence biting frequency. Temperature and titer of virus in the human influences the extrinsic incubation period; titer may also influence the probability of transfer of virus from human to mosquito. The infection model within the DENSiM accounts for the development of virus within individuals and its passage between both populations. As in the case of the CIMSiM, the specific values used for any particular phenomenon are on menus where they can be readily changed. It is possible to simulate concurrent epidemics involving different serotypes. To provide a modicum of validation and to demonstrate the parameterization process for a specific location, we compare simulation results with reports on the nature of epidemics and seroprevalence of antibody in Honduras in low-lying coastal urbanizations and Tegucigalpa following the initial introduction of dengue-1 in 1978 into Central America. We conclude with some additional examples of simulation results to give an indication of the types of questions that can be investigated with the models.

A simulation model of the epidemiology of urban dengue fever: literature analysis, model development, preliminary validation, and samples of simulation results

Over the last four decades, a number of arthropod-borne infections have been recognized for the first time. Some have become of considerable public health importance, such as dengue hemorrhagic fever (DHF), and others are spreading geographically and their incidence is increasing. There has been an important recrudescence of several long-known vector-borne diseases. Malaria, leishmaniasis, dengue, and plague have resurged in numerous foci, in some cases where they were thought to be under effective control. In most instances, the appearance of new diseases and syndromes and the resurgence of old can be associated with ecological changes that have favored increased vector densities. Dam construction, irrigation and other development projects, urbanization, and deforestation have all resulted in changes in vector population densities that appear to have enabled the emergence of new diseases and the resurgence of old diseases. Greatly increased human travel has spread infectious agents, introducing them into areas in which they had been hitherto absent. It is essential to understand the factors that caused increased vector densities and hence the transmission of disease to prevent the emergence and resurgence of more diseases, as well as to serve as a basis for effective control.

Emerging and resurging vector-borne diseases

Numerous insects and other arthropods colonize and reproduce in disturbed and man-made environments. This is particularly apparent in Juban areas. The extent to which these organisms exploit urban environments has only recently been appre­ ciated. Our ignorance in this area can be attributed, in large part, to the general dearth of relevant ecological studies. The purpose of this review is to evaluate and synthesize information important to an understanding of the ecological bases for the reproduction and survival of insects (and to a lesser extent other arthropods) in urban environments. More specifically, we emphasize the need to assess two major components of the insect's environment: resources necessary for survival and the pervasive influence of man. Population, community, and evolutionary case-history studies are analyzed within this conceptual framework. Comparative studies in more than one habitat are given special consideration. Finally, suggestions for future studies on basic and applied questions in urban entomology are offered. Information on insects in urban environments is scattered throughout the agricul­ tural and biological literature. This is not surprising since most of the information has been gathered by specialists in a wide variety of fields. Examples of these fields and representative studies include: ecological and environmental sciences (56, 64, 81, 92, 117, 118, 137, 138, 159, 165, 166), population genetics and evolutionary biology (14, 17, 18,36,38-41,75,99, 151), general pest identification and control (43, 72, 150), biological and integrated control (91, 107, 108, 121, 122), forest entomology (25, 50, 51, 71, 91, 103, 130), plant pathology (53, 143), medical entomology (61, 85, 99, 124, 149, 157), stored-product entomology (10, 19,49, 70, 88, 102, 168, 174), and insecticide toxicology (16).

Ecology of insects in urban environments

This paper is an attempt to synthesize information available on C. p. quinquefasciatus in Africa. The latter is presently found in most urban areas of the African continent and in rural settlements which show some trends towards urbanization. In East Africa, and the islands of the Indian Ocean, C. p. quinquefasciatus is one of the major natural vectors of Wuchereria bancrofti. In addition it can also transmit, under laboratory conditions, some other pathogenic agents.Preimaginal forms develop in different kinds of man-made breeding-places, especially those containing polluted water. The situation in each African region is reviewed in detail.Female behaviour during the different phases of the gonotrophic cycle is analysed, together with population dynamics.Control methods by synthetic insecticides are discussed in relation to resistance problems and the characteristics of the breeding sites. Other control methods based on the use of growth regulators, genetic manipulation, biological agents (parasites and predators) and environmental management have been investigated as well. Most of them cannot be easily applied or are not yet applicable for control operations.

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Biology and control of Culex pipiens quinquefasciatus Say, 1823 (Diptera, Culicidae) with special reference to Africa

In the town of Makunduchi, Zanzibar, wet pit latrines provided breeding places for Culex quinquefasciatus and there were few other mosquito breeding places available. The adult mosquito population in bedrooms was monitored for a year and found to consist almost entirely of Cx quinquefasciatus of which 2.45% carried infective larvae of Wuchereria bancrofti. It was estimated that each person received about 24,993 bites per year, of which 612 were potentially infective. After a year of baseline data collection, polystyrene beads were expanded in boiling water and applied to form floating layers on all infested pits. Subsequently the adult mosquito population declined remarkably so that the estimated number of bites per person per year was only about 439. To retain control, surveillance for newly wet pits continued to be necessary. Initially the microfilarial rate in the human population was 49.5%, with many cases of filarial disease. The microfilarial rate was reduced to 10.3% by mass treatment with diethylcarbamazine, with no sign of resurgence a year after treatment. The infective rate among mosquitoes was reduced to 0.41% and the combined effect of the vector and microfilarial control was to reduce the number of infective bites per person per year by 99.7%.

Control of Bancroftian filariasis by integrating therapy with vector control using polystyrene beads in wet pit latrines.

(1973). Mosquito‐borne disease problems In reply to: The urbanization of tropical countries. C R C Critical Reviews in Environmental Control: Vol. 3, No. 1-4, pp. 455-495.

R.F. Peters Chief

Papers

Mosquito‐borne disease problems In reply to: The urbanization of tropical countries