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Chikungunya fever from Malaysia

Yamamoto K, Matumoto K, Lim CK, Moi ML, Kotaki A, Takasaki T

Intern. Med., 2010;49(5):501-5.
PMID: 20190493

An adult Malaysian woman returned to Japan from Kuala Lumpur and had onset of dengue fever-like symptoms including high fever, malaise and arthritis in early January 2009. Serum obtained on the following day was tested at the National Institute of Infectious Diseases in Tokyo, where it was determined to be positive for chikungunya virus (CHIKV) RNA. IgM antibody against CHIKV was negative on January 6 and sero-converted to be positive on January 14, confirming a recent CHIKV infection. Except for arthralgia, all her symptoms resolved uneventfully within 10 days.
Fulltext Erratum to "Characteristics of COVID-19 epidemic and control measures to curb transmission in Malaysia" [Int J Infect Dis 101 (December) (2020) 409-411]

Ng CFS, Seposo XT, Moi ML, Tajudin MABA, Madaniyazi L, Sahani M

Int J Infect Dis, 2021 Jan 19.
PMID: 33483231 DOI: 10.1016/j.ijid.2021.01.024
Fulltext Characteristics of COVID-19 epidemic and control measures to curb transmission in Malaysia

Ng CFS, Seposo XT, Moi ML, Tajudin MABA, Madaniyazi L, Sahani M

Int J Infect Dis, 2020 Dec;101:409-411.
PMID: 33075527 DOI: 10.1016/j.ijid.2020.10.027

The first wave of COVID-19 epidemic began in late January in Malaysia and ended with a very small final size. The second wave of infections broke out in late February and grew rapidly in the first 3 weeks. Authorities in the country responded quickly with a series of control strategies collectively known as the Movement Control Order (MCO) with different levels of intensity matching the progression of the epidemic. We examined the characteristics of the second wave and discussed the key control strategies implemented in the country. In the second wave, the epidemic doubled in size every 3.8 days (95% confidence interval [CI]: 3.3, 4.5) in the first month and decayed slowly after that with a halving time of approximately 3 weeks. The time-varying reproduction number Rt peaked at 3.1 (95% credible interval: 2.7, 3.5) in the 3rd week, declined sharply thereafter and stayed below 1 in the last 3 weeks of April, indicating low transmissibility approximately 3 weeks after the MCO. Experience of the country suggests that adaptive triggering of distancing policies combined with a population-wide movement control measure can be effective in suppressing transmission and preventing a rebound.
Fulltext Dengue virus infection-enhancing activity in serum samples with neutralizing activity as determined by using FcγR-expressing cells

Moi ML, Lim CK, Chua KB, Takasaki T, Kurane I

PLoS Negl Trop Dis, 2012;6(2):e1536.
PMID: 22389741 DOI: 10.1371/journal.pntd.0001536

Progress in dengue vaccine development has been hampered by limited understanding of protective immunity against dengue virus infection. Conventional neutralizing antibody titration assays that use FcγR-negative cells do not consider possible infection-enhancement activity. We reasoned that as FcγR-expressing cells are the major target cells of dengue virus, neutralizing antibody titration assays using FcγR-expressing cells that determine the sum of neutralizing and infection-enhancing activity, may better reflect the biological properties of antibodies in vivo.
Fulltext Whole Genome Sequencing-Based Molecular Epidemiologic Analysis of Autochthonous Dengue Virus Type 1 Strains Circulating in Japan in 2014

Tajima S, Nakayama E, Kotaki A, Moi ML, Ikeda M, Yagasaki K, et al.

