[Dengue, Zika and Chikungunya]

Arboviruses are transmitted by arthropods, including those responsible for the current pandemic: alphavirus (Chikungunya) and flaviviruses (dengue and Zika). Its importance increased in the Americas over the past 20 years. The main vectors are Aedes aegypti and A. albopictus. Dengue infection provides long lasting immunity against the specific serotype and temporary to the other three. Subsequent infection by another serotype determines more serious disease. There is a registered vaccine for dengue, Dengvaxia (Sanofi Pasteur). Other two (Butantan and Takeda) are in Phase III in 2016. Zika infection is usually asymptomatic or occurs with rash, conjunctivitis and not very high fever. There is no vaccine or specific treatment. It can be transmitted by parental, sexual and via blood transfusion. It has been associated with microcephaly. Chikungunya causes prolonged joint pain and persistent immune response. Two candidate vaccines are in Phase II. Dengue direct diagnosis is performed by virus isolation, RT-PCR and ELISA for NS1 antigen detection; indirect methods are ELISA-IgM (cross-reacting with other flavivirus), MAC-ELISA, and plaque neutralization. Zika is diagnosed by RT-PCR and virus isolation. Serological diagnosis cross-reacts with other flavivirus. For CHIKV culture, RT-PCR, MAC-ELISA and plaque neutralization are used. Against Aedes organophosphate larvicides (temephos), organophosphorus insecticides (malathion and fenitrothion) and pyrethroids (permethrin and deltamethrin) are usually employed. Resistance has been described to all these products. Vegetable derivatives are less expensive and biodegradable, including citronella oil, which microencapsulated can be preserved from evaporation.

Risk and Control of Mosquito-Borne Diseases in Southeast Asian Rubber Plantations

Unprecedented economic growth in Southeast Asia (SEA) has encouraged the expansion of rubber plantations. This land-use transformation is changing the risk of mosquito-borne diseases. Mature plantations provide ideal habitats for the mosquito vectors of malaria, dengue, and chikungunya. Migrant workers may introduce pathogens into plantation areas, most worryingly artemisinin-resistant malaria parasites. The close proximity of rubber plantations to natural forest also increases the threat from zoonoses, where new vector-borne pathogens spill over from wild animals into humans. There is therefore an urgent need to scale up vector control and access to health care for rubber workers. This requires an intersectoral approach with strong collaboration between the health sector, rubber industry, and local communities.

[A model for evaluation of key measures for control of chikungunya fever outbreak in China]

OBJECTIVE

To analyze the transmission pattern of Chikungunya (CHIK) fever in community and evaluate the effectiveness of mosquito control, case isolation and other key control measures by using ordinary differential equation (ODE) model.

METHODS

According to natural history of CHIK, an ODE model for the epidemiological analysis of CHIK outbreak was established. The key parameters of the model were obtained by fitting the model with reported outbreak data of the first CHIK outbreak in China. Then the outbreak characteristics without intervention, the effectiveness of mosquito control and case isolation were simulated.

RESULTS

Without intervention, an imported case would cause an outbreak in a community with population of 11 000, and cumulative case number would exceed 941 when the total attack rate was 8.55%. The results of our simulation revealed that the effectiveness of case isolation was not perfect enough when it was implemented alone. Although the number of cases could be decreased by case isolation, the duration of outbreak would not be shortened. Differently, the effectiveness of mosquito control was remarkable. In addition, the earlier the measure was implemented, the better the effectiveness would be. The effectiveness of mosquito control plus case isolation was same with mosquito control.

CONCLUSION

To control a CHIK outbreak, mosquito control is the most recommended measures. However, case isolation is also necessary as the supplementation of mosquito control.

