Epidemiology And Demographic Factors Of Dengue In Rural Area Of Indian Union Territory, Puducherry
Abstract: Background: Dengue Fever (DF) is caused by dengue virus (DENV) which is transmitted by the bite of Aedes aegypti mosquito. Incidence of DF is more prevalent in tropical and subtropical areas of the world. This hospital based study is a surveillance data on the prevalence of DF among the rural population of Puducherry, India.Materials and Methods: Patients admitted to the hospital with the probable diagnosis of DF were included in the study irrespective of age and sex. A total of 1880 patients were screened for DF by NS1 antigen, IgM using ELISA test and IgG antibody by rapid card test during the period of January 2017 to February 2018 and a month wise incidence was recorded including age and sex.Results: Out of 1880 patients, 607(32.2%) were positive for DF of which 353(18.8%) were men. The age group of 21-30 was the most commonly affected (9.57%) followed by 31-40 age group (6.48%). A total of 293(48.2%) cases were found to be positive for NS1 antigen detection alone whereas 137 (22.5%) and 18(2.9%) for IgM and IgG respectively. A peak in the incidence rate was observed during the month of October (N=256) followed by September (N=124) and is least in January and February (N=5).Conclusion: About 32.2% of total cases were positive for DF serology, which is a remarkable increase when compared to the previous study in this region. The increased rate of infection in men and in active working age group of the study shows that outdoor activities may be associated with so high risk for acquisition of DF. Vector control measures and awareness campaigns explaining the nature of the disease and preventive measures can be helpful in lowering the rate of infection.
Key words: Dengue Fever Dengue, Severe Dengue, NS1 protein.
Dengue fever (DF) is the most common and considerable arthropod-borne viral (arboviral) illness in humans, transmitted by mosquitoes of the genus Aedes, which are widely distributed in subtropical and tropical areas of the world. The increasing trend in the incidence of dengue in the recent decades shows that an estimate of 40%-50% of the world’s population, with a major proportion from the tropical, subtropical and more temperate areas are at the risk of DF. When diagnosed early and provided with proper medical care, the mortality rate associated with DF is as less as 1%. The mortality rate of severe dengue when treated is 2%-5%, and is as high as 20% when left untreated. Symptoms like high fever (104°F/40°C), retro-orbital pain, muscle and joint pain, nausea, lymphadenopathy, vomiting, and rash leads to a possible DF. People who have travelled within 2 weeks of symptom onset to an area where appropriate vectors are present and dengue transmission may be occurring can be suspected for DF and subjected to diagnosis.
Dengue Virus (DENV) is a single stranded RNA virus belonging to the family Flaviviridae, genus Flavivirus which also includes West Nile virus, Tick-borne Encephalitis Virus, Yellow Fever Virus, and several other viruses which may cause encephalitis. The disease caused by DENV can be a self limited Dengue Fever (DF) or a life-threatening syndrome called Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS).
The genome of the virus is composed 11000 bases that encodes a single large polyprotein that is subsequently cleaved into into three structural proteins, namely, C, prM, E and seven nonstructural proteins, NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5. The genome is short non-coding regions on both the 5′ and 3′ end.
The preliminary diagnosis of DF relies on a combination of travel history and clinical symptoms since laboratory-based diagnosis is often unavailable at the time of care. There are however, limitations with each test, and detection is based on different virological markers, namely, viral RNA (vRNA), and DENV-specific antibodies.
Few alternative methods based on the detection of the viral NS1 protein have been developed due to the drawbacks of serological methods to reliably diagnose acute infections. During acute dengue infection when IgM is not detectable, NS1-based ELISA is considered as an important diagnostic tool where PCR (Polymerase Chain Reaction) is not available. In endemic as well as non-endemic countries there are several commercial NS1 antigen kits are available for the diagnosis purposes. Based on the time following infection that the test is performed, DENV serotype and whether it is a primary or secondary DENV infection, the sensitivity varies from 63% to 94% [1,2,3,4].
Apart from the increase in the number of cases, disease spread to new areas, and explosive outbreaks are also occurring. Therefore, the objectives of this study were to study the epidemiological and demographic factors of DF in a rural area of Puducherry to improve the localized dengue surveillance and early warning system.
Materials and Methods:
This is a hospital based retrospective study, carried out at the Department of Microbiology, Sri Manakula Vinayagar Medical College and Hospital, a tertiary care hospital, at Puducherry. patients admitted to the wards with clinically suspected dengue/DHF/DSS with manifestations like headache, retro orbital pain, myalgia, arthralgia, rash, hemorrhagic manifestations, and leucopenia as described by World Health Organization (WHO)  were included in the study. A total no of 1880 patients were screened for dengue by NS1 antigen, IgM and IgG antibodies during the period of January 2017 to February 2018. NS1 antigen (INBIOS) and IgM (J mithra) detection was done by enzyme linked immunosorbent assay (ELISA) as per the manufacturer’s protocol. IgG antibody was detected by rapid card test method. Patients irrespective of all ages from puducherry and the neighboring districts were included in this study.
