Aedes albopictus and the crisis of co-circulating arboviruses in the Pacific

“ Abstract Since the beginning of this century, humanity has been facing a new emerging, or re-emerging, virus threat almost every year: West Nile, Influenza A, avian flu, dengue, Chikungunya, SARS, MERS, Ebola, and now Zika, the latest newcomer. Zika virus (ZIKV) , a flavivirus transmitted by Aedes mosquitoes, was identified in 1947 in a sentinel monkey in Uganda, and later on in humans in Nigeria. ”

“ The recent striking emergence of cases of Zika in Latin America poses a threat for a worldwide outbreak of this mosquito-borne viral infection. The globalisation of the human population promotes the movement of asymptomatic carriers between countries in the same or different continents. Pregnant women are considered a high-risk group for Zika, as infection is strongly associated with, if as yet unproven as a cause of, microcephaly in the developing foetus. ”

“ Zika virus, an Aedes mosquito-borne flavivirus, is fast becoming a worldwide public health concern following its suspected association with over 4000 recent cases of microcephaly among newborn infants in Brazil.
Discussion
Prior to its emergence in Latin America in 2015–2016, Zika was known to exist at a relatively low prevalence in parts of Africa, Asia and the Pacific islands. An extension of its apparent global dispersion may be enabled by climate conditions suitable to support the population growth of A. aegypti and A. albopictus mosquitoes over an expanding geographical range. ”

“ In addition, increased globalisation continues to pose a risk for the spread of infection. Further, suspicions of alternative modes of virus transmission (sexual and vertical) , if proven, provide a platform for outbreaks in mosquito non-endemic regions as well. Since a vaccine or anti-viral therapy is not yet available, current means of disease prevention involve protection from mosquito bites, excluding pregnant females from travelling to Zika-endemic territories, and practicing safe sex in those countries. ”

“ Aedes (Stegomyia) albopictus (Skuse, 1895) is nowadays the most notorious invasive Culicidae. From its native range in Asia, the species has spread throughout the Americas, Europe and Africa, mainly via international trade in used tires [1] . Its capacity to transmit a large number of arboviruses is well documented. Although less efficient than Aedes aegypti for the dengue viruses transmission, it was responsible for large dengue epidemics in Japan in 1942–1945 [2] , for the DEN-1 outbreak in Hawaii in 2001 [3] and for the DEN-2 outbreaks in La Reunion in 1977–78 and 2004 [4] , [5] . ”

“ Itching or itching rash has been suggested to be added to the case definition issued by the Pan American Health Organization (PAHO) .
Introduction Background
Since 2015, Brazil is faced with the challenge of three co-circulating arboviruses of major public health importance. For the last 30 years, dengue virus (DENV) infection has been the main mosquito-transmitted threat in the country, which has suffered several epidemics caused by all four serotypes, [1] , [2] fostered by the widespread presence of its main vector, Aedes aegypti, in densely populated urban areas. ”

“ The introduction and establishment of Ae. albopictus in Tonga was expected due to the geographical proximity of this country to Fiji where the species is strongly established. The pathway of introduction is unknown. The expansion of Ae. albopictus in the Pacific region poses an increasing threat to public health given the role this mosquito plays as primary vector of emerging infectious diseases such as Chikungunya fever. ”

“ The ratio of Aedes albopictus pools positive for ZIKV was similar to that positive for dengue virus during the concomitant dengue outbreak suggesting similar mosquito infection rates and, presumably, underlying a human ZIKV outbreak. ZIKV sequences from the envelope and NS3 genes were amplified from a human serum sample. Phylogenetic analysis placed the Gabonese ZIKV at a basal position in the African lineage, pointing to ancestral genetic diversification and spread. ”

“ Patients develop a mild dengue-like syndrome, including fever, headache, rash, arthralgia and conjunctivitis. This clinical similarity with other, more commonly diagnosed arboviral infections such as chikungunya (CHIKV) and dengue (DENV) , might delay the diagnosis and/or lead to underestimation of ZIKV infections.
Here, we report the first direct evidence of ZIKV epidemic activity in Central Africa, and its occurrence in an urban environment during concomitant CHIKV/DENV outbreaks in Libreville, the capital of Gabon, in 2007. ”

