Prospects for dengue vaccines for travelers

Enhanced dengue vaccine virus replication and neutralizing antibody responses in immune primed rhesus macaques

Antibody-dependent enhancement (ADE) is suspected to influence dengue virus (DENV) infection, but the role ADE plays in vaccination strategies incorporating live attenuated virus components is less clear. Using a heterologous prime-boost strategy in rhesus macaques, we examine the effect of priming with DENV purified inactivated vaccines (PIVs) on a tetravalent live attenuated vaccine (LAV). Sera exhibited low-level neutralizing antibodies (NAb) post PIV priming, yet moderate to high in vitro ADE activity. Following LAV administration, the PIV primed groups exhibited DENV-2 LAV peak viremias up to 1,176-fold higher than the mock primed group, and peak viremia correlated with in vitro ADE. Furthermore, PIV primed groups had more balanced and higher DENV-1–4 NAb seroconversion and titers than the mock primed group following LAV administration. These results have implications for the development of effective DENV vaccine prime-boost strategies and for our understanding of the role played by ADE in modulating DENV replication.

A Two-Patch Mathematical Model for Temperature-Dependent Dengue Transmission Dynamics

Dengue fever has been a threat to public health not only in tropical regions but non-tropical regions due to recent climate change. Motivated by a recent dengue outbreak in Japan, we develop a two-patch model for dengue transmission associated with temperature-dependent parameters. The two patches represent a park area where mosquitoes prevail and a residential area where people live. Based on climate change scenarios, we investigate the dengue transmission dynamics between the patches. We employ an optimal control method to implement proper control measures in the two-patch model. We find that blockage between two patches for a short-term period is effective in a certain degree for the disease control, but to obtain a significant control effect of the disease, a long-term blockage should be implemented. Moreover, the control strategies such as vector control and transmission control are very effective, if they are implemented right before the summer outbreak. We also investigate the cost-effectiveness of control strategies such as vaccination, vector control and virus transmission control. We find that vector control and virus transmission control are more cost-effective than vaccination in case of Korea.

Efficient Delivery of Dengue Virus Subunit Vaccines to the Skin by Microprojection Arrays

Dengue virus is the most important arbovirus impacting global human health, with an estimated 390 million infections annually, and over half the world’s population at risk of infection. While significant efforts have been made to develop effective vaccines to mitigate this threat, the task has proven extremely challenging, with new approaches continually being sought. The majority of protective, neutralizing antibodies induced during infection are targeted by the envelope (E) protein, making it an ideal candidate for a subunit vaccine approach. Using truncated, recombinant, secreted E proteins (sE) of all 4 dengue virus serotypes, we have assessed their immunogenicity and protective efficacy in mice, with or without Quil-A as an adjuvant, and delivered via micropatch array (MPA) to the skin in comparison with more traditional routes of immunization. The micropatch contains an ultra-high density array (21,000/cm²) of 110 μm microprojections. Mice received 3 doses of 1 μg (nanopatch, intradermal, subcutaneous, or intra muscular injection) or 10 μg (intradermal, subcutaneous, or intra muscular injection) of tetravalent sE spaced 4 weeks apart. When adjuvanted with Quil-A, tetravalent sE vaccination delivered via MPA resulted in earlier induction of virus-neutralizing IgG antibodies for all four serotypes when compared with all of the other vaccination routes. Using the infectious dengue virus AG129 mouse infectious dengue model, these neutralizing antibodies protected all mice from lethal dengue virus type 2 D220 challenge, with protected animals showing no signs of disease or circulating virus. If these results can be translated to humans, MPA-delivered sE represents a promising approach to dengue virus vaccination.

Antiviral activity of betacyanins from red pitahaya (Hylocereus polyrhizus) and red spinach (Amaranthus dubius) against dengue virus type 2 (GenBank accession no. MH488959)

This study investigated the antiviral activity of betacyanins from red pitahaya (Hylocereus polyrhizus) and red spinach (Amaranthus dubius) against dengue virus type 2 (DENV-2). The pulp of red pitahaya and the leaves of red spinach were extracted using methanol followed by sub-fractionation and Amberlite XAD16N column chromatography to obtain betacyanin fractions. The half maximum cytotoxicity concentration for betacyanin fractions from red pitahaya and red spinach on Vero cells were 4.346 and 2.287 mg ml-1, respectively. The half-maximal inhibitory concentration (IC50) of betacyanin fraction from red pitahaya was 125.8 μg ml-1 with selectivity index (SI) of 5.8. For betacyanin fraction from red spinach, the IC50 value was 14.62 µg ml-1 with SI of 28.51. Using the maximum non-toxic betacyanin concentration, direct virucidal effect against DENV-2 was obtained from betacyanin fraction from red pitahaya (IC50 of 126.70 μg ml-1; 95.0 % virus inhibition) and red spinach (IC50 value of 106.80 μg ml-1; 65.9 % of virus inhibition). Betacyanin fractions from red pitahaya and red spinach inhibited DENV-2 in vitro.

Preventing diseases in round-the-world travelers: a contemporary challenge for travel medicine advice

Providing advice for travelers embarking on long-term trips poses a challenge in travel medicine. A long duration of risk exposure is associated with underuse of protective measures and poor adherence to chemoprophylaxis, increasing the chances of acquiring infections. Recently, in our clinic, we observed an increase in the number of travelers undertaking round-the-world trips. These individuals are typically aged around 32 years and quit their jobs to embark on one-to-two-year journeys. Their destinations include countries in two or more continents, invariably Southeast Asia and Indonesia, and mostly involve land travel and visiting rural areas. Such trips involve flexible plans, increasing the challenge, especially with regard to malaria prophylaxis. Advising round-the-world travelers is time-consuming because of the amount of information that must be provided to the traveler. Advisors must develop strategies to commit the traveler to his/her own health, and verify their learnings on disease-prevention measures. Contacting the advisor after the appointment or during the trip can be helpful to clarify unclear instructions or diagnosis made and prescriptions given abroad. Infectious diseases are among the most frequent problems affecting travelers, many of which are preventable by vaccines, medicines, and precautionary measures. The dissemination of counterfeit medicines, particularly antibiotics and antimalarial medicines, emphasizes the need for travelers to carry medicines that they may possibly need on their trip. Additional advice on altitude, scuba diving, and other possible risks may also be given. Considering the difficulties in advising this group, we present a review of the main recommendations on advising these travelers.

Dengue-associated hemophagocytic lymphohistiocytosis in an adult: A case report and literature review

BACKGROUND

Infection-associated hemophagocytic syndrome (IAHS) is potentially a fatal disease caused by systemic infection complicated by hemophagocyticlymphohistiocytosis (HLH). Here, we report a case of HLH associated with dengue hemorrhagic fever (DHF) after a trip to Thailand.

CASE SUMMARY

A 33-year-old healthy female patient presented with 3 days of fever, myalgia, and skin rash. Serotype 3 dengue virus was isolated. Clinical and laboratory findings fulfilled the criteria of HLH. After the initiation of corticosteroid therapy, the patient recovered and laboratory findings were normalized.

CONCLUSION

It would be important to differentially diagnose dengue-associated HLH from severe DHF. Early recognition and initiation of steroid treatment would be crucial for the successful treatment of dengue fever complicated by HLH.