Extended Preclinical Safety, Efficacy and Stability Testing of a Live-attenuated Chikungunya Vaccine Candidate

We recently described a new, live-attenuated vaccine candidate for chikungunya (CHIK) fever, CHIKV/IRES. This vaccine was shown to be well attenuated, immunogenic and efficacious in protecting against CHIK virus (CHIKV) challenge of mice and nonhuman primates. To further evaluate its preclinical safety, we compared CHIKV/IRES distribution and viral loads in interferon-α/β receptor-incompetent A129 mice to another CHIK vaccine candidate, 181/clone25, which proved highly immunogenic but mildly reactive in human Phase I/II clinical trials. Compared to wild-type CHIK virus, (wt-CHIKV), both vaccines generated lower viral loads in a wide variety of tissues and organs, including the brain and leg muscle, but CHIKV/IRES exhibited marked restrictions in dissemination and viral loads compared to 181/clone25, and was never found outside the blood, spleen and muscle. Unlike wt-CHIKV, which caused disrupted splenic architecture and hepatic lesions, histopathological lesions were not observed in animals infected with either vaccine strain. To examine the stability of attenuation, both vaccines were passaged 5 times intracranially in infant A129 mice, then assessed for changes in virulence by comparing parental and passaged viruses for footpad swelling, weight stability and survival after subcutaneous infection. Whereas strain 181/clone25 p5 underwent a significant increase in virulence as measured by weight loss (from <10% to >30%) and mortality (from 0 to 100%), CHIKV/IRES underwent no detectible change in any measure of virulence (no significant weight loss and no mortality). These data indicate greater nonclinical safety of the CHIKV/IRES vaccine candidate compared to 181/clone25, further supporting its eligibility for human testing.

Chikungunya fever is a reemerging, mosquito-borne viral disease that causes severe, debilitating, and often chronic arthralgia. The virus reemerged from Africa in 2004 and has since caused disease in millions of persons, including in over one million in the Americas since it arrived for the first time in modern scientific history in late 2013. An effective vaccine is critically needed to protect against this medically and economically devastating disease as well as to interrupt the human-mosquito transmission cycle. To further test a new, live-attenuated vaccine candidate for chikungunya fever, we conducted extensive preclinical safety evaluations using another vaccine candidate tested in humans, 181/clone 25, as a benchmark. The new vaccine candidate, CHIKV/IRES, replicated to lower levels in a mouse model and generated lesser signs of disease. Furthermore, it was more stably attenuated following mouse passages. These results support the further development of the new CHIKV/IRES vaccine candidate toward clinical testing in humans.

Control of Aedes aegypti and Ae. albopictus, the vectors of dengue and chikungunya, by using pheromone C21 with an insect growth regulator: Results of multicentric trials from 2007-12 in India

BACKGROUND & OBJECTIVES

Aedes mosquito control has gained much importance nowadays in view of rise in number of reported cases of dengue and chikungunya in India and other countries. In the present study, C21 attracticide (containing a pheromone and an insect growth regulator—IGR, developed by Defence Research and Development Establishment (DRDE), Gwalior, India was tested for its feasibility for surveillance and control of Aedes mosquito in a multicentric mode from October 2007 to June 2012 in urban (Delhi, and Bengaluru district, Karnataka) and suburban (Alappuzha district, Kerala) settings of the country in three phases.

METHODS

Across the randomly selected households in each study area, two to four containers treated with attracticide (experimental) and untreated (control) were placed and monitored by trained surveillance workers on weekly/ fortnightly basis for determining the presence of eggs, larvae and pupae. Container positivity, percent larvae, egg and pupae collected were determined during different phases and analyzed statistically using SPSS 18.0.

RESULTS

Container positivity was found statistically significant at Bengaluru and Alappuzha, Kerala while in Delhi, it was found non-significant. Eggs collected from experimental containers were significantly higher in comparison to control at all the locations except Delhi. Also larvae collected from control containers were significantly higher at all the locations except Bengaluru. Pupae collected from control containers remained significantly higher at all the locations as no pupal formation was recorded from experimental containers.

INTERPRETATION & CONCLUSION

The use of C21 attracticide hampered pupal formation, thus inhibiting adult population in the study areas. The study established that C21 attracticide was efficacious in the field conditions and has potential for use in surveillance and management of dengue and chikungunya mosquitoes.

