Emerging and re-emerging viruses: A global challenge illustrated by Chikungunya virus outbreaks

Abstract

In recent decades, the issue of emerging and re-emerging infectious diseases, especially those related to viruses, has become an increasingly important area of concern in public health. It is of significance to anticipate future epidemics by accumulating knowledge through appropriate research and by monitoring their emergence using indicators from different sources. The objective is to alert and respond effectively in order to reduce the adverse impact on the general populations. Most of the emerging pathogens in humans originate from known zoonosis. These pathogens have been engaged in long-standing and highly successful interactions with their hosts since their origins are exquisitely adapted to host parasitism. They developed strategies aimed at: (1) maximizing invasion rate; (2) selecting host traits that can reduce their impact on host life span and fertility; (3) ensuring timely replication and survival both within host and between hosts; and (4) facilitating reliable transmission to progeny. In this context, Arboviruses (or ARthropod-BOrne viruses), will represent with certainty a threat for the coming century. The unprecedented epidemic of Chikungunya virus which occurred between 2005 and 2006 in the French Reunion Island in the Indian Ocean, followed by several outbreaks in other parts of the world, such as India and Southern Europe, has attracted the attention of medical and state authorities about the risks linked to this re-emerging mosquito-borne virus. This is an excellent model to illustrate the issues we are facing today and to improve how to respond tomorrow.

Keywords: Arbovirus; Biosurveillance; Chikungunya virus; Ecosystems; Emerging virus; Health threats.

Figure 1

Major emerging and re-emerging virus-associated diseases in human. The etiological agents of infectious diseases identified since 1973, as newly discovered viruses of public health importance. It includes a few arboviruses that are transmitted to humans by arthropod vectors, upon biting. Among known arboviruses, some are transmitted by mosquitoes (Bunyaviridae: La Crosse encephalitis, California encephalitis, Rift Valley fever; Flaviviridae: Dengue fever, Yellow fever, Japanese encephalitis, West Nile; Togaviridae: Eastern equine encephalomyelitis, Western equine encephalomyelitis, Venezuelan equine encephalomyelitis; Ross River fever, O’Nyong-nyong fever, Chikungunya), others by ticks (Bunyaviridae: Crimean-Congo hemorrhagic fever; Flaviviridae: Tick-borne encephalitis; Omsk hemorrhagic fever; Reoviridae: Colorado tick fever). Most of the emerging pathogens in humans originate from zoonosis.

Figure 2

Examples of large arbovirus outbreaks, from the literature. This diagram illustrates several unexpected arbovirus outbreaks that have occurred in regions of the world which are currently the most vulnerable to arboviruses. It is likely that in the coming years other parts of the world will be affected, including regions that are outside of the tropical area.

Figure 3

Globalization of the distribution of pathogens. Climate change, ecosystems evolution, anarchic urbanization, human behaviors, migration of humans and animals, development of air transport, extensive agriculture and water control projects, contribute to rapid spread of vectors and arbovirus-induced diseases in the world.

Figure 4

Accumulation of knowledge. We know relatively little about the cycle of CHIKV replication in mammalian cells and insect cells. It remains necessary to conduct experimental work to better understand the virus replication cycle, particularly in order to develop therapeutic agents. Understanding of each stage of the cycle, the molecular crosstalk between the pathogen and the host, and each molecular interaction, may offer a new avenue to fight the pathogen.

Figure 5

Emerging arbovirus diseases and the biosurveillance. Biosurveillance is based on three main principles: research (accumulation of knowledge in all fields of science), large scale monitoring for early warning and intervention to prevent or reduce the epidemic risks.