Despite the presence of dengue in Sri Lanka since the early 1960s, dengue has become a major public health issue, with a high morbidity and mortality. Aedes aegypti and Aedes albopictus are the vectors responsible for the transmission of dengue viruses (DENV). The four DENV serotypes (1, 2, 3, and 4) have been co-circulating in Sri Lanka for more than 30 years. The new genotype of DENV-1 has replaced an old genotype, and new clades of DENV-3 genotype III have replaced older clades. The emergence of new clades of DENV-3 in the recent past coincided with an abrupt increase in the number of dengue fever (DF)/dengue hemorrhagic fever (DHF) cases, implicating this serotype in severe epidemics. Climatic factors play a pivotal role in the epidemiological pattern of DF/DHF in terms of the number of cases, severity of illness, shifts in affected age groups, and the expansion of spread from urban to rural areas. There is a regular incidence of DF/DHF throughout the year, with the highest incidence during the rainy months. To reduce the morbidity and mortality associated with DF/DHF, it is important to implement effective vector control programs in the country. The economic impact of DF/DHF results from the expenditure on DF/DHF critical care units in several hospitals and the cost of case management.

Mosquitoes live under the endless threat of infections from different kinds of pathogens such as bacteria, parasites, and viruses. The mosquito defends itself by employing both physical and physiological barriers that resist the entry of the pathogen and the subsequent establishment of the pathogen within the mosquito. However, if the pathogen does gain entry into the insect, the insect mounts a vigorous innate cellular and humoral immune response against the pathogen, thereby limiting the pathogen’s propagation to nonpathogenic levels. This happens through three major mechanisms: phagocytosis, melanization, and lysis. During these processes, various signaling pathways that engage intense mosquito–pathogen interactions are activated. A critical overview of the mosquito immune system and latest information about the interaction between mosquitoes and pathogens are provided in this review. The conserved, innate immune pathways and specific anti-pathogenic strategies in mosquito midgut, hemolymph, salivary gland, and neural tissues for the control of pathogen propagation are discussed in detail.

Dengue is one of the major hurdles to the public health in Sri Lanka, causing high morbidity and mortality. The present study focuses on the use of geographical information systems (GIS) to map and evaluate the spatial and temporal distribution of dengue in Sri Lanka from 2009 to 2014 and to elucidate the association of climatic factors with dengue incidence. Epidemiological, population and meteorological data were collected from the Epidemiology Unit, Department of Census and Statistics and the Department of Meteorology of Sri Lanka. Data were analyzed using SPSS (Version 20, 2011) and R studio (2012) and the maps were generated using Arc GIS 10.2. The dengue incidence showed a significant positive correlation with rainfall (p<0.0001). No positive correlation was observed between dengue incidence and temperature (p = 0.107) or humidity (p = 0.084). Rainfall prior to 2 and 5 months and a rise in the temperature prior to 9 months positively correlated with dengue incidence as based on the auto-correlation values. A rise in humidity prior to 1 month had a mild positive correlation with dengue incidence. However, a rise in humidity prior to 9 months had a significant negative correlation with dengue incidence based on the auto-correlation values. Remote sensing and GIS technologies give near real time utility of climatic data together with the past dengue incidence for the prediction of dengue outbreaks. In that regard, GIS will be applicable in outbreak predictions including prompt identification of locations with dengue incidence and forecasting future risks and thus direct control measures to minimize major outbreaks.

Circulation of multiple dengue virus (DENV) serotypes in a locale has resulted in individuals becoming infected with mixed serotypes. This research was undertaken to study the clinical presentation, presence of DENV serotypes and serological characteristics of DENV infected patients with co-infections from three Provinces of Sri Lanka where DENV-1 and -2 predominated during the study. A reverse transcription polymerase chain reaction was performed on 1249 patient samples and 301 were positive for DENV (24.1%). DENV-1 was the predominant serotype detected in 137 (45.51%) followed by DENV-2 in 65 (21.59%), DENV-3 in 59 (19.6%) and DENV-4 in 4 (1.32%) patients with mono-infections. Thirty-three patients (10.96%) had DENV co-infections with two or more serotypes. The highest number of co-infections was noted between DENV-1 and DENV-2 (57.57%) suggesting co-infection is driven by the frequency of the circulating serotypes. Platelet counts were significantly higher in DENV co-infected patients although clinical disease severity or white blood cell count, packed cell volume or viraemia were not significantly different in the co-infected compared to the mono-infected patients. Thus co-infection with multiple DENV serotypes does occur but with the exception of improved platelet counts in co-infected patients, there is no evidence that clinical or laboratory measures of disease are altered.

Dengue is an acute viral or viral haemorrhagic fever caused by a flavivirus of four well-known serotypes (DENV-1, DENV-2, DENV-3 and DENV-4). Aedes aegypti and Aedes albopictus mosquitoes transmit DENV, which causes symptomatic dengue in some infected individuals and asymptomatic infection in others. Although Sri Lanka has been experiencing dengue outbreaks since 1960, the disease burden and severity has increased in the last two decades, contributing to significant morbidity and mortality in the island. Innovative strategic methods must be planned and implemented for effective dengue control, targeting dengue vectors via multiple methods. Some recent developments in vector control include the use of insecticide-treated long lasting mosquito nets, lethal ovitraps, spatial repellents, genetically modified mosquitoes and Wolbachia-infected Aedes. Some of these new methods might play an important role in the longterm prevention and control of dengue. The current review highlights the importance of pooling existing knowledge and resources to work on capacity building using all available human and financial resources to optimize the vector control programme. These efforts would facilitate and improve regional cooperation, foster networking and encourage sustainable co-ordination to retain effective control methods. Motivated staff working on vector control, prediction models such as geographic information systems (GIS) to detect future dengue outbreaks and coordination of control methods in risk areas within a country or implementing country-wide specific strategic control measures will be crucial to reduce the existing dengue burden.