Jpn J Infect Dis, 2017 Jan 24;70(1):45-49.
PMID: 27169954 DOI: 10.7883/yoken.JJID.2016.086

Cases of autochthonous infections of dengue virus type 1 (DENV-1) were detected in Japan after a 70-year period devoid of dengue outbreaks. We previously showed that E gene sequences are identical in 11 of the 12 DENV-1 strains autochthonous to Japan. However, the E sequence represents only 14% of the DENV-1 genome. In the present study, we have sequenced the entire genome of 6 autochthonous DENV-1 strains that were isolated from patients during the 2014 outbreak. Sequencing of 5 Yoyogi group strains with identical E sequences and 1 Shizuoka strain with a different E sequence revealed that the first Yoyogi group strain differed from the Shizuoka strain by 18 amino acid residues. Furthermore, 2 Yoyogi group strains had different genomic sequences while the other 3 had identical genomes. Phylogenetic analyses indicated that the Hyogo strain, a Yoyogi group strain, was the first to diverge from the other 4 Yoyogi group strains. The E gene sequence of the Yoyogi group strains exhibits the highest homology to those of the strains isolated in Malaysia and Singapore between 2013 and 2014. The patient infected with the Hyogo strain visited Malaysia before the onset of dengue fever, suggesting that this was a case of dengue infection imported from Malaysia.
Fulltext Genotype-Dependent Immunogenicity of Dengue Virus Type 2 Asian I and Asian/American Genotypes in Common Marmoset (Callithrix jacchus): Discrepancy in Neutralizing and Infection-Enhancing Antibody Levels between Genotypes

Azami NAM, Moi ML, Ami Y, Suzaki Y, Taniguchi S, Tajima S, et al.

Microorganisms, 2021 Oct 21;9(11).
PMID: 34835327 DOI: 10.3390/microorganisms9112196

Owing to genotype-specific neutralizing antibodies, analyzing differences in the immunogenic variation among dengue virus (DENV) genotypes is central to effective vaccine development. Herein, we characterized the viral kinetics and antibody response induced by DENV type 2 Asian I (AI) and Asian/American (AA) genotypes using marmosets (Callithrix jacchus) as models. Two groups of marmosets were inoculated with AI and AA genotypes, and serial plasma samples were collected. Viremia levels were determined using quantitative reverse transcription-PCR, plaque assays, and antigen enzyme-linked immunosorbent assay (ELISA). Anti-DENV immunoglobulin M and G antibodies, neutralizing antibody titer, and antibody-dependent enhancement (ADE) activity were determined using ELISA, plaque reduction neutralization test, and ADE assay, respectively. The AI genotype induced viremia for a longer duration, but the AA genotype induced higher levels of viremia. After four months, the neutralizing antibody titer induced by the AA genotype remained high, but that induced by the AI genotype waned. ADE activity toward Cosmopolitan genotypes was detected in marmosets inoculated with the AI genotype. These findings indicate discrepancies between heterologous genotypes that influence neutralizing antibodies and viremia in marmosets, a critical issue in vaccine development.
Dengue epidemic in Malaysia: urban versus rural comparison of dengue immunoglobulin G seroprevalence among Malaysian adults aged 35-74 years

Azami NAM, Moi ML, Salleh SA, Neoh HM, Kamaruddin MA, Jalal NA, et al.

Trans R Soc Trop Med Hyg, 2020 11 06;114(11):798-811.
PMID: 32735681 DOI: 10.1093/trstmh/traa056

BACKGROUND: A periodic serosurvey of dengue seroprevalence is vital to determine the prevalence of dengue in countries where this disease is endemic. This study aimed to determine the prevalence of dengue immunoglobulin G (IgG) seropositivity among healthy Malaysian adults living in urban and rural areas.
METHODS: A total of 2598 serum samples (1417 urban samples, 1181 rural samples) were randomly collected from adults ages 35-74 y. The presence of the dengue IgG antibody and neutralising antibodies to dengue virus (DENV) 1-4 was determined using enzyme-linked immunosorbent assay and the plaque reduction neutralisation test assay, respectively.
RESULTS: The prevalence of dengue IgG seropositivity was 85.39% in urban areas and 83.48% in rural areas. The seropositivity increased with every 10-y increase in age. Ethnicity was associated with dengue seropositivity in urban areas but not in rural areas. The factors associated with dengue seropositivity were sex and working outdoors. In dengue IgG-positive serum samples, 98.39% of the samples had neutralising antibodies against DENV3, but only 70.97% of them had neutralising antibodies against DENV4.
CONCLUSION: The high seroprevalence of dengue found in urban and rural areas suggests that both urban and rural communities are vital for establishing and sustaining DENV transmission in Malaysia.