Autochthonous Chikungunya Transmission and Extreme Climate Events in Southern France

Background

Extreme precipitation events are increasing as a result of ongoing global warming, but controversy surrounds the relationship between flooding and mosquito-borne diseases. A common view among the scientific community and public health officers is that heavy rainfalls have a flushing effect on breeding sites, which negatively affects vector populations, thereby diminishing disease transmission. During 2014 in Montpellier, France, there were at least 11 autochthonous cases of chikungunya caused by the invasive tiger mosquito Aedes albopictus in the vicinity of an imported case. We show that an extreme rainfall event increased and extended the abundance of the disease vector Ae. albopictus, hence the period of autochthonous transmission of chikungunya.

Methodology/Principal Findings

We report results from close monitoring of the adult and egg population of the chikungunya vector Ae. albopictus through weekly sampling over the entire mosquito breeding season, which revealed an unexpected pattern. Statistical analysis of the seasonal dynamics of female abundance in relation to climatic factors showed that these relationships changed after the heavy rainfall event. Before the inundations, accumulated temperatures are the most important variable predicting Ae. albopictus seasonal dynamics. However, after the inundations, accumulated rainfall over the 4 weeks prior to capture predicts the seasonal dynamics of this species and extension of the transmission period.

Conclusions/Significance

Our empirical data suggests that heavy rainfall events did increase the risk of arbovirus transmission in Southern France in 2014 by favouring a rapid rise in abundance of vector mosquitoes. Further studies should now confirm these results in different ecological contexts, so that the impact of global change and extreme climatic events on mosquito population dynamics and the risk of disease transmission can be adequately understood.

During last years, we have seen an astonishing expansion of Chikungunya virus and an increase in dengue cases worldwide, together with the worldwide expansion of the Asian tiger mosquito Aedes albopictus. In addition, extreme rainfall events are envisaged to become increasingly likely as a result of ongoing climate change, but controversy surrounds the relationship between extreme rainfall events and mosquito-borne diseases. The common view in most works on climate and mosquito-borne diseases is that heavy rainfalls produce a flushing effect of immature mosquitoes in breeding containers, diminishing the mosquito abundance and in turn diminishing disease transmission. We analysed the relationships between the autochthonous chikungunya transmission in Montpellier (Southern France) in 2014, an extreme rainfall event that flooded the city, and a close monitoring of the vector Ae. albopictus, revealing an unexpected pattern. This extreme rainfall event did not, in fact, decrease but instead had increased the global risk of chikungunya transmission by sustaining high abundance of the disease vector Ae. albopictus, hence extending the transmission period. We propose that an effort on source reduction campaigns must be implemented after heavy rainfall events. These results are relevant to those involved in the surveillance and control of chikungunya and dengue transmission in temperate as well as tropical areas.

Do we need a vaccine against chikungunya?

During the last decade, the chikungunya (CHIKV) virus has expanded its range of activity, conquering new territories and becoming an important global health threat. In particular, the challenge represented by the recent emergence of CHIKV in the Americas has strengthened the need of a safe and effective vaccine. Although research on vaccines against CHIKV has been slow, a few vaccine candidates have been tested over the years. Inactivated and attenuated vaccine candidates have shown promising results in phase I/II trials, and engineered vaccines have proven to be safe and immunogenic in mouse and/or non-human primate models. Recently, a vaccine based on virus-like particles (VLP) has been successfully tested in a phase I trial. However, large phase I/II controlled trials, which are needed in order to provide evidence of vaccine efficacy, may be planned only under certain conditions. First, they should be conducted during epidemic periods, when a large number of cases occur, in order to ensure an adequate study power. Second, they are expensive and investments returns are not always guaranteed. To overcome this problem, public/private partnership and government support, the identification of target population groups for vaccination and the commitment of donor agencies are key factors for supporting both the development and the availability of vaccines against neglected tropical diseases like chikungunya.

