Dengue is the most important arboviral disease of humans with over half of the world’s population living in areas of risk. The frequency and magnitude of epidemic dengue have increased dramatically in the past 40 years as the viruses and the mosquito vectors have both expanded geographically in the tropical regions of the world. There are many factors that have contributed to this emergence of epidemic dengue, but only three have been the principal drivers: 1) urbanization, 2) globalization and 3) lack of effective mosquito control. The dengue viruses have fully adapted to a human-Aedes aegypti-human transmission cycle, in the large urban centers of the tropics, where crowded human populations live in intimate association with equally large mosquito populations. This setting provides the ideal home for maintenance of the viruses and the periodic generation of epidemic strains. These cities all have modern airports through which 10s of millions of passengers pass each year, providing the ideal mechanism for transportation of viruses to new cities, regions and continents where there is little or no effective mosquito control. The result is epidemic dengue. This paper discusses this unholy trinity of drivers, along with disease burden, prevention and control and prospects for the future.

https://www.jstage.jst.go.jp/article/tmh/39/4SUPPLEMENT/39_2011-S05/_pdf

Dengue, Urbanization and Globalization: The Unholy Trinity of the 21st Century

Nonindigenous vectors that arrive, establish, and spread in new areas have fomented throughout recorded history epidemics of human diseases such as malaria, yellow fever, typhus, and plague. Although some vagile vectors, such as adults of black flies, biting midges, and tsetse flies, have dispersed into new habitats by flight or wind, human-aided transport is responsible for the arrival and spread of most invasive vectors, such as anthropophilic fleas, lice, kissing bugs, and mosquitoes. From the fifteenth century to the present, successive waves of invasion of the vector mosquitoes Aedes aegypti, the Culex pipiens Complex, and, most recently, Aedes albopictus have been facilitated by worldwide ship transport. Aircraft have been comparatively unimportant for the transport of mosquito invaders. Mosquito species that occupy transportable container habitats, such as water-holding automobile tires, have been especially successful as recent invaders. Propagule pressure, previous success, and adaptations to human habits appear to favor successful invasions by vectors.

Invasions by insect vectors of human disease

Dengue, a major public health problem throughout subtropical and tropical regions, is an acute infectious disease characterized by biphasic fever, headache, pain in various parts of the body, prostration, rash, lymphadenopathy, and leukopenia. In more severe or complicated dengue, patients present with a severe febrile illness characterized by abnormalities of hemostasis and increased vascular permeability, which in some instances results in a hypovolemic shock. Four distinct serotypes of the dengue virus (dengue-1, dengue-2, dengue-3, and dengue-4) exist, with numerous virus strains found worldwide. Molecular cloning methods have led to a greater understanding of the structure of the RNA genome and definition of virus-specific structural and nonstructural proteins. Progress towards producing safe, effective dengue virus vaccines, a goal for over 45 years, has been made. Images

The dengue viruses.

The number of cases of severe dengue disease continues to grow in endemic areas of southeast Asia, Central and South America, and other subtropical regions. Children bear the greatest burden of disease, and the development of an effective vaccine remains a global public health priority. A tetravalent vaccine is urgently needed and must be effective against all four dengue virus serotypes, be cost-effective and provide long-term protection. In this Review we discuss the unique immunological concerns in dengue virus vaccine development and the current prospects for the development of an acceptable vaccine, a goal that is likely to be reached in the near future.

/pdf/prospects-for-a-dengue-virus-vaccine-54zhcfxely.pdf

Prospects for a dengue virus vaccine.

Investigations of biological invasions focus on patterns and processes that are related to introduction, establishment, spread and impacts of introduced species. This review focuses on the ecological interactions operating during invasions by the most prominent group of insect vectors of disease, mosquitoes. First, we review characteristics of non-native mosquito species that have established viable populations, and those invasive species that have spread widely and had major impacts, testing whether biotic characteristics are associated with the transition from established non-native to invasive. Second, we review the roles of interspecific competition, apparent competition, predation, intraguild predation and climatic limitation as causes of impacts on residents or as barriers to invasion. We concentrate on the best-studied invasive mosquito, Aedes albopictus, evaluating the application of basic ecological theory to invasions by Aedes albopictus. We develop a model based on observations of Aedes albopictus for effects of resource competition and predation as barriers to invasion, evaluating which community and ecosystem characteristics favour invasion. Third, we evaluate the ways in which invasive mosquitoes have contributed to outbreaks of human and animal disease, considering specifically whether invasive mosquitoes create novel health threats, or modify disease transmission for existing pathogen–host systems.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2005.00755.x

Ecology of invasive mosquitoes: effects on resident species and on human health

During the course of an outbreak of dengue type 2 on the island of Tahiti, French Polynesia, severe hemorrhagic disease was observed in an unusual number of patients shortly after the onset of a febrile illness. In at least 33 instances, these hemorrhages were severe enough to require hospitalization and 3 patients died. Gastrointestinal bleeding was the most common type of severe hemorrhage observed and gross hematuria was next most common. The available data suggested that most of the hemorrhagic episodes were etiologically related to dengue virus.

An epidemic of dengue on Tahiti associated with hemorrhagic manifestations.

Prior laboratory studies and field observations suggested that it might be possible to reduce the size of the population of, or eliminate, Aedes polynesiensis by the introduction of Aedes albopictus. The former mosquito is the principal vector of nonperiodic filariasis caused by Wuchereria bancrofti and the latter is a closely related species refractory to the development of human filariae. The practicability of such competitive displacement was studied by a field trial on a remote coral atoll where there was an established population of A. polynesiensis. Three strains of A. albopictus were liberated at separate localities on the atoll and their fate was followed for 4 years. One strain disappeared within 12 months after release and the other two disappeared within 48 months. It was not clear whether A. albopictus failed to become established because the strains were unsuitable, the general environment was inappropriate, or A. polynesiensis was present in such numbers that A. albopictus rarely succeeded in mating with its own species.

Jacques Saugrain

Papers

An epidemic of dengue on Tahiti associated with hemorrhagic manifestations.

A field trial of competitive displacement of Aedes polynesiensis by Aedes albopictus on a Pacific atoll.