Multiple dengue virus (DENV) serotypes circulating in a geographical area most often lead to simultaneous infection of two or more serotypes in a single individual. The occurrence of such concurrent infections ranges from 2.5 to 30 per cent, reaching as high as 40-50 per cent in certain dengue hyper-endemic areas. Concurrent dengue manifests itself differently than mono-infected patients, and it becomes even more important to understand the effects of co-infecting serotypes in concurrent infections to ascertain the clinical outcomes of the disease progression and transmission. In addition, there have also been reports of concurrent DENV infections in the presence of other arboviral infections. In this review, we provide a comprehensive breakdown of concurrent dengue infections globally. Furthermore, this review also touches upon the clinical presentations during those concurrent infections categorized as mild or severe forms of disease presentation. Another aspect of this review was aimed at providing insight into the concurrent dengue incidences in the presence of other arboviruses.

Objective: Dengue fever (DF) is one of the most common public health problems in Sri Lanka. A pilot study was undertaken to investigate the clinical profiles of DF and dengue haemorrhagic fever (DHF) in patients admitted to two hospitals from July 2011 to July 2012. The objective of the study was to evaluate clinical patterns to improve pattern recognition and to determine whether these profiles have changed in recent times. Study design: The clinical profile was collected using a CDC style questionnaire and analyzed (Minitab, V14). Blood samples were collected from 50 patients from Gampaha and 204 patients from Negombo hospitals with a clinical suspicion of DF/DHF, between fever days 2 to 7. Laboratory data included a complete blood count (CBC) with haemoglobin, haematocrit, total leukocyte and platelet countsand liver function. CBC was repeated daily during the acute phase of the illness. Chest x-ray or ultrasound scanning was done to assess pleural and abdominal fluid accumulation. Results: The sample consisted of 168 (66.1%) males and 86 (33.8%) females. The age of the patients ranged from 6 months to 66 years with a mean of 12 (SD = 13.4). Fever was the major presenting complaint (100%) with headache in 90.1%. Retro orbital pain was present in 27.6% of patients and 78 % and 79.1 % experienced arthralgia and myalgia respectively. Rash and pleural effusion were present in 20% and 10.6 % respectively. Ascites and hepatomegaly were noted in 6.2% and 1.1%. Of the 254 patients, 69% had DF and 31% had DHF. The lowest WBC was 0.98 x 10 3 /mL. Platelet count of <100,000 was seen in 65.3% cases. Only 35 patients (21 DF and 14 DHF) were tested for IgM/IgG. Based on these results, 38% (8/21) of DF cases were primary and 62 % (13/21) were either secondary or with past flavivirus infections. Primary dengue infection resulted in 43% (6/14) of DHF cases with 57% (8/14) resulting from secondary or with past flavivirus infections.

Background Spatial and temporal changes in the dengue incidence are associated with multiple factors, such as climate, immunity among a population against dengue viruses (DENV), circulating DENV serotypes and vertical transmission (VT) of DENV in an area at a given time. The level of VT in a specific location has epidemiological implications in terms of viral maintenance in vectors. Identification of the circulating DENV serotypes in both patients and Aedes mosquito larvae in an area may be useful for the early detection of outbreaks. We report here the results of a prospective descriptive study that was conducted to detect the levels of VT in Aedes mosquito larvae and circulating DENV serotypes in patients and Aedes mosquito larvae from December 2015 to March 2017 in an area of Sri Lanka at high risk for dengue. Methods A total of 200 patients with clinically suspected dengue who had been admitted to a tertiary care hospital during a dengue outbreak (3 study periods: December 2015–January 2016, June–August 2016, December 2016–January 2017) and in the inter-outbreak periods (February–May 2016 and September–November 2016) were investigated. Blood samples were drawn from the study participants to test for DENV. The houses of the study participants were visited within 7 days of admission to the hospital, and Aedes larvae were also collected within a radius of 400 m from the houses. The larvae were separately identified to species and then pooled according to each patient’s identification number. Patients’ sera and the Aedes larvae were tested to identify the infecting DENV serotypes using a reverse transcription PCR (RT-PCR) method. Levels of VT in Aedes mosquito larvae were also identified. Results All four DENV serotypes (DENV-1 to -4) were identified in the study area. In the early part of the study (December 2015–February 2016), DENV-3 was predominant and from April 2016 to March 2017, DENV-2 became the most predominant type. Four cases of DENV co-infections were noted during the study period in patients. Interestingly, all four DENV serotypes were detected in Aedes albopictus larvae, which was the prominent immature vectorial form identified throughout the study period in the area, showing 9.8% VT of DENV. With the exception of DENV-4, the other three DENV serotypes were identified in Aedes aegypti larvae with a VT of 8.1%. Conclusion Comparatively high rates of VT of DENV was detected in Ae. albopictus and Ae. aegypti larvae. A shift in the predominant DENV serotype with simultaneous circulation of all four DENV serotypes was identified in the study area from December 2015 to March 2017. Graphical Abstract