[Reemergence of Chikungunya virus]

Arboviral diseases transmitted by mosquitoes such as Dengue, Chikungunya and West Nile are global health issues of growing magnitude. Their dissemination in new areas is triggered by increased mobility of persons, animal reservoirs and vectors. This article describes virological, epidemiological and clinical aspects of Chikungunya, which causes sporadic cases or epidemics, sometimes massive, such as the one spreading in the Americas since December 2013. Chikungunya should be suspected in all travellers presenting with fever, arthralgia and sometimes a rash returning from an endemic area. In the absence of vaccine, individual protection relies on the prevention of mosquito bites.

Status of DDT and pyrethroid resistance in Indian Aedes albopictus and absence of knockdown resistance (kdr) mutation

BACKGROUND & OBJECTIVES

Aedes albopictus is one of the vectors for dengue and chikungunya and emergence of pyrethroid resistance in this species could be of a major concern in controlling the vector. This study reports insecticide susceptibility status of Ae. albopictus to DDT and pyrethroids in some Indian populations and status of presence of knockdown resistance (kdr) mutations.

METHODS

Three to four day old adult female Ae. albopictus collected from Delhi, Gurgaon (Haryana), Hardwar (Uttarakhand), Guwahati (Assam) and Kottayam (Kerala) were bio-assayed with DDT (4%), permethrin (0.75%) and deltamethrin (0.05%) impregnated papers using WHO standard susceptibility test kit. Mosquitoes were PCRgenotyped for F1534C kdr-mutation in the voltage-gated sodium channel (VGSC) gene. DDT and pyrethroid resistant individuals were sequenced for partial domain II, III and IV of VGSC targeting residues S989, I1011, V1016, F1534 and D1794 where kdr mutations are reported in Ae. aegypti.

RESULTS

Adult bioassays revealed varying degree of resistance against DDT among five populations of Ae. albopictus with corrected mortalities ranging between 61 and 92%. Kerala and Delhi populations showed incipient resistance against permethrin and deltamethrin respectively. All other populations were susceptible for both the synthetic pyrethroids. None of the kdr mutations was detected in any of DDT, deltamethrin and permethrin resistant individuals.

INTERPRETATION & CONCLUSION

Ae. albopictus has developed resistance against DDT and there is emergence of incipient resistance against pyrethroids in some populations. So far, there is no evidence of presence of knockdown resistance (kdr) mutation in Ae. albopictus.

Screening of some weeds for larvicidal activity against Aedes albopictus, a vector of dengue and chikungunya

BACKGROUND & OBJECTIVES

Screening of crude extracts of plants facilitates the establishment of highly effective extract for mosquito control. This practice should be preferred before in depth study of plant extracts rather than spending much efforts and energy in detailed examinations for practically ineffective extracts. In this study, leaf powders of four weed plants were used for the quick screening of effective plant extract as larvicide against III instar larvae of Aedes albopictus Skuse. At the same time, effect of different seasons on the larvicidal efficacy of plants and selection of proper solvents for further investigation were also studied.

METHODS

Leaves of Vernonia cinerea, Prosopis juliflora, Hyptis suaveolens and Malvastrum coromandelianum plants were collected in summer, winter and rainy seasons from Madhya Pradesh region (India). To assess the larvicidal efficacy the suspensions of leaf powders in different solvents (isopropanol, methanol, acetone, dimethylsulfoxide and water) were used for larvicidal bioassay. The mortality counts were made after 24 h and the LC50 and LC90 values were calculated.

RESULTS

Results showed that leaf powder of V. cinerea in acetone collected during summer showed highest efficacy with LC50 value of 0.22 g/l and LC90 of 0.96 g/l followed by methanolic solution of P. juliflora with LC50 of 0.44 g/l and LC90 value as 1.85 g/l. Amongst all solvents, leaf powder in acetone; while among seasons, summer collected plant materials were found to be more effective larvicides as compared to others.

INTERPRETATION & CONCLUSION

Summer and winter collected leaves of V. cinerea and P. juliflora dissolved in the solvents of medium polarity range showed significant larval toxicity and thus suggests a detailed study on these plants as potential larval control agents.

