Zika virus (ZIKV) was ﬁrst isolated from a nonhuman primate in Uganda in 1947 and from Ae. africanus mosquitoes in 1948. Human infections with ZIKV were sporadic for half a century before emerging in the Paciﬁc and the Americas. The ﬁrst reported outbreak of Zika fever occurred on the Western Paciﬁc island of Yap in the Federated States of Micronesia in 2007.
This was followed by a larger epidemic in French Polynesia in the South Paciﬁc in 2013 and 2014, with an estimated 30,000 symptomatic infections. ZIKV infection was associated with only mild illness prior to the large French Polynesian outbreak in 2013–2014 when severe neurological complications were reported.
In early 2015, ZIKV emerged for the ﬁrst time in the Americas (in Brazil) and, by the end of the year, local transmission of ZIKV had been reported in more than 20 countries in the Caribbean and South, Central, and North America. With the emergence of ZIKV in Brazil came a dramatic increase in the number of the babies born with microcephaly, a rare disorder in which a baby’s head is much smaller than normal. By late December 2015, the estimated number of suspected cases of ZIKV infection ranged from 440,000 to 1,300,000.
Zika is normally maintained in a human/primate-mosquito cycle. The mosquito vectors are primarily in the genus Aedes (Ae. aegypti and Ae. albopictus). With the emergence of Zika as a major vector-borne disease has come the discovery that the virus can also be transmitted sexually and through blood transfusions.
In 2016, over 5,100 cases of Zika virus infection were reported in the United states including 285 cases in Florida and six cases in Texas that were acquired through presumed local mosquito-borne transmission. Cases were reported from all states except Alaska. There is a high potential for ZIKV emergence in U.S. urban centers that are infested with competent mosquito vectors such as Ae. aegypti and Ae. albopictus.
Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito. These are the same mosquitoes that spread dengue and chikungunya viruses. The yellow fever mosquito, Aedes aegypti, is found in tropical and subtropical regions throughout the world and has experienced a resurgence into many areas where it was previously eliminated including parts of the United States and even the European periphery. The Asian tiger mosquito, Aedes albopictus, is also a capable vector and has spread from its Asian origin to five continents during the last three decades. It has now been detected in at least 38 countries and has become established in 28. Both species are aggressive daytime biters and live in close association with human habitations.
Symptoms of Zika
The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week. Only about one in five people who are infected actually become sick, and for most people the infection causes no symptoms and leads to no lasting harm. Mosquitoes become infected when they feed on a person already infected with the virus. Scientific concern is currently focused on the possible association of birth defects (microcephaly) to women who become infected while pregnant. Additionally, there are reports of a temporary form of paralysis (Guillain Barre´ syndrome) that has been reported following exposure to the Zika virus.
How to fight against Zika
Reducing Zika virus infections is completely dependent on the control of mosquito vectors by eliminating larval habitat or applying pesticides and limiting person-mosquito contact through the use of repellents and improvements to housing (screening). Mosquito surveillance is a key component of any local integrated vector management program. The goal of mosquito-based surveillance is to quantify human risk by determining the presence and abundance of local vector populations. Biogents mosquito traps such as the BG-Sentinel are very effective in monitoring populations of Ae. aegypti and Ae. albopictus in a local area. For further information on controlling vectors of Zika virus see the CDC publication: Surveillance and Control of Aedes aegypti and Aedes albopictus >
Mosquito surveillance practices such as the number and type of traps used and the frequency of sampling depend largely on available funding, resources, and trained staff. However, in order to quickly identify and mitigate a mosquito-borne disease outbreak, establishing and maintaining a local vector surveillance program is critical.