Dengue-transmitting mosquitoes spread from cities to villages in Amazon

The Aedes aegypti mosquito that transmits dengue virus has mostly been considered an urban mosquito, but a new study of rural communities in the Peruvian Amazon suggests that pattern appears to be shifting.

A Cornell-led team identified Ae. aegypti populations in 29 of 30 sites in urban and rural communities that were surveyed along major river shipping routes between the port cities of Iquitos, Pucallpa and Yurimaguas in the northern Peruvian Amazon.

The paper, “Changing dynamics of Aedes aegypti invasion and vector-borne disease risk for rural communities in the Peruvian Amazon,” appears in PLOS Neglected Tropical Diseases.

“Up until this study, there was an impression Aedes aegypti was largely absent from rural communities, and therefore those communities were not considered a priority for any kind of resource allocation or prevention,” said lead author Kara Fikrig, Ph.D., a postdoctoral researcher in Department of Entomology in the College of Agriculture and Life Sciences (CALS).

Research over a decade ago had revealed initial evidence of Ae. aegypti in some river communities, but since then, no researchers have followed up, thereby maintaining the perception, until now, that dengue was an urban phenomenon.

The mosquitoes hitch rides on boats and disperse among villages along the Amazon River, where some infestations were measured at levels equal to or higher than some of the large port cities where dengue cases persist.

The new infestations are especially concerning as many of these smaller communities lack hospitals or health centers of any kind. In severe cases, such as in patients who develop hemorrhagic fever, care may require a patient being airlifted, which delays treatment and is extremely expensive.

“Our hope is that as evidence accumulates that Aedes aegypti mosquitoes and dengue virus are a threat in rural communities, resources will be allocated there to protect public health,” said Fikrig, who is a former member of the lab of Laura Harrington, professor of entomology (CALS) and a senior author of the paper along with Amy Morrison, a project scientist of pathology, microbiology and immunology at the University of California, Davis.

In the study, the 30 sites ranged from very small communities to urban centers, and mosquitoes were collected at each. After sampling, Fikrig and colleagues noticed that in many of the smaller rural communities, a pattern emerged where Ae. aegypti mosquitoes were present in houses closer to the river ports and absent as houses were further away. The scientists were able to systematically collect samples along transects moving inland in 14 of the smaller communities.

In seven of those sites, they found houses closer to the port were significantly more likely to carry Ae. aegypti adults than those further from ports. Four additional sites showed a similar but less clear trend. Three sites revealed Ae. aegypti mosquito eggs and larvae throughout the town, regardless of the distance from the port, breaking the previous pattern.

Dengue fever symptoms include high fever; severe headache; eye, joint and muscle pain; nausea; and rashes. Severe illness can cause hemorrhagic fever, which can be life-threatening. The virus also has four different strains, called serotypes. When a person becomes infected a second time with a different serotype, their risk of severe disease increases, though they are immune to the original serotype.

“If these communities are just having their first outbreaks now, there will be fewer severe cases, but as they have successive outbreaks, there will be more and more severe cases that require evacuation or, in the absence of evacuation, higher levels of death,” Fikrig said.

In terms of mitigating mosquitoes, the first step is to educate, Fikrig said. A survey of locals in these smaller communities revealed that there were knowledge gaps about relationships between mosquitoes and public health. In cities, health agencies provide constant communication on preventing mosquito breeding, she said. People should learn to limit open standing water in containers, where mosquitoes lay eggs just above a water line, so when water rises, the eggs can hatch. Also, the walls of such containers should be washed weekly.

Chemicals that imitate hormones that block larval development into adult stages and insecticide fumigation are other potential prevention tools, Fikrig said.

In response to these issues, Fikrig has started a nonprofit project, Río Limpio, part of Cornell’s Center for Transformative Action, which seeks to fund community health workers in the Peruvian Amazon to provide vector control support to rural communities.

The Aedes aegypti mosquito that transmits dengue virus has mostly been considered an urban mosquito, but a new study of rural communities in the Peruvian Amazon suggests that pattern appears to be shifting.

A Cornell-led team identified Ae. aegypti populations in 29 of 30 sites in urban and rural communities that were surveyed along major river shipping routes between the port cities of Iquitos, Pucallpa and Yurimaguas in the northern Peruvian Amazon.

The paper, “Changing dynamics of Aedes aegypti invasion and vector-borne disease risk for rural communities in the Peruvian Amazon,” appears in PLOS Neglected Tropical Diseases.

“Up until this study, there was an impression Aedes aegypti was largely absent from rural communities, and therefore those communities were not considered a priority for any kind of resource allocation or prevention,” said lead author Kara Fikrig, Ph.D., a postdoctoral researcher in Department of Entomology in the College of Agriculture and Life Sciences (CALS).

Research over a decade ago had revealed initial evidence of Ae. aegypti in some river communities, but since then, no researchers have followed up, thereby maintaining the perception, until now, that dengue was an urban phenomenon.

The mosquitoes hitch rides on boats and disperse among villages along the Amazon River, where some infestations were measured at levels equal to or higher than some of the large port cities where dengue cases persist.

The new infestations are especially concerning as many of these smaller communities lack hospitals or health centers of any kind. In severe cases, such as in patients who develop hemorrhagic fever, care may require a patient being airlifted, which delays treatment and is extremely expensive.

“Our hope is that as evidence accumulates that Aedes aegypti mosquitoes and dengue virus are a threat in rural communities, resources will be allocated there to protect public health,” said Fikrig, who is a former member of the lab of Laura Harrington, professor of entomology (CALS) and a senior author of the paper along with Amy Morrison, a project scientist of pathology, microbiology and immunology at the University of California, Davis.

In the study, the 30 sites ranged from very small communities to urban centers, and mosquitoes were collected at each. After sampling, Fikrig and colleagues noticed that in many of the smaller rural communities, a pattern emerged where Ae. aegypti mosquitoes were present in houses closer to the river ports and absent as houses were further away. The scientists were able to systematically collect samples along transects moving inland in 14 of the smaller communities.

In seven of those sites, they found houses closer to the port were significantly more likely to carry Ae. aegypti adults than those further from ports. Four additional sites showed a similar but less clear trend. Three sites revealed Ae. aegypti mosquito eggs and larvae throughout the town, regardless of the distance from the port, breaking the previous pattern.

Dengue fever symptoms include high fever; severe headache; eye, joint and muscle pain; nausea; and rashes. Severe illness can cause hemorrhagic fever, which can be life-threatening. The virus also has four different strains, called serotypes. When a person becomes infected a second time with a different serotype, their risk of severe disease increases, though they are immune to the original serotype.

“If these communities are just having their first outbreaks now, there will be fewer severe cases, but as they have successive outbreaks, there will be more and more severe cases that require evacuation or, in the absence of evacuation, higher levels of death,” Fikrig said.

In terms of mitigating mosquitoes, the first step is to educate, Fikrig said. A survey of locals in these smaller communities revealed that there were knowledge gaps about relationships between mosquitoes and public health. In cities, health agencies provide constant communication on preventing mosquito breeding, she said. People should learn to limit open standing water in containers, where mosquitoes lay eggs just above a water line, so when water rises, the eggs can hatch. Also, the walls of such containers should be washed weekly.

Chemicals that imitate hormones that block larval development into adult stages and insecticide fumigation are other potential prevention tools, Fikrig said.

In response to these issues, Fikrig has started a nonprofit project, Río Limpio, part of Cornell’s Center for Transformative Action, which seeks to fund community health workers in the Peruvian Amazon to provide vector control support to rural communities.