Sylvatic to Urban Disease Ecology Project Outline

Under Development

Objective

Understand the ecological dynamics of tropical forest-associated viruses, such as Mayaro Virus, across a land use gradient in eastern Panama in order to model the ability of these virus to penetrate urban areas in tropical America and beyond.

Proposed Team

Matthew Miller, Sam Noble Museum & University of Oklahoma
Sandra Lopez-Verges, Gorgas Memorial Institute of Health Studies
Anayansi Valderrama, Gorgas Memorial Institute of Health Studies Jean-Paul Carrera, Gorgas Memorial Institute of Health Studies Jose Loaiza, INDICASAT-AIP Jorge Garzón, Sam Noble Museum & University of Oklahoma Krisangel López, Sam Noble Museum & University of Oklahoma
Scott Weaver, University of Texas Medical Branch Xiaoming Xiao, University of Oklahoma

Background

Mayaro virus is a single-stranded positive RNA alphavirus (Togaviridae), belonging to the Semliki Forest complex (along with Chikungunya). First detected in French Guiana in 1954, Mayaro virus has been isolated from Cerro Azul in eastern Panama Province from Sabethes mosquitos collected during the day (1966 - Gorgas Institute Report). It has also been isolated from the Maje region.

Mayaro virus is found in diurnal, deep-forest loving mosquitos. As such, it has historically been believed to not present a major risk to tropical urban environments. Hosts are sylvatic vertebrates – mainly non-human primates, but studies show that birds and reptiles are also reservoirs. There are two genotypes, one with broad distribution, the other restricted to Brazil.

Surprisingly, in many rural communities at the forest–agricultural interface, human seroprevalence is high. For example, Abad-Franch et al (2011) found that 44% of Brazilian colonos were seropositive, and that this rate did not vary with sex and age (as you might expect if deep forest penetration were required for infection).

However, more recent studies of the phylogenetic and epidemiological relationships between Mayaro and other viruses such as Chikungunya suggest that it might be move into tropical urban environments, just as the latter adapted to urban Aedes mosquitos.

In the past year, a 30 year old French man was infected with the virus upon returning from French Guiana demonstrating the possibility of geographic expansion of Mayaro beyond the rainforest habitat.

Theoretical justification

The recent outbreaks of Chikungunya and Zika demonstrate an increased risk of formerly sylvatic mosquito-borne viruses emerging from purely sylvatic transmission cycles to urban epidemics that challenge global health.

Likewise Chikungunya and Zika (and dengue) have the potential to revert to a sylvatic transmission cycle in the Americas. Yellow-fever provides a model for what might happen: Yellow Fever was introduced into the Americas in the 17th century, where it began an urban transmission cycle. Vector control and vaccines have eliminated the urban cycle of Yellow Fever in the Americas, yet Yellow Fever persists in the Americas in a sylvatic transmission cycle.

Understanding the ecology of how transmission transitions back and forth from sylvatic to urban transmission cycles is critical in order to get ahead of the curve of emerging mosquito-borne virus.

Eastern Panama, where Mayaro has been historically been recorded, is an ideal natural laboratory for studying the transmission dynamics of mosquito-borne diseases across the forested–urban landscape gradient.

– excellent inventories and research infrastructure for studying vertebrates and mosquito communities, as well as studies of interactions between mosquitoes and hosts

– good land cover and land use data

– expanding urban center and good history of land use change

– good research infastructure with Smithsonian, INDICASAT and Gorgas.

– Panama is an ideal location for this study. Panama has been the site of introduction of new viruses such as Chikungunya and Zika virus in the last two years. And the dynamics of rural-urban human movements on short and long term scales have been well studied. Specifically, the Darien Gap is an international human migratory corridor that because of its forested nature has the ability to promote the long-distance movement of tropical forest pathogens into urban areas in the Americas. Recently, Hotez et al demonstrated that immigrants from Cuba in Texas had leshmaniasis that is believed to have been transmitted during their migration through the Darien Gap.

Preliminary Data

  1. Forest disturbance change mosquito community structure. (Loaiza et al. unpublished)

  2. Navia-Giné, Loaiza, Miller. 2013. Demonstrate that mosquito feeding behavior changes with vertebrate biomass changes. Testing domestic animals may be a critical part of surveillance. And they may be bridge hosts for the slyvatic – urban transition.

  3. Eastwood, Loaiza et al. 2016. Gambia virus isolated from mature forest canopy. Demonstrates important role of forest canopy for enzooic viral circulation.

What do we propose

Work in eastern Panama Land use gradient from Metetí to Panama City includes urban, frontier habitats as well as the only remaining old-growth primary rainforest in Panama (Chagas NP)
Area where Mayaro has historically been detected in Panama Deliverable: Map forest gradient between Metetí and eastern Panama City

Mosquito species composition survey across the land use gradient Deliverable: Map mosquito species composition across landscape

Viral survey across land use gradient Mosquito screening for viruses, canopy and undergrowth
Serosurvey of non-primate vertebrates and humans
How do Mayaro dynamics change (frequency, vector, host) across the landscape gradient
Deliverable: Does the vector species - virus interaction change across gradient

Domestic animal surveys What? Sero-servey or viral survey? Deliverable: Map seroprevalence frequency across landscape gradient

Monkey population density surveys Does hunting reduce monkey populations?
Does this have a effect on viral transmission dynamics?
Serosurveys of wild monkeys not feasible for this grant, but future grants might consider sentinel monkey colonies Is this necessary?

Geographic modeling of risk factors *Still thinking about this…