Epidemiological and virological factors determining dengue transmission in Sri Lanka during the COVID-19 pandemic

Simultaneous Cocirculation of 2 Genotypes of Dengue Virus Serotype 3 Causing a Large Outbreak in Sri Lanka in 2023

BACKGROUND

We observed a discrepancy between dengue NS1 antigen test and molecular diagnostics, with the emergence of dengue virus (DENV) serotype 3 in Sri Lanka, and sought to understand the cause for the rise in cases and high failure rates of molecular diagnostics.

METHODS

Whole-genome sequencing was carried out in 22 DENV-3 samples. Phylogenetic and molecular clock analyses were done for genotype assignment and to understand the rate of evolution. Mutation analysis was done to understand the reasons for polymerase chain reaction (PCR) nondetection.

RESULTS

We identified 2 DENV-3 genotypes (I and III) cocirculating. DENV-3 genotype III strains shared a common ancestor with a sequence from India collected in 2022, while DENV-3 genotype I, was found to share a common ancestor with DENV-3 sequences from China. DENV-3 genotype III was detected by the modified Centers for Disease Control and Prevention DENV-3 primers, whereas genotype I evaded detection due to key mutations at forward and reverse primer binding sites. We identified point mutations C744T and A756G in the forward primer binding sites and G795A in the reverse primer binding sites, which were not identified in DENV-3 genotype III. Furthermore, our Sri Lankan DENV-3 strains demonstrated a high root to tip ratio compared to the previous DENV-3 sequences, indicating a high mutation rate during the time of sampling (2017 to 2023).

CONCLUSIONS

The cocirculation of multiple genotypes associated with an increase in cases highlights the importance of continuous surveillance of DENVs to identify mutations resulting in nondetection by diagnostics and differences in virulence.

Incidence and co-infection with COVID-19 of dengue during the COVID-19 pandemic

The co-infection of dengue and COVID-19 has been regarded as a public health issue for dengue-endemic countries during the COVID-19 pandemic. Travel restrictions might decrease the chance of mosquitoes biting and, thus, reduce the risk of dengue transmission. However, the spread of dengue was reported to increase with the policies of lockdowns and social distancing in specific areas due to delayed interventions in dengue transmission. Of cases experiencing dengue and COVID-19 co-infection, most recovered after receiving supportive care and/or steroid therapy. However, some episodes of severe or fatal diseases in specific individuals, such as pregnant women, have been reported, and the clinical course of this co-infection is unrecognized or unpredictable. Accordingly, it is crucial to promptly identify predictors of developing severe viral diseases among co-infection patients.

Per vaginal bleeding-an important but ignored feature of dengue

Background

Elderly individuals, those with comorbidities and pregnant women are at a higher risk of developing severe dengue and succumbing to their illness. However, an increased incidence of severe dengue and fatalities are seen in females of the reproductive age. As per vaginal (PV) bleeding is an important complication that has not been well characterized, we sought to determine the frequency, complications and disease outcomes in women who develop PV bleeding.

Methodology/Principal findings

288 adult female patients were recruited from the National Institute of Infectious Diseases Sri Lanka. All clinical features and laboratory investigations were recorded throughout the duration of hospital admission along with treatment received.28/288 (9.72%) reported PV bleeding, with 12/28 (42.85%) developing dengue haemorrhagic fever (DHF) compared to 65/260 (25%) of those who did not have bleeding.Women who developed PV bleeding were more likely to have developed DHF (OR 2.2, 95% CI 0.98 to 5.1, p=0.06), abdominal pain (OR=2.17, 95% CI = 0.99 to 4.69, p = 0.06), vomiting (OR= 2.0, 95% CI= 0.89 to 4.44, p= 0.10), diarhoea (OR= 4.35, 95% CI = 1.908 to 9.610, p= 0.0004) or evidence of any fluid leakage (OR= 1.98, 95% CI = 0.91 to 4.5, p = 0.11). Although not significant, those who had PV bleeding were more likely to have been given intravenous fluids, blood transfusions and colloids.

Conclusions

PV bleeding appears to associate with worse disease outcomes. The possible contribution of PV bleeding to higher incidence of severe dengue and fatality rates observed in many countries, should be further investigated.

