Page 40 - ICGES Libro de Resúmenes MAC

Resumen de Conferencias Internacionales (CI)

ALPHAVIRUSES: EMERGENCE, PATHOGENESIS, AND
CI­05 VACCINATION

Scott C. Weaver

Institute for Human Infections and Immunity, World Reference Center for
Emerging Viruses and Arboviruses, and Department of Microbiology &
Immunology, University of Texas Medical Branch, Galveston, USA

Alphaviruses are important pathogens of both people and economically
important livestock nearly throughout the Americas. Venezuelan equine
encephalitis (VEE) and related VEE complex viruses cause endemic disease
affecting an estimated 10,000 persons annually in Latin America when spillover
from sylvatic, rodent­amplified cycles occurs. Most VEE is misdiagnosed as
dengue but a small proportion of cases progress to neurologic disease that can
be fatal. Equine­amplified epizootics occur periodically, leading to hundreds­of­
thousands of equine and human spillover cases. The last major epizootic
occurred in 1995 in northern South America, so another may be overdue.
Eastern equine encephalitis [Madariaga virus (MADV) in Latin America] causes
smaller equine and human outbreaks in North America, but with high case­
fatality rates. In Latin America, MADV infection has long been associated with
equine encephalitis but only recently in Panama have human outbreaks of
encephalitis been recognized. Western equine encephalitis virus (WEEV)
circulates throughout the Americas with equine and human outbreaks observed
mainly in temperate regions. In North America WEEV cases have nearly
disappeared since the mid­20th century, probably due to ecologic changes
affecting avian hosts and Culex spp. vectors along with equine vaccination.
Among alphaviruses that cause a rash­arthralgia human syndrome, Mayaro
(MAYV) circulates in South America and possibly Panama among nonhuman
primates in sylvatic cycles. Spillover infections of humans are common and
viremia levels combined with vectorial capacity data suggest the possibility of
human­amplified, urban transmission. The recent identification of a human case
in Haiti suggests MAYV expansion into the Caribbean. Recently, chikungunya
virus (CHIKV) arrived in the Americas from Asia and Africa to cause major
epidemics of severe, debilitating and often chronic throughout the tropics.
Although some CHIKV strains have adapted for efficient transmission by Aedes
albopictus, these two American strains have epistatic constraints that are
predicted to confine them mainly to A. aegypti transmission. Emergence
mechanisms for all of these alphaviruses will be discussed, along with the state
of vaccine development, and scientific, regulatory and economic challenges to
licensure.

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