“ Papua New Guinea, Solomon Islands, Fiji, and the Kingdom of Tonga, where it was first detected in July 2011. It is absent from New Caledonia and French Polynesia where routine entomological surveillance is carried out, and was not detected during entomological work in 2007, either on the Cook Islands or on the Wallis and Futuna Islands. The species was not reported from American Samoa in 2004, but it is mentioned as probably present in Vanuatu. This is the first report of Ae. albopictus in Tonga. ”

“ Clinical Manifestations and Pathogeny Humans Zika virus infection has been reported to be symptomatic only in around 18% of the cases ( [110] ) , in which it causes a mild, self-limiting disease with an incubation period of up to 10 days, often mistaken with other arboviral infections like dengue or chikungunya. Clinical manifestations in symptomatic cases resemble that of an influenza-like syndrome ( [68] ) , being the most common symptoms fever, rash, arthralgia, and conjunctivitis ”

“ Similar stories, illustrative of the sudden incidence of the symptoms, circulate during every epidemic of dengue. Sometimes the fever is ushered in by a feeling of chilliness or even by a smart rigor; sometimes a deep flushing of the face is the first sign of the disease.
However introduced, fever rapidly increases. The head and eyeballs ache excessively, and some limb or joint, or even the whole body, is racked with peculiar stiff, rheumatic-like pains, which, as the patient soon discovers, are very much aggravated by movement. ”

“ Genetic and serologic properties of Zika virus associated with an epidemic, Yap State, Micronesia, 2007. Emerg Infect Dis 14: 1232–1239 pmid:186806461 2 Leroy EM, Nkoghe D, Ollomo B, Nze-Nkogue C, Becquart P, et al. (2009) Concurrent chikungunya and dengue virus infections during simultaneous outbreaks, Gabon, 2007. Emerg Infect Dis 15: 591–593 pmid:193317401 2 3 4 Caron M, Paupy C, Grard G, Becquart P, Mombo I, et al. (2012) Recent introduction and rapid dissemination of Chikungunya virus and Dengue virus serotype 2 associated with human and mosquito coinfections in Gabon, central Africa. ”

“ Our data suggests that in a previously naïve adult population, ZIKV causes a self-limited and mostly benign disease characterized by a pruritic maculopapular rash and absent or low-grade, short-termed fever. ZIKV-like disease was not a notifiable condition in Rio de Janeiro until October 22th, 2015. This partially explains why our data differs from the official figures, [18] as the syndromic surveillance study that was implemented in 2007 (long before the ZIKV outbreak started) is more likely to detect changes in the clinical patterns of dengue compared to the routine health system. ”

“ Pathology.—Yellow fever, dengue and phlebotomus fever have several important points in common, a circumstance suggestive of the possibility of a common or, at all events, a similar origin. Each is transmitted by an insect; their germs occur in the blood-stream and are ultramicroscopic; they are diseases of warm climates only; and, clinically, they are characterized by a short incubation period, a short and rapidly developed fever which is usually associated with relatively slow pulse and leucopenia, with relative decrease of the polynuclears. ”

“ In tropical work we combine the large mononuclears and transitionals in a differential count. They are the phagocytes of animal cells or parasites. The disease in which their increase is best recognized is malaria and an increase to 15% where the blood shows moderate leucopenia is very significant. The melaniferous leucocytes of malaria are cells of this type.
Other protozoal infections, as kala-azar, trypanosomiasis and amoebiasis cause it. Filterable-virus diseases may show a mononuclear increase, thus yellow fever and dengue both give an increase about the fifth or sixth day. ”

“ Some writers state that the gravity of any given case is in direct proportion to the abundance of the eruption; others deny this. In Europeans an attack of dengue very often leads to a condition of debility necessitating temporary change of climate, or even return to Europe. In both Europeans and natives the attendant lowering of the resisting powers predisposes to other and more dangerous diseases, such as malaria, dysentery, phthisis, and so forth; consequently dengue, otherwise a benign disease, may become a source of public danger. ”

“ But, leaving aside its origin, it is authentically known that wherever dengue has appeared it has almost always been in the form of an epidemic, spreading from place to place and from family to family, without respect to race or nationality, to age, occupation or position, until every one susceptible to the disease was affected. Slaughter reports from India that even domestic animals, especially dogs and cats, were not exempt, as they appeared to suffer from rheumatoid affections of the joints. ”