[Situational panorama of Mexico against the chikungunya virus pandemic]

Recent outbreaks of emerging diseases emphasize the vulnerability of health systems, as is the case of chikungunya fever. The wide geographical incidence of the virus in the last years requires alerting systems for the prevention, diagnosis, control and eradication of the disease. Given the ecological, epidemiological and socio-economic characteristic of Mexico, this disease affects directly or indirectly the health of the population and development of agricultural, livestock, industrial, fishing, oil and tourism activities in the country. Due to this situation it is essential to make a brief analysis on the main clinical data, epidemiological and preventive measures with which our country counts with to confront the situation.

[Dengue and chikungunya acquired during travel in the tropics]

The global incidence of dengue and chikungunya has greatly increased over recent decades, partly due to the increase of geographic distribution of both vectors. These infections are endemic to the tropics and subtropics, however autochthonous transmission and outbreaks have been described in non-endemic areas. Currently, there is a large chikungunya outbreak in the western hemisphere which started in the Caribbean. Chikungunya had not previously been endemic to this region. Both arboviral infections are important causes of fever in Dutch travellers returning from tropical destinations. The clinical presentations of dengue and chikungunya overlap; both are characterised by high fever and arthralgia. Bleeding and plasma leakage are potentially life-threatening complications of dengue, while persistent arthralgia typifies chikungunya. The prevention of mosquito bites, by using protective clothing and insect repellents, is the only way to prevent infection. No vaccine is yet available.

[Lessons learned in the control of Aedes aegypti to address dengue and the emergency of chikungunya in Iquitos, Peru]

Dengue has affected Iquitos since 1990 causing outbreaks of major impact on public health and for this reason great efforts have been made for its temporal control. Currently, with the expansion of the chikungunya virus in the Americas and the threat of the emergence of the virus in Iquitos, we reflect on lessons learned by way of the activities undertaken in the area of vector control; epidemiological surveillance, diagnosis and clinical management during periods of outbreaks of dengue, in a way that will allow us to better face the threat of an outbreak of chikungunya virus in the largest city in the Peruvian Amazon.

Recombinant modified vaccinia virus Ankara expressing glycoprotein E2 of Chikungunya virus protects AG129 mice against lethal challenge

Chikungunya virus (CHIKV) infection is characterized by rash, acute high fever, chills, headache, nausea, photophobia, vomiting, and severe polyarthralgia. There is evidence that arthralgia can persist for years and result in long-term discomfort. Neurologic disease with fatal outcome has been documented, although at low incidences. The CHIKV RNA genome encodes five structural proteins (C, E1, E2, E3 and 6K). The E1 spike protein drives the fusion process within the cytoplasm, while the E2 protein is believed to interact with cellular receptors and therefore most probably constitutes the target of neutralizing antibodies. We have constructed recombinant Modified Vaccinia Ankara (MVA) expressing E3E2, 6KE1, or the entire CHIKV envelope polyprotein cassette E3E26KE1. MVA is an appropriate platform because of its demonstrated clinical safety and its suitability for expression of various heterologous proteins. After completing the immunization scheme, animals were challenged with CHIV-S27. Immunization of AG129 mice with MVAs expressing E2 or E3E26KE1 elicited neutralizing antibodies in all animals and provided 100% protection against lethal disease. In contrast, 75% of the animals immunized with 6KE1 were protected against lethal infection. In conclusion, MVA expressing the glycoprotein E2 of CHIKV represents as an immunogenic and effective candidate vaccine against CHIKV infections.

Updating the geographical distribution and frequency of Aedes albopictus in Brazil with remarks regarding its range in the Americas

The geographical distribution of Aedes albopictus in Brazil was updated according to the data recorded across the country over the last eight years. Countrywide house indexes (HI) for Ae. albopictus in urban and suburban areas were described for the first time using a sample of Brazilian municipalities. This mosquito is currently present in at least 59% of the Brazilian municipalities and in 24 of the 27 federal units (i.e., 26 states and the Federal District). In 34 Brazilian municipalities, the HI values for Ae. albopictus were higher than those recorded for Ae. aegypti, reaching figures as high as HI = 7.72 in the Southeast Region. Remarks regarding the current range of this mosquito species in the Americas are also presented. Nineteen American countries are currently infested and few mainland American countries have not confirmed the occurrence of Ae. albopictus. The large distribution and high frequency of Ae. albopictus in the Americas may become a critical factor in the spread of arboviruses like chikungunya in the new world.