Rapid human movement and dengue transmission in Bangladesh: a spatial and temporal analysis based on different policy measures of COVID-19 pandemic and Eid festival

BACKGROUND

Rapid human movement plays a crucial role in the spatial dissemination of the dengue virus. Nevertheless, robust quantification of this relationship using both spatial and temporal models remains necessary. This study aims to explore the spatial and temporal patterns of dengue transmission under various human movement contexts.

METHODS

We obtained district-wise aggregated dengue incidence data from the Management Information System, Directorate General of Health Services of Bangladesh. The stringency index (SI), along with eight individual policy measures (from the Oxford Coronavirus Government Response Tracker database) and six mobility indices (as measured by Google's Community Mobility Reports) were obtained as human movement indicators. A multi-step correlative modelling approach, including various spatial and temporal models, was utilized to explore the associations of dengue incidence with the SI, fourteen human movement indices and the Eid festival.

RESULTS

The global Moran's I indicated significant spatial autocorrelation in dengue incidence during the pre-pandemic (Moran's I: 0.14, P < 0.05) and post-pandemic periods (Moran's I: 0.42, P < 0.01), while the pandemic period (2020-2022) showed weaker, non-significant spatial clustering (Moran's I: 0.07, P > 0.05). Following the pandemic, we identified the emergence of new dengue hotspots. We found a strong negative relationship between monthly dengue incidence and the SI (rspearman: - 0.62, P < 0.01). Through the selection of an optimal Seasonal autoregressive integrated moving average model, we observed that the closure of public transport (β = - 1.66, P < 0.10) and restrictions on internal movement (β = - 2.13, P < 0.10) were associated with the reduction of dengue incidence. Additionally, observed cases were substantially lower than predicted cases during the period from 2020 to 2022. By utilising additional time-series models, we were able to identify in 2023 a rise in dengue incidence associated with the Eid festival intervention, even after adjusting for important climate variables.

CONCLUSIONS

Overall, rapid human movement was found to be associated with increased dengue transmission in Bangladesh. Consequently, the implemention of effective mosquito control interventions prior to large festival periods is necessary for preventing the spread of the disease nationwide. We emphasize the necessity for developing advanced surveillance and monitoring networks to track real-time human movement patterns and dengue incidence.

Identifying the strains of dengue circulating in the western province of Sri Lanka during 2019-2022

A study conducted from July 2019 to May 2022 at several hospitals in the Western Province, Sri Lanka, focused on dengue virus strains during the COVID-19 pandemic. Among 417 febrile patients, 47% were PCR-positive for dengue. Serotyping revealed DENV-1 (12.8%), DENV-2 (46.4%), DENV-3 (37.2%), and DENV-4 (3.6%). Sequencing identified two genotypically distinct variants of DENV-3 and two genotypically distinct variants of DENV-1, while DENV-2 showed a single genotype cluster. Notably, the study found concurrent circulation of two DENV-3 and two DENV-1 genotypes, along with DENV-2, during the pandemic in the area. This data suggests the presence of multiple dengue strains, including several DENV-1 and DENV-3 variants, without major epidemic outbreaks reported in the Western Province. Continuous monitoring and research are essential to understand the dynamics of these dengue strains in the context of the COVID-19 pandemic.

Simultaneous co-circulation of two genotypes of dengue virus serotype 3 causing a large outbreak in Sri Lanka in year 2023

As many other countries, Sri Lanka experienced a marked rise in the number of dengue cases in 2023, with an unusual pattern of disease epidemiology. This rise coincided with the emergence of dengue virus (DENV) serotype 3 in Sri Lanka as the predominant serotype after 2009. Interestingly, a discrepancy between NS1 rapid antigen test positivity and quantitative real time PCR positivity was observed, with 50% of NS1 positive samples being negative by molecular diagnostics. Following sequencing of the DENV-3 strains in 2023, we identified two DENV-3 genotypes (I and III) co-circulating. While DENV-3 genotype III was detected by the modified CDC DENV-3 primers, genotype I evaded detection due to key mutations at forward and reverse primer binding sites. The co-circulation of multiple genotypes associated with an increase in cases highlights the importance of continuous surveillance of DENVs to identify mutations resulting in non-detection by diagnostics and differences in virulence.

