Arboviruses (or arthropod-borne viruses) are a heterogeneous group of viruses that share the same usual route of entry into humans: via the bite of an infected mosquito, tick, sandfly, or other arthropod. The life cycle of most arboviruses is characterized by the ability of the virus to replicate in both an arthropod vector and a vertebrate “natural” host (usually birds or small mammals) and by transmission between these 2 organisms at the time of the arthropod’s bite (Fig. 300-1). This cycle leads to establishment or maintenance of the virus in a given ecosystem. Humans or domestic animals are only “incidental” hosts for many species of arboviruses, as infection in such hosts (although capable of causing disease) is often a dead end for the virus due to viremia being too low or too transient to contribute to maintenance of the cycle of transmission. Some viruses are specific to a single genus or species of insect, while others are transmissible by multiple vectors. In addition, some arthropods are capable of transovarial transmission, wherein their eggs (which sometimes overwinter and hatch in spring) are infected with the virus, allowing viral maintenance in areas of colder climate.
Ecosystem changes, both natural and anthropogenic, can affect the complex ecology of arboviruses, alter transmission patterns, and drive the emergence and resurgence of diseases in new regions. A global resurgence of several arboviruses has occurred in the last 40 years, most notably of West Nile virus (WNV), dengue viruses (DENV), chikungunya virus (CHIKV), and Zika virus (ZIKV). Their geographic expansion has been associated with a number of factors such as climate change, expansion of mosquito vector distributions, human population growth and urbanization, and increasing international travel. In particular, the invasion of Aedes albopictus mosquitoes into the Americas, Europe, and Africa has driven large-scale epidemics of DENV and CHIKV in these regions. ZIKV has followed the path of DENV and CHIKV emergence in the Americas, spreading to countries with competent vector species including Aedes aegypti. Ongoing global change is anticipated to drive further arbovirus emergence, underscoring the current and future importance of this group of viruses.
Arboviruses generally produce 1 of 4 clinical syndromes: (1) central nervous system (CNS) disease, (2) febrile illness with rash, (3) febrile illness with arthropathy, or (4) hemorrhagic fever syndrome. In North America, encephalitis is the most important manifestation of arboviral infection, with several viruses producing sporadic disease as well as outbreaks of infection each year. Table 300-1 provides a list of arboviruses presenting with different symptom complexes and details the vector, reservoir, distribution, incubation period, and population most affected.
TABLE 300-1ARBOVIRUSES ...