Category Archives: Dengue

Malaria, Dengue, Mosquitoes – evolving in the urban environment

As the world increasingly urbanizes, we need to address the role of urban ecosystems and the evolution of disease vectors and organisms.  Marina Alberti and colleagues explained that …

“Recent studies show that cities might play a major role in contemporary evolution by accelerating phenotypic changes in wildlife, including animals, plants, fungi, and other organisms. Many studies of ecoevolutionary change have focused on anthropogenic drivers, but none of these studies has specifically examined the role that urbanization plays in ecoevolution or explicitly examined its mechanisms.”

In their own study they looked at “five types of urban disturbances including habitat modifications, biotic interactions, habitat heterogeneity, novel disturbances, and social interactions.” The researchers learned that, “clear urban signal; rates of phenotypic change are greater in urbanizing systems compared with natural and nonurban anthropogenic systems.” They concluded that there is need to continually “uncover insights for maintaining key ecosystem functions upon which the sustainability of human well-being depends.”

Of particular concern in the area of tropical health are the unique urban manifestations of diseases like yellow fever, dengue and malaria. Although Zika virus, for example, was first discovered in forests, it has adapted to an urban cycle involving humans and domestic mosquito vectors in tropical areas where dengue is endemic. Musso and Gubler in their review further explain that although there may be sylvatic cycles of Dengue, “Arboviruses such as DENV have adapted completely to humans and can be maintained in large tropical urban centers in a mosquito-human-mosquito transmission cycle that does not depend on nonhuman reservoirs.”

Weaver et al. note that Zika in spreading to Asia, “emerged on multiple occasions into urban transmission cycles involving Aedes (Stegomyia) spp. Mosquitoes.” In addition it can be hypothesized that phenotypic changes in Asian lineage ZIKV strains made rare disease outcomes such as congenital microcephaly and Guillain-Barré more common and visible.

According to Estelle Martin and co-researchers, “Puerto Rico, a major metropolitan center in the Caribbean, has experienced increasingly larger and clinically more severe epidemics following the introduction of all four dengue serotypes.” They found that Dengue serotype 4 replaced earlier strains and that “this epidemic strain progressed rapidly, suggesting that the epidemic strain was more fit, and that natural selection may have acted on these mutations to drive them to fixation.”

In addition to virus evolution, mosquito changes have been documented by Caroline Louise and colleagues in “One of the world’s largest urban agglomerations infested by Ae. aegypti … the Brazilian megalopolis of Sao Paulo.”  They detected microevolution despite a short observational period and stress the implications of the “rapid evolution and high polymorphism of this mosquito vector on the efficacy of control methods.”

“The adaptation of malaria vectors to urban areas is becoming a serious challenge for malaria control,” is a major concern of Antonio-Nkondjio and co-workers. They found, “rapid evolution of pyrethroid resistance in vector populations from the cities of Douala and Yaoundé,” Members of this team also learned that the M form of Anopheles gambiae predominated in the centre of urban agglomerates in Cameroon. Previously it was known that larval habitats polluted with decaying organic matter as found in densely populated urban agglomerates, were unsuitable for Anopheles gambiae. The recent study showed that the “M form showed greater tolerance to ammonia (arising from organic matter) compared to the S form. This trait may be part of the physiological machinery allowing forest populations of the M form to colonize polluted larval habitats.”

The evolutionary response of vectors and disease organisms to urban environments needs continued monitoring. Urban disease control and elimination efforts must adapt to such adaptations in the disease process.

Decreasing Household Costs of Dengue Prevention at Low-Altitudes in Colombia …

… Redirecting Resources into the Hands of People Who Slap Mosquitoes Everyday.

Class members from the course “Social and Behavioral Foundations of Primary Health Care” at the Johns Hopkins Bloomberg School of Public Health write a policy advocacy blog as part of their assignments. Here we are sharing the blog posted by . read more on this and other SBFPHC blog posts by clicking here

Squito(Photo by James Gathany)

Colombia bears high burdens associated with dengue.  During the 2010 epidemic, disability-adjusted-life-years lost were 1178.93 (per 1 million inhabitants) versus just 88.38 averaged for 2011-2012.  Rodriguez et. al (2016) estimated economic burdens higher than $129.9 million USD each year, with most of the burden at the individual household level (46%, 62%, and 64%) for preventing/controlling mosquitos.

The Colombian Ministry of Health and Social Protection uses the 1,800m elevation mark when allocating money to low-altitude departments for dengue-related expenditures.  This suggests that only half of Colombia’s 47 million residents are at risk for dengue.  However, many people vacation at low altitudes where they risk becoming infected and bringing dengue back home.  If low-altitude residents were better equipped to control mosquitos, then both residents and visitors would be better protected.  Unfortunately, low-altitude residents shoulder a greater financial burden for mosquito prevention than the government.  Rodriquez et al. (2016) reported that almost $85 million USD was the highest household burden (for prevention alone) between 2010 and 2012, while the highest government burden was only $35 million USD (for prevention, awareness campaigns, and control combined).

If the Ministry of Health and Social Protection’s vision of equity-based protection and healthcare resources for all is to come to fruition, more money must flow into prevention and control.  Residents should not have to buy expensive sprays when they already live in poverty.  If Ministry-controlled finances were earmarked for inexpensive yet effective household supplies, such as curtains and water container covers, then less money would be required for treatment.  I advocate for reshuffling some of the dengue-related funds to reflect the prevention priority; increase amounts for household prevention and decrease treatment allocations.

Let’s not make low-altitude residents choose between buying expensive sprays or food to eat.  It’s hard enough already just to slap together supper.