Of the 1880 samples, 607(32.2%) were positive for dengue serology. Among the 607(32.2%) positive cases 353 (18.8%) were male and 254 (13.5%) were female (Figure 1). The age group of 21-30 was the most commonly affected group (9.57%) followed by 31-40 age group (6.48%) (Figure 2). In the month of October, 256 cases were diagnosed with DF, which is the highest rate registered per month, followed by September (124 cases) (Figure 3). 293(48.2%) cases were found to be positive for NS1 alone whereas 137 (22.5%) and 18(2.9%) for IgM and IgG respectively. Both positive cases ie, NS1 and IgM positive were 122(20%), NS1 and IgG were 5(0.8%), IgM and IgG were 14(2.3%) and all three tests positive cases were found to be 18(2.9%)
In the recent decades the incidence of dengue is found to be increasing all over the world. The actual number of cases are under reported due to misclassification of dengue. It is recently estimated that 390 million dengue infections occur per year (95% credible interval 284–528 million), of which 96 million (67–136 million) manifest clinically . In 2012, brady et al., reported that an estimate of 3.9 billion people, in 128 countries, are at risk of infection with dengue viruses . Our study from the month of January 2017 to February 2018 showed that there was an increase in the infection rate month wise. In our previous study, in the same rural tertiary care hospital, the prevalence rate observed was 13.9 % . Our current study showed 32.2% which is more than as two fold increase in the prevalence of dengue compared with previous study. Majority of the people attending this hospital are from a rural areas where there is a lack of proper sanitation and drainage systems, and the habitats are near water logging or stagnant areas that are favorable for mosquitoes breeding, which may be the reason for this high prevalence rate.
Studies conducted in Brazil, Singapore, India and Saudi Arabia showed that dengue mostly affect adults in the age group of 21–70 years old [9,10,11,12]. In our study also, adults of age 21-40 years [302/607 (49.7%) cases] were more susceptible to dengue infection. More outdoor activities in the adult groups (> 20 years old) increases the probability of being exposed to infected mosquitoes than the younger age group (< 18 years old). A male preponderance reported in studies from Cambodia, Malaysia, Sri Lanka, Singapore, Philippines and India suggests that men has more common outdoor work habits which gave them more chances to be bitten by mosquitoes than females [13,14]. On the other hand, there were gender differences in infection with different DV serotypes that were probably due to different pathogenic processes or immune responses. Our current study and previous study showed the highest rate of infection during the month of September and October which is the end of monsoon and beginning of post monsoon period in this region (8). It was also noted that number of positive cases started increasing from monsoon season to post monsoon season, because that season is considered as favorable for breeding of the vector, i.e., Aedes aegypti. Many dengue cases were reported during the post monsoon season, i.e., from September to November in various studies reported in India [15,16].
Among the 607 positive cases, 293(48.2%) were NS1-positive patients (Figure 4) which clearly indicates they were suffering from a primary infection and in the early phase of illness and were also viremic, i.e. they could transmit the virus if bitten by a mosquito. 137 (22.5%) patients were found to be only IgM positive cases which represents as recent primary infection presenting at a later phase of infection. The 18 (2.9%) patients with only IgG positive showed that patients had dengue for the second or third time (i.e., recent secondary or tertiary infections, which were indistinctly referred to as recent secondary infections). The IgG positivity may be due to subsequent infection with dengue serotypes 1/ 2/ 3 or 4 during the preceding outbreaks and this may have sensitized them to the tests . They could have been infectious for mosquitoes during the earlier phase of illness. In this study the reinforcement of utility of antigen detection during the earlier phase of illness was indicated by NS1-positive and IgM-positive concurrency that was found in 122 (20%) patients (Figure 4). Both NS1 and IgG positive pattern were observed in 5 (0.8%) patients, which denotes the secondary viral infection and such a type of infection pattern would have also been overlooked. they would have been labeled as “dengue negative” without NS1 screening . 14(2.3%) cases had presented in a later stage of illness with a recent primary or secondary infection by showing positive for both IgM and IgG (Figure 2). NS1, IgM and IgG (triple-positives) were found in 18 (2.9%) patients[Figure 4]. These triple positives were considered as at the late stage of either a primary or a secondary infection and might have been infectious for mosquitoes.
Dengue infections commenced from the month of July, reached as peak in September and decreasing from November onwards. Environmental factors such as rain, temperature and relative humidity have favored the dengue infections. Young adults and males are more susceptible to dengue infection. ELISA and rapid test for dengue has enhanced our ability to detect new infections and to characterize them into primary and secondary infections, permitting the estimation of the minimal attack rate for a population during an outbreak. The rise in the incidence of dengue indicates the probable lack of adequate vector control measures. Social awareness, personal protection and vector control measures to prevent the spread is the sole weapon to fight the dengue epidemic. Improving the rapid diagnostic tools, appropriate early treatment and availability of effective vaccine against dengue may pave way to completely eradicate the dreadful DF.