The scientific journal Communications Biology, belonging to the Springer-Nature Group, has just published an open-access article paper entitled “Yellow Fever Surveillance Suggests Zoonotic And Anthroponotic Emergent Potential,” describing research conducted by the Biogeography, Diversity, and Preservation Group of the Department of Animal Biology of the University of Malaga (UMA) in Spain that inquires into the evolutionary dynamic of the global risk of yellow fever transmission to humans. This paper also investigates the geography of the influence of other primates and certain mosquitoes on transmission in forest regions of America and Africa. These mosquitoes –not any mosquito, the Aedes aegypti and the Aedes albopictus, the tiger mosquito--act as vectors of yellow fever, both in zoonotic transmission--which occurs from non-human primates to humans--and anthroponotic transmission--between humans. According to these scientists, contact between non-human primates and humans, exacerbated by deforestation, is increasing, and hence the risk of new viral variants emerging and reaching human population. This paper of the UMA evidences an important potential role of primates in the transmission in southeastern Brazil, an area where no yellow fever cases seem to have occurred for decades, but where there have been frequent cases in recent years. The paper is signed by PhD student Alisa Aliaga, as main author, together with Raimundo Real, Jesús Olivero, Marina Segura, and Carlos Marfil-Daza. It has been prepared in collaboration with the International Vaccination Center of Malaga, which belongs to the Ministry of Health.
Yellow fever is a disease caused by a flavivirus that is present in tropical and subtropical areas of Africa and South America. The Biogeography Group of the University of Malaga justifies the need for this research based on the fact that globalization through travelers who transport the virus, as well as the expansion of mosquito vectors help new virus lineages spread and increase the risk to human health. That is why knowing how the risk area of this disease is changing on a global scale is necessary in order to prevent and respond efficiently to the occurrence of new outbreaks.
The results of the research predict that, in South America, the zoonotic potential (i.e., from non-human primates) for yellow fever transmission covers regions in western, eastern, and central Amazon basin, and also great part of the Atlantic Forest of Brazil (“Mata Atlantica”). In Africa, this potential may affect some areas in the north of the open and forested savannas and south of the Central African rainforests.
The involvement of non-human primates on transmission to our species in regions like southeastern Brazil, and the high evolutionary rate recently shown by this pathogen, might result in new variants that could reach human populations, taking into account that the zoonotic cycles are closely connected with urban areas.
Forest fragmentation tends to amplify the risk of disease transmission by increasing the proximity of human populations to wildlife. The paper proposes a list of primate species to be considered in case yellow fever surveillances in these species were addressed. These primates belong to 13 genera in South America and 11 genera in Africa, in which the yellow fever virus has often been detected, and which geographic distribution coincides with the distribution of human cases.
Three Yellow Fever Transmission Geographic Scenarios
These analyses can contribute to identify new areas that could be prioritized for vaccination, for which the scientists propose to take three yellow fever transmission geographic scenarios into account.
The first one describes areas with very favorable conditions, for both the presence of the virus and mosquito vectors. This is the case of some areas of West Africa, Central Africa, and southern Brazil. The models provide support for the vaccination program planned by the Brazilian Health Ministry in 2019 in many states in eastern Brazil, despite the fact that vaccination in this area is not yet considered by the World Health Organization (WHO) and the Center for Disease Control and Prevention (CDC) to be a priority.
The second scenario describes areas with low--but not negligible--risk of yellow fever transmission, which are located in the north of Namibia, the west of Zambia, the east of Ethiopia, and some areas in Somalia. The WHO and the CDC do not consider vaccination in these areas to be a priority.
Finally, the third scenario describes areas environmentally favorable to the presence of mosquito vectors, but not to the virus occurrence. This situation occurs, for example, in North America, Southern Europe, Asia, and Oceania, which are outside the yellow fever endemic area. In this situation, the most suitable management policy should consist in preventing virus introduction by international travelling. There are countries that do not require the yellow fever vaccination certificate for travelers, and yet are located in high-risk zones in which vaccination is recommended by the WHO. In addition, citizens entering in countries at high or medium risk of yellow fever transmission should be required to be vaccinated. In areas with stable yellow fever vector populations that are close to the endemic areas, vaccination should be also considered an option. The vaccination program of the WHO in the provinces of the north of Argentina are positive examples to be followed in this respect.