A novel MVA vectored Chikungunya virus vaccine elicits protective immunity in mice

Background

Chikungunya virus (CHIKV) is a re-emerging arbovirus associated with febrile illness often accompanied by rash and arthralgia that may persist for several years. Outbreaks are associated with high morbidity and create a public health challenge for countries affected. Recent outbreaks have occurred in both Europe and the Americas, suggesting CHIKV may continue to spread. Despite the sustained threat of the virus, there is no approved vaccine or antiviral therapy against CHIKV. Therefore, it is critical to develop a vaccine that is both well tolerated and highly protective.

Methodology/Principal Findings

In this study, we describe the construction and characterization of a modified Vaccinia virus Ankara (MVA) virus expressing CHIKV E3 and E2 proteins (MVA-CHIK) that protected several mouse models from challenge with CHIKV. In particular, BALB/c mice were completely protected against viremia upon challenge with CHIKV after two doses of MVA-CHIK. Additionally, A129 mice (deficient in IFNα/β) were protected from viremia, footpad swelling, and mortality. While high anti-virus antibodies were elicited, low or undetectable levels of neutralizing antibodies were produced in both mouse models. However, passive transfer of MVA-CHIK immune serum to naïve mice did not protect against mortality, suggesting that antibodies may not be the main effectors of protection afforded by MVA-CHIK. Furthermore, depletion of CD4⁺, but not CD8⁺ T-cells from vaccinated mice resulted in 100% mortality, implicating the indispensable role of CD4⁺ T-cells in the protection afforded by MVA-CHIK.

Conclusions/Significance

The results presented herein demonstrate the potential of MVA to effectively express CHIKV E3-E2 proteins and generate protective immune responses. Our findings challenge the assumption that only neutralizing antibodies are effective in providing protection against CHIKV, and provides a framework for the development of novel, more effective vaccine strategies to combat CHIKV.

Chikungunya virus (CHIKV) has recently re-emerged from Africa to cause disease outbreaks in Asia, Europe, and more recently the Caribbean. The virus is transmitted by Aedes mosquitoes and causes a disease that is characterized by high fever and incapacitating joint pain that can cause great personal and economic loss. At present, no approved vaccine or antivirals are approved against CHIKV. In this study, we developed a novel CHIKV vaccine that is vectored by Modified Vaccinia virus Ankara (MVA), an attenuated vaccine vector which has been shown to be safe in humans and induce a strong immune response. The vaccine expresses the E3 and E2 proteins of CHIKV, the latter of which is thought to be the main mediator of protection. The vaccine was effective in two mouse models and protected against all markers of disease tested despite the absence of high levels of neutralizing antibodies, the gold standard of protection. Depletion of CD4+ T cells from vaccinated mice resulted in loss of protection, implicating these cells in the protection induced by the vaccine.

[Chikungunya fever in Mexico: confirmed case and notes on the epidemiologic response]

Chikungunya fever (CHIK) is a viral disease transmitted to human beings by the same vector as dengue -the Aedes mosquito. Besides fever and severe pain in the joints, it produces other symptoms such as myalgias, headache, nausea, fatigue and exanthema. There is no specific treatment for it; the therapeutic management of patients focuses on symptom relief. Historically, outbreaks of large proportions have been reported; even since 2010 it was considered to be a potential emerging epidemic. In 2013 it was introduced into the islands of the Caribbean, and it has recently been reported in the American continent. This paper describes the first confirmed case of chikungunya in Mexico -in the municipality of Tlajomulco de Zúñiga, Jalisco, in May, 2014-, which was imported from the Caribbean island of Antigua and Barbuda by a 39 year-old woman.