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The antibody isotype IgM appears earlier than IgG, within days of onset of symptoms, and is important during the early stages of the adaptive immune response. Little is known about the functional role of IgM during infection with chikungunya virus (CHIKV), a recently reemerging arbovirus that has caused large global outbreaks. In this study, we studied antibody responses in 102 serum samples collected during CHIKV outbreaks in Malaysia. We described the neutralizing role of IgM at different times post-infection and examined the independent contributions of IgM and IgG towards the neutralizing capacity of human immune sera during the early phase of infection, including the differences in targets of neutralizing epitopes. Neutralizing IgM starts to appear as early as day 4 of symptoms, and their appearance from day 6 is associated with a reduction in viremia. IgM acts in a complementary manner with the early IgG, but plays the main neutralizing role up to a point between days 4 and 10 which varies between individuals. After this point, total neutralizing capacity is attributable almost entirely to the robust neutralizing IgG response. IgM preferentially binds and targets epitopes on the CHIKV surface E1-E2 glycoproteins, rather than individual E1 or E2. These findings provide insight into the early antibody responses to CHIKV, and have implications for design of diagnostic serological assays.

Mosquito-borne Chikungunya virus (CHIKV) has recently re-emerged globally. The epidemic East/Central/South African (ECSA) strains have spread for the first time to Asia, which previously only had endemic Asian strains. In Malaysia, the ECSA strain caused an extensive nationwide outbreak in 2008, while the Asian strains only caused limited outbreaks prior to this. To gain insight into these observed epidemiological differences, we compared genotypic and phenotypic characteristics of CHIKV of Asian and ECSA genotypes isolated in Malaysia. CHIKV of Asian and ECSA genotypes were isolated from patients during outbreaks in Bagan Panchor in 2006, and Johor in 2008. Sequencing of the CHIKV strains revealed 96.8% amino acid similarity, including an unusual 7 residue deletion in the nsP3 protein of the Asian strain. CHIKV replication in cells and Aedes mosquitoes was measured by virus titration. There were no differences in mammalian cell lines. The ECSA strain reached significantly higher titres in Ae. albopictus cells (C6/36). Both CHIKV strains infected Ae. albopictus mosquitoes at a higher rate than Ae. aegypti, but when compared to each other, the ECSA strain had much higher midgut infection and replication, and salivary gland dissemination, while the Asian strain infected Ae. aegypti at higher rates. The greater ability of the ECSA strain to replicate in Ae. albopictus may explain why it spread far more quickly and extensively in humans in Malaysia than the Asian strain ever did, particularly in rural areas where Ae. albopictus predominates. Intergenotypic genetic differences were found at E1, E2, and nsP3 sites previously reported to be determinants of host adaptability in alphaviruses. Transmission of CHIKV in humans is influenced by virus strain and vector species, which has implications for regions with more than one circulating CHIKV genotype and Aedes species.

To describe the severity, human adenovirus (HAdV) type and respiratory morbidity following adenovirus pneumonia in children. Retrospective review of children under 12 years of age, admitted with HAdV pneumonia, between January 2011 and July 2013, in a single centre in Malaysia. HAdV isolated from nasopharyngeal secretions were typed by sequencing hypervariable regions 1-6 of the hexon gene. Patients were reviewed for respiratory complications. HAdV was detected in 131 children of whom 92 fulfilled inclusion criteria. Median (range) age was 1.1 (0.1-8.0) years with 80% under 2 years. Twenty percent had severe disease with a case-fatality rate of 5.4%. Duration of admission (p = 0.02) was independently associated with severe illness. Twenty-two percent developed respiratory complications, the commonest being bronchiolitis obliterans (15.2%) and recurrent wheeze (5.4%). The predominant type shifted from HAdV1 and HAdV3 in 2011 to HAdV7 in 2013. The commonest types identified were types 7 (54.4%), 1(17.7%) and 3 (12.6%). Four out of the five patients who died were positive for HAdV7. Infection with type 7 (OR 8.90, 95% CI 1.32, 59.89), family history of asthma (OR 14.80, 95% CI 2.12-103.21) and need for invasive or non-invasive ventilation (OR 151.84, 95% CI 9.93-2.32E) were independent predictors of respiratory complications. One in five children admitted with HAdV pneumonia had severe disease and 22% developed respiratory complications. Type 7 was commonly isolated in children with severe disease. Family history of asthma need for invasive or non-invasive ventilation and HAdV 7 were independent predictors of respiratory complications.

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.

[This corrects the article DOI: 10.1371/journal.pone.0205795.].

Chikungunya virus (CHIKV), an alphavirus of the family Togaviridae,causes fever, polyarthritis, and rash. There are three genotypes: West African, Asian, and East, Central and South African (ECSA). The latter two genotypes have caused outbreaks in Malaysia. Recent ECSA CHIKV outbreaks have been associated with severe neurological disease including encephalitis, meningitis, and acute flaccid paralysis. It is not known if different CHIKV genotypes are associated with different severity of neurological disease. In this study, the neurovirulence of Asian (MY/06/37348) and ECSA (MY/08/065) strains of CHIKV were compared by intracerebral inoculation in suckling mice, followed by virus titration, quantitative real-time PCR, histopathology, and gene expression analysis of the harvested brains. Both genotypes of CHIKV replicated similarly in the brains, yet suckling mice infected with Asian CHIKV showed higher mortality compared to ECSA CHIKV-infected mice and control mice. Histopathologic analysis showed that both CHIKV genotypes were found to spread within the brain (where CHIKV antigen was localised to astrocytes and neurons) and beyond to skeletal muscle. In Asian CHIKV-infected suckling mice, apoptosis and necrosis were observed earlier in brains, and more extensive CHIKV spread and pathologic changes were seen in skeletal muscle. Gene expression analysis showed that pro-apoptotic genes (eIF2αK2) were upregulated at higher levels in Asian CHIKVinfected suckling mice, while genes involved in anti-apoptosis (BIRC3) and antiviral responses and CNS protection (CD40, IL-10RA, MyD88, and PYCARD) were upregulated more highly in ECSA CHIKV-infected suckling mice. In conclusion, these findings suggest that the higher mortality observed following Asian CHIKV infection in mice is not due to higher viral replication in the brain as there was more spread in muscle and due to differentially expressed genes involved in antiviral activity and CNS protection. Further studies could focus on the differences in viral sequences encoding neurovirulence determinants. This information on important host responses may be used for development of therapeutic and prophylactic strategies against CHIKV infection, and identification of biomarkers for neurological CHIKV infections.