From defense to offense: Modulating toll-like receptors to combat arbovirus infections

Arboviruses are a significant threat to global public health, with outbreaks occurring worldwide. Toll-like receptors (TLRs) play a crucial role in the innate immune response against these viruses by recognizing pathogen-associated molecular patterns and initiating an inflammatory response. Significantly, TLRs commonly implicated in the immune response against viral infections include TLR2, TLR4, TLR6, TLR3, TLR7, and TLR8; limiting or allowing them to replicate and spread within the host. Modulating TLRs has emerged as a promising approach to combat arbovirus infections. This review summarizes recent advances in TLR modulation as a therapeutic target in arbovirus infections. Studies have shown that the activation of TLRs can enhance the immune response against arbovirus infections, leading to increased viral clearance and protection against disease. Conversely, inhibition of TLRs can reduce the excessive inflammation and tissue damage associated with arbovirus infection. Modulating TLRs represents a potential therapeutic strategy to combat arbovirus infections.

COVID-19 Therapeutic Potential of Natural Products

Despite the fact that coronavirus disease 2019 (COVID-19) treatment and management are now considerably regulated, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still one of the leading causes of death in 2022. The availability of COVID-19 vaccines, FDA-approved antivirals, and monoclonal antibodies in low-income countries still poses an issue to be addressed. Natural products, particularly traditional Chinese medicines (TCMs) and medicinal plant extracts (or their active component), have challenged the dominance of drug repurposing and synthetic compound libraries in COVID-19 therapeutics. Their abundant resources and excellent antiviral performance make natural products a relatively cheap and readily available alternative for COVID-19 therapeutics. Here, we deliberately review the anti-SARS-CoV-2 mechanisms of the natural products, their potency (pharmacological profiles), and application strategies for COVID-19 intervention. In light of their advantages, this review is intended to acknowledge the potential of natural products as COVID-19 therapeutic candidates.

Knowledge of SARS-CoV-2 Epitopes and Population HLA Types Is Important in the Design of COVID-19 Vaccines

The COVID-19 pandemic has caused extensive loss of lives and economic hardship. In response, infectious disease experts and vaccine developers promptly responded by bringing forth candidate vaccines, some of which have been listed in the World Health Organization’s Emergency Use Listing. Notwithstanding the diverse worldwide population genetics, the vaccines thus far developed are generic in nature for use worldwide. Differences in the human leukocyte antigen (HLA) in different populations, variation of the T cell epitopes, and the propensity of SARS-CoV-2 genetic mutations left room for improvement of the vaccines. Here, we discussed the implications of COVID-19 vaccination and SARS-CoV-2 infection by taking into consideration SARS-CoV-2 mutations, T cell epitopes, risk factors, and current platforms of candidate vaccines based on the HLA types that are commonly present in Peninsular Malaysia Chinese, Indian, and Malay populations. The HLA types associated with protection against and susceptibility to severe SARS-CoV-2 infection were identified based on reported case-control and cohort studies. The relevance of including the non-spike SARS-CoV-2 proteins in the future COVID-19 vaccines is also highlighted. This review is meant to trigger researchers to acknowledge the importance of investigating the possible relationships between the HLA haplotype and the SARS-CoV-2 strains circulating in different populations.

In silico studies of fisetin and silymarin as novel chikungunya virus nonstructural proteins inhibitors

Aim: Chikungunya virus (CHIKV) infection is often characterized by fever, rash and arthralgia. Until now, there is no vaccine or antiviral drug available for this disease. Two flavonoid compounds, silymarin and fisetin, were reported to be able to inhibit CHIKV replication. Materials & methods: The interaction between the flavonoid compounds and two CHIKV nonstructural proteins (nsP2 and nsP3) were investigated through molecular docking supported with other analysis such as molecular dynamics simulation and binding free energy calculation. Results: The compounds establish potent, stable and flexible interaction with the binding pocket of the two target proteins. Conclusion: The outcomes of this study support the previously published experimental data on anti-CHIKV activity of the compounds by highlighting the interactions with the proteins’ key residues.

Inhibition of chikungunya virus replication by hesperetin and naringenin

Chikungunya virus (CHIKV) is an emerging arbovirus, which has recently become globally important.

Seroprevalence report on tick-borne encephalitis virus and Crimean-Congo hemorrhagic fever virus among Malaysian's farm workers

Background

Tick-borne encephalitis virus (TBEV) and Crimean-Congo haemorrhagic fever virus (CCHFV) are important tick-borne viruses. Despite their wide geographical distribution and ease of acquisition, the prevalence of both viruses in Malaysia is still unknown. This study was conducted to determine the seroprevalence for TBEV and CCHFV among Malaysian farm workers as a high-risk group within the population.

Methods

We gave questionnaires to 209 farm workers and invited them to participate in the study. Eighty-five agreed to do so. We then collected and tested sera for the presence of anti-TBEV IgG (immunoglobulin G) and anti-CCHFV IgG using a commercial enzyme-linked immunosorbent assay (ELISA) kit. We also tested seroreactive samples against three other related flaviviruses: dengue virus (DENV), West Nile virus (WNV) and Japanese encephalitis virus (JEV) using the ELISA method.

Results

The preliminary results showed the presence of anti-TBEV IgG in 31 (36.5 %) of 85 sera. However, when testing all the anti-TBEV IgG positive sera against the other three antigenically related flaviviruses to exclude possible cross reactivity, only five (4.2 %) sera did not show any cross reactivity. Interestingly, most (70.97 %) seropositives subjects mentioned tick-bite experience. However, there was no seroreactive sample for CCHFV.