“ As Zika adapts to new niches in the Americas, the roles played by humans and non-human primates, other animals and arthropods as primary and intermediate hosts must be understood. Factors which will influence the rate of spread include availability of vector species, temperature and humidity available to support transmissibility, and high mosquito to human contact rates. Similar to dengue and chikungunya, Aedes sp. (Ae. aegypti and Ae. albopictus) appear to be the leading candidate Zika vectors in the outbreak. Potential involvement of other insect vectors including Culex sp. ”

“ Widely distributed throughout tropical areas of Asia and Africa, ZIKV is transmitted by a broad range of mosquito species, most of which are sylvatic or rural, Aedes aegypti, an anthropophilic and urban species, being considered the main ZIKV epidemic vector. ”

“ This mosquito species being native to South-East Asia, our findings may help to explain human ZIKV transmission in Asia.
Aedes albopictus was first introduced in Africa in 1991 [31] and detected in Gabon in 2007, where its invasion likely contributed to the emergence of CHIKV and DENV in this country [14] – [16] , [32] . Multiple lines of evidence supporting its increasing impact as an arboviral vector have also been obtained during CHIKV outbreaks in the Indian Ocean region (2005–2007) and in Italy (2007) [33] , [34] through viral evolutionary convergence of Ae. ”

“ Chikungunya and dengue viruses emerged in Gabon in 2007, with large outbreaks primarily affecting the capital Libreville and several northern towns. Both viruses subsequently spread to the south-east of the country, with new outbreaks occurring in 2010. The mosquito species Aedes albopictus, that was known as a secondary vector for both viruses, recently invaded the country and was the primary vector involved in the Gabonese outbreaks. We conducted a retrospective study of human sera and mosquitoes collected in Gabon from 2007 to 2010, in order to identify other circulating arboviruses. ”

“ Evidence of human ZIKV infections in Central Africa is limited to one isolate from RCA in 1991 [5] and two serological surveys performed 50 years ago in Gabon [22] , [23] . No report of human ZIKV infections was made in other countries of the Congo basin forest block, despite probable circulation through a sylvan natural cycle. We provide here the first direct evidence of human ZIKV infections in Gabon, as well as its occurrence in an urban transmission cycle, and the probable role of Ae. albopictus as an epidemic vector. ”

“ We found that the Gabonese ZIKV strain belonged to the African lineage, and phylogenetic analysis suggested ancestral diversification and spread rather than recent introduction. These findings, showing for the first time epidemic ZIKV activity in an urban environment in Central Africa and the presence of ZIKV in the invasive mosquito Aedes albopictus, raise the possibility of a new emerging threat to human health. ”

“ In French Polynesia , the species is currently absent. Mosquito sampling is frequently conducted for research or surveillance purposes on several archipelagoes (Society Islands, Tuamotu and Marquesas) . Sampling is mostly done using ovitraps and BG Sentinel® traps. Aedes albopictus has not been detected so far.
On Wallis and Futuna Islands , entomological investigations were carried out by IPNC during a dengue outbreak in 2002 and 2003, and entomological records were updated and extended to the Horne group (Futuna and Alofi islands) in August 2007, supporting that Ae. albopictus was absent. ”

“ These data reveal an unusual natural life cycle for this virus, occurring in an urban environment, and potentially representing a new emerging threat due to this novel association with a highly invasive vector whose geographic range is still expanding across the globe.==Abstract== Author SummaryNot previously considered an important human arboviral pathogen, the epidemic capacity of Zika virus (ZIKV, a dengue-related flavivirus) was revealed by the Micronesia outbreak in 2007, which affected about 5000 persons. ”

“ While it is possible that the distribution of Zika in the Asia Pacific region could eventually reach as far as Australia, it should be containable in this and other developed countries where Aedes spp. mosquitoes are found through adherence to current measures of mosquito control. Such vector control programs are in place to combat dengue, yellow fever and Japanese encephalitis. It is highly likely that any outbreak initiated by an infected index case returning from overseas would be locally restricted, just like current dengue outbreaks that occur sporadically in northern Queensland [34] . ”

“ In addition to the spread of Zika via mosquito bite, the current news media is awash with stories regarding the possibilities of sexual, blood-borne and vertical transmission of ZIKV. In a scenario in which one or more of these routes proves to be a potential mode of transmission, paradoxically the effect may be to facilitate any outbreak of Zika in those areas regardless of Aedes mosquito availability. This would pose a serious threat for the global spread of ZIKV and thus constitutes a major public health problem. ”