Arbovirology, Arbovirus, Arthropod-borne virus, these are informal name that refers to all virus types infecting “blood sucker” arthropod vector, capable to multiply the virus and to transmit it to vertebrates through their bite. These virus-vectors are essentially mosquitoes (male only), ticks and sandflies feeding mainly on mammals and sometime on other vertebrates (e.g. birds, reptiles). However, some virus types can exclusively infect arthropods and do not replicate in vertebrates, they are namely “host restricted insect-specific viruses”, some of them are genetically closed the well-known virus families (Flaviviridae, Togaviridae, Phenuiviridae) harboring highly pathogenic arboviruses (e.g. Dengue virus, Western equine encephalitis virus) for vertebrates. Do these close virus parents have the potential to jump into vertebrate as a new potential host and generate another emerging disease? Also, can we use these viruses as a tool to eventually aid the prevention of arbovirus transmission and protect the populations against arbovirus threat? . Only the continuous efforts of scientific research will allow us to answer.
Once upon a time, Zika was just a forest in Uganda. Today, it is known to most as a disease-causing virus, but many do not truly understand that it has journeyed from one of many anonymous and undiscovered, yet widelycirculating viruses with zero to minimal pathogenic characteristics within mammals, to one of the most notorious viruses spread by mosquitos in the world. And though this has been an unlikely journey, any virus has the potential to undergo such a similar transformation. To understand Zika’s journey is to understand the nature of arboviruses, their frequent-neglected status with respect to disease surveillance, and their potential to emerge as severe public health risks.
Many people understand that there are mosquito-borne illnesses that are spread by viruses, but it may come as a surprise that there are thousands of viruses that are spread by mosquitos that can infect humans. The overwhelming majority of these infections do not cause disease, either because they are not capable of proliferating within the human ecosystem, or they are easily overcome by our immune systems, or in some rare cases, the disease they produce is undetectable or inconsequentially mild. The sheer number of these viruses make it difficult to justify funding for research or surveillance for every virus, much less a virus that does not cause disease in humans. This was precisely the case for Zika prior to 2015 when it emerged in the Americas-one of several viruses known to circulate among mosquitos and non-human primates, which posed no significant risk of illness among humans.
From the recent article on “Exploiting the Legacy of the Arbovirus Hunters” , it is clear that “a generational gap has developed in the community of arbovirus research.” This has several origins, with the well-recognized one starting in the early 1980s, when the HIV pandemic suddenly moved the resources and the scientists away from arbovirology to a neglected field of retroviruses, also, with a positive impact by funding the emerging biotechnologies successfully accompanying the domain (Pathogen Molecular detection). Since these times the historical richness of field-oriented virus discovery was reduced. Moreover, since the 1990s, new technologies (i.e. Next generation sequencing) resulted in an increase of virus discovery-more new virus sequences that novel virus isolates-that is changing our understanding of the virus world and dramatically impair the field of arbovirology toward eco-epidemiology-viruses and natural hosts suspected or unknown-and the fundamental of the immune response. Nevertheless, this oxymora of relentless tide of “big” data generated by sequencing, too often partially described or understood, had a negative impact for public health when the goal is to promptly detect and characterize emerging arbovirus pathogenic for human or animal. As an example, within a five years study period, of mosquito and tick collection in China, 28 non-dengue and non-Japanese encephalitis viral strains were isolated from different places and confirm to be pertain to the classical arbovirus Togaviridae family . All these new isolates belong to a family known to harbor highly pathogenic viruses for human and animals and need to be finally characterized for their potential threat for human and animals. New arbovirus continues to be persistently isolated in China and their extension more accurately known .
Nevertheless, Arbovirus are spreading and will spread with their vectors , while arbovirology is shrinking. As an example, taken by these authors “The global population at risk from mosquito-borne diseasesincluding dengue, yellow fever, chikungunya and Zikais expanding in concert with changes in the distribution of two key vectors: Aedes aegypti and Aedes albopictus. The distribution of these species is largely driven by both human movement and the presence of suitable climate.” Indeed, human exponential growth of the population, all sorts of exchanges restlessly increasing in number and intensity (trade, travel, migration, etc.), as well as climate change and virus-mosquito transportation in permissive previously naïve environment (e.g. the classical of infected mosquitos’ eggs transported by sea), all are concurring as main drivers of arbovirus spread and outspreading endemicity.
Nonetheless, it is difficult to forecast which arboviruses will become public health threats when there so many to choose from, and so many that are innocuous to humans. But this is precisely the paradox that many public health decision- makers face: how do you determine which of the multitude of arboviruses to surveil or research, when any of them can emerge as threats to humans? Most would agree that we would benefit from some advanced warning on what could be “the next Zika”. This advanced warning, though, comes from proper arbovirus surveillance, which can be costly. This is the conundrum we face with respect to finding “the next Zika”: adequate arbovirus surveillance is costly, and the results of the surveillance may be as innocuous as the viruses being surveilled.
Against the inexorably circulation and spread of arboviruses, the discovery and emergence of new arboviruses among naïve population and previously unscathed territories, we have ultimately to be prepared and arbovirology must persists in the in the concert of medical sciences.
2. Vasilakis N, Tesh RB, Popov VL, Widen SG, Wood TG, Forrester NL, Gonzalez JP, Saluzzo JF, Alkhovsky S, Lam SK, Mackenzie JS. Exploiting the Legacy of the Arbovirus Hunters. Viruses. 2019 May;11(5):471.
3. Chen W, Qiu F, Calisher CH, Liu J, Chen H, Li X, Zhao Z, Chen Y, Kuang J, Wang M. Twenty-eight alphavirus strains isolated from mosquitoes and ticks captured from Hainan Island, China. Zhonghua shi yan he lin chuang bing du xue za zhi= Zhonghua shiyan he linchuang bingduxue zazhi=Chinese journal of experimental and clinical virology. 1997 Jun;11(2):144-6.
4. Meng WS, Zhang JB, Sun XH, Liu QN, Chen Z, Zhai YG, Fu SH, Cao YX, Wang HY, Ding J, Chu FJ. Isolation and identification of arboviruses from mosquito pools in some regions of Liaoning province, China. Zhonghua liu xing bing xue za zhi=Zhonghua liuxingbingxue zazhi. 2009 Jan;30(1):50-4.
5. Kraemer MU, Reiner RC, Brady OJ, Messina JP, Gilbert M, Pigott DM, Yi D, Johnson K, Earl L, Marczak LB, Shirude S. Past and future spread of the arbovirus vectors Aedes aegypti and Aedes albopictus. Nature microbiology. 2019 May;4(5):854.