Conclusions

These viruses migrate to neighbouring countries so they should be considered threats for the future, despite the low seroprevalence for TBEV and no serological evidence for CCHFV in this study. Therefore, further investigation involving a large number of human, animal and tick samples that might reveal the viruses’ true prevalence is highly recommended.

Antiviral activity of silymarin against chikungunya virus

The mosquito-borne chikungunya virus (CHIKV) causes chikungunya fever, with clinical presentations such as severe back and small joint pain, and debilitating arthritis associated with crippling pains that persist for weeks and even years. Although there are several studies to evaluate the efficacy of drugs against CHIKV, the treatment for chikungunya fever is mainly symptom-based and no effective licensed vaccine or antiviral are available. Here, we investigated the antiviral activity of three types of flavonoids against CHIKV in vitro replication. Three compounds: silymarin, quercetin and kaempferol were evaluated for their in vitro antiviral activities against CHIKV using a CHIKV replicon cell line and clinical isolate of CHIKV of Central/East African genotype. A cytopathic effect inhibition assay was used to determine their activities on CHIKV viral replication and quantitative reverse transcription PCR was used to calculate virus yield. Antiviral activity of effective compound was further investigated by evaluation of CHIKV protein expression using western blotting for CHIKV nsP1, nsP3, and E2E1 proteins. Briefly, silymarin exhibited significant antiviral activity against CHIKV, reducing both CHIKV replication efficiency and down-regulating production of viral proteins involved in replication. This study may have important consequence for broaden the chance of getting the effective antiviral for CHIKV infection.

First report on the seroprevalence of the Crimean-Congo haemorrhagic fever virus, a tick-borne virus, in Malaysia's Orang Asli population

OBJECTIVE

The Crimean-Congo haemorrhagic fever virus (CCHFV), which is transmitted by the ticks of Hyalomma spp. in general and H. marginatumin particular, can cause severe disease in humans, with mortality rates of 3-30%. Other than from the bites of infected ticks, CCHFV can also be transmitted through contact with patients with the acute phase of infection or contact with blood or tissues from viraemic livestock.  Outbreaks of human cases of haemorrhagic manifestations have been documented since 1945 and described in parts of Africa, Asia, Eastern Europe and the Middle East and most recently India in 2011. In addition, serological evidence of the disease has been reported in some countries where no human cases were reported. As regional neighbours China and India have been affected by this virus, this study was conducted to determine the seroprevalence of CCHFV among Orang Asli population of Malaysia as the most at risk people who residing in the deep forests.

PATIENTS AND METHODS

A total of 682 serum samples were collected from the Orang Asli population residing in eight states in peninsular Malaysia and analysed for the presence of anti-CCHFV immunoglobulin G (IgG) using a commercial enzyme-linked immunosorbent assay kit.

RESULTS

The study subjects comprised 277 (40.6%) men and 405 (59.4%) women. However, anti-CCHFV IgG was detected in only one female serum sample (0.1%). The presence of anti-CCHFV IgG could not be correlated to age or sex from these findings.

CONCLUSIONS

The results of this screening survey showed that the seroprevalence of the anti-CCHFV IgG among Malaysia's Orang Asli population is too low for detection or totally negative compared with that in neighbouring countries, such as India and China.

Baicalin, a metabolite of baicalein with antiviral activity against dengue virus

Baicalin, a flavonoid derived from Scutellaria baicalensis, is the main metabolite of baicalein released following administration in different animal models and human. We previously reported the antiviral activity of baicalein against dengue virus (DENV). Here, we examined the anti-DENV properties of baicalin in vitro, and described the inhibitory potentials of baicalin at different steps of DENV-2 (NGC strain) replication. Our in vitro antiviral experiments showed that baicalin inhibited virus replication at IC50 = 13.5 ± 0.08 μg/ml with SI = 21.5 following virus internalization by Vero cells. Baicalin exhibited virucidal activity against DENV-2 extracellular particles at IC50 = 8.74 ± 0.08 μg/ml and showed anti-adsorption effect with IC50 = 18.07 ± 0.2 μg/ml. Our findings showed that baicalin as the main metabolite of baicalein exerting in vitro anti-DENV activity. Further investigations on baicalein and baicalin to deduce its antiviral therapeutic effects are warranted.

Tick-borne viruses: a review from the perspective of therapeutic approaches

Several important human diseases worldwide are caused by tick-borne viruses. These diseases have become important public health concerns in recent years. The tick-borne viruses that cause diseases in humans mainly belong to 3 families: Bunyaviridae, Flaviviridae, and Reoviridae. In this review, we focus on therapeutic approaches for several of the more important tick-borne viruses from these 3 families. These viruses are Crimean-Congo hemorrhagic fever virus (CCHF) and the newly discovered tick-borne phleboviruses, known as thrombocytopenia syndromevirus (SFTSV), Heartland virus and Bhanja virus from the family Bunyaviridae, tick-borne encephalitis virus (TBEV), Powassan virus (POWV), Louping-ill virus (LIV), Omsk hemorrhagic fever virus (OHFV), Kyasanur Forest disease virus (KFDV), and Alkhurma hemorrhagic fever virus (AHFV) from the Flaviviridae family. To date, there is no effective antiviral drug available against most of these tick-borne viruses. Although there is common usage of antiviral drugs such as ribavirin for CCHF treatment in some countries, there are concerns that ribavirin may not be as effective as once thought against CCHF. Herein, we discuss also the availability of vaccines for the control of these viral infections. The lack of treatment and prevention approaches for these viruses is highlighted, and we hope that this review may increase public health awareness with regard to the threat posed by this group of viruses.