[ Dr PJ Sarma ]
“Dengue is one of the fastest emerging infections and is currently the most rapidly spreading mosquito-borne known viral disease” – World Health Organisation (WHO).
Awareness generation regarding this disease is very important. For that, National Dengue Day is observed on 16 May and the month of July is observed as Anti-Dengue Month in India. This dengue prevention campaign aims to sensitise and mobilise community to take immediate action to reduce eruption of dengue cases by highlighting the health consequences of dengue and areas that are at higher risk.
The theme of this 8th National Dengue Day is ‘Harness partnership to defeat dengue’. In 2012, epidemiological studies of India indicated that Tirunelveli in Tamil Nadu was the epicentre of the dengue epidemic. Since then, Arunachal Pradesh is experiencing its epicentre in Pasighat township. During Covid-19 period, least cases were recorded, may be due to almost restricted movement of community/infected carrier or sufferer/fever screening of outsiders at entry gate of district/state.
During 2022, imported cases were detected in our state capital that arrived here from Uganda and some other parts of our country like Bangaluru, Mumbai, etc. A small outbreak was also reported in East Kameng in the end part of the year (post monsoon).
Once in a densely populated colony in Pasighat, people were facing shortage of water as the lone hand pump in the colony was drawing poor quality water (that pump was marked red and put under lock and chain). The residents of the locality then began to store water in different small and large pots without proper cover for long periods of time. There was also a tyre shop nearby the same colony, wherein old and used tyres collected rainwater for days. All these led to the spread of dengue in that area.
Dengue is an endemic disease and one of the major public health problems in India. During the last five years, the National Vector Borne Disease Control Programme (NVBDCP), now renamed NCVBDC, reported approximately 80,725 cases of dengue per year with a fatality rate of about 0.24 percent in India. According to the WHO, dengue affects approximately 100-400 million people every year. As per a scientific estimation, the global burden of dengue has increased at least fourfold over the last three decades and 2.5 billion people are now at risk of the disease. An estimated 99 million (95 percent credible interval 71-137 million) symptomatic dengue infections and 404 million asymptomatic (95 percent credible interval 304-537 million) infections occur annually in over 100 countries, with 5,00,?000 cases of severe dengue and 20,?000 deaths. There is an estimated 9 billion dollar direct and indirect medical cost of dengue in the world.
Dengue virus strains are of four distinct serotypes – DEN-1, DEN-2, DEN-3 and DEN-4. Each of them has multiple genotypes. The genotype variation can be subtle either in DNA material or the envelope. For example, DENV-1 comes in as many as five genotypes – Asia, South Pacific, Thailand, Malaysia and AM/AF. Type I causes classic dengue fever, Type II leads to haemorrhagic fever with shock, Dengue III causes fever without shock, and Dengue IV causes fever without shock or profound shock. Mixed serotype may be dangerous.
Dengue is a viral fever which transmits to humans after the bite of an infected female mosquito of the species Aedes aegypti/Aedes albopictus with a habit of day biting. The incubation period of dengue is usually from 4 to 10 days. Dengue virus (of Flaviviridae family) infections can manifest as a wide clinical spectrum of disease, ranging from ‘dengue fever’ (a self limiting mild febrile illness) to ‘severe dengue’ (dengue hemorrhagic fever, which is characterised by capillary leakage leading to hypovolaemic shock, organ impairment and bleeding complications). However, most infections remain asymptomatic or cause a relatively mild systemic illness. A few studies suggest that maternal dengue infection (materno-fetal transmission, congenital dengue viral infection) during pregnancy might increase the risk of preterm birth and low birth-weight. Neonates with congenital dengue have had clinical manifestations ranging from fever with thrombocytopenia to pleural effusions, severe haemorrhage and shock.
The clinical management relies on judicious fluid replacement of the severe cases and management of the symptoms through mild pain killers and anti-inflammatory drugs. But advice of a qualified doctor is must. Though some dengue vaccines are entering Phase III clinical trials, but none is available commercially at this time to be used by community.
Currently, there is neither any specific cure by any medicine nor any vaccine available for dengue. So, to minimise the risk of its transmission, the prevention and control of dengue is must. The strategy of its prevention and control rotates around the locus of vector control. (While doing this, it also reduces the transmission of Zika and Chikungunya.) Line departments need to work together for it and community should participate.
From public health point of view, higher dengue risk locations are about three to ten times more likely to develop into large dengue clusters, compared to areas with lower mosquito populations of Aedes aegypti.
The National Environment Agency of Singapore, promoting the concept of ‘B-L-O-C-K’ steps for control of Dengue: Break up hardened soil/Lift and empty flowerpot plates/Overturn pails and wipe their rims/Change water in vases/Keep roof gutters clear and place Bti insecticide inside.
Eleven controlling steps
Based on earlier experience, persistently high Aedes aegypti mosquito population, number of dengue cases and active dengue clusters to be detected before traditional peak dengue season (from June to October) comes.
We need intensive and concerted cohesive community effort to search for and remove stagnant water over a 14-day period, starting from pre-monsoon. The effort will cover two mosquito breeding cycles in frequent interval, helping to reduce the mosquito population/risk of dengue. Need to educate community on common mosquito breeding habitats, ground outreach effort to conduct house visits at dengue cluster areas and areas with high Aedes aegypti mosquito population (with technical input from right authority and lined departments), share dengue prevention skills and thus sustain a high level of awareness and source reduction of mosquito breeding spots to be carried out.
Weekly once compulsory removal of accumulated water from coolers and other small containers (plastic containers, buckets, used automobile tyres, water coolers, AC equipments of home etc, pet watering containers and flower vases). Need to continue checks at construction sites, and other uncovered mosquito breeding habitats like raw rubber latex collection bowl of rubber plantation, uncovered water tank of buildings.
Water storage containers should be covered with lids at all times. Wear full sleeve clothes, covering their skin in the transmission (rainy) season. Use a mosquito net or mosquito repellent while sleeping during the day. Use aerosol during the day to prevent yourself from mosquito bites.
Scientific entomological study
Modern technology of smart mobile phone provides scope through innovative app to set alerts on areas with dengue clusters and high Aedes aegypti mosquito population. Community can easily receive these push notifications if they pre-set the location on such app.
Genetically engineered mosquitoes
Next generation of infected mosquito of dengue can spread dengue as all larvae of such infected mosquito carries germs of dengue. To break this chain, during 2021, with a view to suppressing populations of wild Aedes aegypti mosquitoes (which can carry diseases like zika, dengue, chikungunya and yellow fever) genetically engineered mosquitoes (working on Endosymbiont principle) were released into the environment/air in Florida Keys of the United States. The small-scale field trials of genetically engineered cross-bred carrying Aedes aegypti mosquitoes are already performed in Australia, Brazil, Columbia, Indonesia and Vietnam, whereas large-scale field trials (citywide) performed in Yogyakarta city (Indonesia), Rio de Janeiro (Brazil) and Medellín (Colombia). Success was in a range of 70 percednt-95 percent. ICMR-VCRC (Puducherry, India) is also working on it, but it has to go through some procedures like regulatory approval that takes time regarding screening the biosafety of such technology, etc. It may bring success against chikungunya and zika virus also.
For future study, the genome sequence of the virus collected from the samples to be compared against the GenBank library which hosts all known dengue virus samples since 1943 to present time. (The writer is working in the field of public health and has experience in two developing countries.)
