Valine/isoleucine variants drive selective pressure in the VP1 sequence of EV-A71 enteroviruses.

BACKGROUND: In 2011-2012, Northern Vietnam experienced its first large scale hand foot and mouth disease (HFMD) epidemic. In 2011, a major HFMD epidemic was also reported in South Vietnam with fatal cases. This 2011-2012 outbreak was the first one to occur in North Vietnam providing grounds to study the etiology, origin and dynamic of the disease. We report here the analysis of the VP1 gene of strains isolated throughout North Vietnam during the 2011-2012 outbreak and before. METHODS: The VP1 gene of 106 EV-A71 isolates from North Vietnam and 2 from Central Vietnam were sequenced. Sequence alignments were analyzed at the nucleic acid and protein level. Gene polymorphism was also analyzed. A Factorial Correspondence Analysis was performed to correlate amino acid mutations with clinical parameters. RESULTS: The sequences were distributed into four phylogenetic clusters. Three clusters corresponded to the subgenogroup C4 and the last one corresponded to the subgenogroup C5. Each cluster displayed different polymorphism characteristics. Proteins were highly conserved but three sites bearing only Isoleucine (I) or Valine (V) were characterized. The isoleucine/valine variability matched the clusters. Spatiotemporal analysis of the I/V variants showed that all variants which emerged in 2011 and then in 2012 were not the same but were all present in the region prior to the 2011-2012 outbreak. Some correlation was found between certain I/V variants and ethnicity and severity. CONCLUSIONS: The 2011-2012 outbreak was not caused by an exogenous strain coming from South Vietnam or elsewhere but by strains already present and circulating at low level in North Vietnam. However, what triggered the outbreak remains unclear. A selective pressure is applied on I/V variants which matches the genetic clusters. I/V variants were shown on other viruses to correlate with pathogenicity. This should be investigated in EV-A71. I/V variants are an easy and efficient way to survey and identify circulating EV-A71 strains.

Monitoring the Influence of Hand, Foot, and Mouth Disease: New Guidelines on Patient Care during the 2011-2012 Multiwaves and Multivariant Outbreak in Hai Phong City, Vietnam.

From 2011 to 2012, Northern Vietnam suffered its first large-scale hand, foot, and mouth disease (HFMD) epidemic. Two sets of official guidelines were issued during the outbreak to handle the HFMD crisis. The city of Hai Phong was used as a model to analyze the impact of the released guidelines. A total of 9621 HFMD cases were reported in Hai Phong city from April 2011 to December 2012. Three distinct waves of HFMD occurred. Enterovirus A71 and Coxsackievirus A16 were successively associated with the epidemics. Two periods, before and after the guidelines' release, could be distinguished and characterized by different patient patterns. The time to admission and severity changed notably. Guideline publications help the health system refocus on the 0.5-3 years age group with the highest incidence of the disease. The three waves showed different special distribution, but the main routes of infection were rivers and local secondary roads, most likely through local trade and occupational movements of people.

Coxsackieviruses A6 and A16 associated with hand, foot, and mouth disease in Vietnam, 2008-2017: Essential information for rational vaccine design.

Development of multivalent hand, foot, and mouth disease (HFMD) vaccines against enterovirus A71 (EV-A71) and several non-EV-A71 enteroviruses is needed for this life-threatening disease with a huge economic burden in Asia-Pacific countries. Comprehensive studies on the molecular epidemiology and genetic and antigenic characterization of major causative enteroviruses will provide information for rational vaccine design. Compared with molecular studies on EV-A71, that for non-EV-A71 enteroviruses remain few and limited in Vietnam. Therefore, we conducted a 10-year study on the circulation and genetic characterization of coxsackievirus A16 (CV-A16) and CV-A6 isolated from patients with HFMD in Northern Vietnam between 2008 and 2017. Enteroviruses were detected in 2228 of 3212 enrolled patients. Of the 42 serotypes assigned, 28.4% and 22.4% accounted for CV-A6 and CV-A16, being the second and the third dominant serotypes after EV-A71 (31.7%), respectively. The circulation of CV-A16 and CV-A6 showed a wide geographic distribution and distinct periodicity. Phylogenetic analyses revealed that the majority of Vietnamese CV-A6 and CV-A16 strains were located within the largest sub-genotypes or sub-genogroups. These comprised strains isolated from patients with HFMD worldwide during the past decade and the Vietnamese strains have been evolving in a manner similar to the strains circulating worldwide. Amino acid sequences of the putative functional loops on VP1 and other VPs among Vietnamese CV-A6 and CV-A16 isolates were highly conserved. Moreover, the functional loop patterns of VP1 were similar to the dominant patterns found worldwide, except for the T164K substitution on the EF loop in Vietnamese CV-A16. The findings suggest that the development of a universal HFMD vaccine, at least in Vietnam, must target CV-A6 and CV-A16 as two of the three major HFMD-causing serotypes. Vietnamese isolates or their genome sequences can be considered for rational vaccine design.

Epidemiological profile and burden of rotavirus diarrhea in Vietnam: 5 years of sentinel hospital surveillance, 1998-2003.

For 5 years, we have conducted sentinel surveillance for rotavirus at 6 hospitals in 4 cities in Vietnam. Stool samples obtained from >10,000 children <5 years old who were admitted to the hospital with diarrhea have been screened for rotavirus. Overall, 55% of samples were positive, and there was little variability in rates of detection of rotavirus between sites (44%-62%). In Vietnam, the characteristics of rotavirus infection more closely resemble those seen in developed countries, rather than those seen in developing countries: children become infected at an older age, the percentage of stool samples in which rotavirus is detected is extremely high, and the rotavirus strains appear to be the common types, with fewer mixed infections occurring. It is estimated that 5300-6800 children <5 years old die of rotavirus infection each year in Vietnam, representing 8%-11% of all deaths in this age group (cumulative risk per child by age 5 years, 1 in 200 to 1 in 285). Additional studies are ongoing to document the economic cost of the disease and to assess the burden of both fatal cases and milder cases of disease. Study outcomes will provide information for future testing and potential use of a rotavirus vaccine.