Dengue overview: An updated systemic review

Dengue is caused by the dengue virus (DENVs) infection and clinical manifestations include dengue fever (DF), dengue hemorrhagic fever (DHF), or dengue shock syndrome (DSS). Due to a lack of antiviral drugs and effective vaccines, several therapeutic and control strategies have been proposed. A systemic literature review was conducted according to PRISMA guidelines to select proper references to give an overview of DENV infection. Results indicate that understanding the virus characteristics and epidemiology are essential to gain the basic and clinical knowledge as well as dengue disseminated pattern and status. Different factors and mechanisms are thought to be involved in the presentation of DHF and DSS, including antibody-dependent enhancement, immune dysregulation, viral virulence, host genetic susceptibility, and preexisting dengue antibodies. This study suggests that dissecting pathogenesis and risk factors as well as developing different types of therapeutic and control strategies against DENV infection are urgently needed.

Antibody and memory B cell responses to the dengue virus NS1 antigen in individuals with varying severity of past infection

To further understand the role of NS1-specific antibodies (Abs) in disease pathogenesis, we compared neutralizing antibody levels (Nabs), NS1-Ab levels, IgG antibody subclass profiles and NS1-specific memory B-cell responses (Bmems) in individuals, with varying severity of past dengue. Nabs (Neut50 titres) were assessed using the Foci Reduction Neutralization Test (FRNT) and in-house ELISAs were used to assess NS1-Abs and NS1-Ab subclasses for all four DENV serotypes in individuals with past DF (n = 22), those with past DHF (n = 14) and seronegative (SN) individuals (n = 7). B-cell ELISpot assays were used to assess NS1-specific Bmem responses. 15/22 (68.18%) individuals with past DF and 9/14 (64.29%) individuals with past DHF had heterotypic infections. Neut50 titres were found to be significantly higher for DENV1 than DENV2 (p = 0.0006) and DENV4 (p = 0.0127), in those with past DHF, whereas there was no significant difference seen in titres for different DENV serotypes in those with past DF. Overall NS1-Ab to all serotypes and NS1-specific IgG1 responses for DENV1, 2 and 4 serotypes were significantly higher in those with past DHF than individuals with past DF. Those with past DHF also had higher IgG1 than IgG3 for DENV1 and DENV3, whereas no differences were seen in those with past DF. Over 50% of those with past DF or DHF had NS1-specific Bmem responses to >2 DENV serotypes. There was no difference in the frequency of Bmem responses to any of the DENV serotypes between individuals with past DF and DHF. Although the frequency of Bmem responses to DENV1 correlated with DENV1-specific NS1-Abs levels (Spearman r = 0.35, p = 0.02), there was no correlation with other DENV serotypes. We found that those with past DF had broadly cross-reactive Nabs, while those with past DHF had higher NS1-Ab responses possibly with a different functionality profile than those with past DF. Therefore, it would be important to further evaluate the functionality of NS1-specific antibody and Bmem responses to find out the type of antibody repertoire that is associated with protection against severe disease.

Dengue Incidence and Aedes Vector Collections in Relation to COVID-19 Population Mobility Restrictions

Contrary to expectation, dengue incidence decreased in many countries during the period when stringent population movement restrictions were imposed to combat COVID-19. Using a seasonal autoregressive integrated moving average model, we previously reported a 74% reduction in the predicted number of dengue cases from March 2020 to April 2021 in the whole of Sri Lanka, with reductions occurring in all 25 districts in the country. The reduction in dengue incidence was accompanied by an 87% reduction in larval collections of Aedes vectors in the northern city of Jaffna. It was proposed that movement restrictions led to reduced human contact and blood feeding by Aedes vectors, accompanied by decreased oviposition and vector densities, which were responsible for diminished dengue transmission. These findings are extended in the present study by investigating the relationship between dengue incidence, population movement restrictions, and vector larval collections between May 2021 and July 2022, when movement restrictions began to be lifted, with their complete removal in November 2021. The new findings further support our previous proposal that population movement restrictions imposed during the COVID-19 pandemic reduced dengue transmission primarily by influencing human-Aedes vector interaction dynamics.