Nandkumar M Kamat
Dengue is a mosquito-borne virus. It belongs to a family of viruses called Flaviviridae. Flaviviruses such as Japanese encephalitis, tick-borne encephalitis (TBE), dengue fever have found a haven in Goa. Kaisodi virus could also enter from forests of Mysore. Urbanisation has gifted Goa with mosquito-borne diseases like malaria, filaria, elephantiasis, Japanese encephalitis, chikungunya and dengue fever.
On July 20, 2015, in this newspaper I had written about KFD (caused by KFDV) and dengue (caused by DENV) outbreaks in Goa. More than 40,000 dengue cases were reported in India during 2014. The cases reached 1,29,166 in 2016, 1,88,401 in 2017, 1,01,192 in 2018, 1,57,315 in 2019 before sharply declining to just 34,419 in 2020. Goa reported 198 cases of dengue in 2013, more than 100 in 2015 and this increased to 726 in 2019 and 376 in 2020. We need to see the morbidity this year during the typical dengue (DENV) season-June-October. This is a new viral threat emerging during present pandemic and it would torment urban Goa till October if prompt measures are not taken to control the vector mosquito, the dreaded Aedes egyptii. Urban dengue is raising its ugly head once again in Vasco, Goa’s most populated town.
Mahadev, Fulmali and Mishra in 2004 had conducted a preliminary study of multilevel geographic distribution and prevalence of Aedes aegypti in the state of Goa, India. This paper was published in Indian Journal of Medical Research. They had warned that steps have to be taken to monitor and control breeding ground because A. egypti is responsible for dengue (Flaviridae: Flavivirus) viruses (DEN); yellow fever (YF: Flavivirus) and the chikungunya (CHIK: Togaviridae: Alphavirus). Water stagnation during the cyclone has benefitted the proliferation of Aedes egyptii. With favourable temperature and high humidity Aedes egyptii would rule Goa till October end. The female mosquitoes readily spot any place with stagnated water to lay eggs. So, it’s important to survey and drain stagnated water to reduce density and population of Aedes egyptii.
Government of Goa needs to follow the Integrated Vector Management (IVM) approach of WHO immediately to control the Aedes egyptii mosquito population. Fumigation drives with mosquitocidal insecticides are necessary in all major towns. If anyone has fever which reads 40 degree Celsius or 104 degree Fahrenheit and shows any two of these symptoms – severe headache, pain behind the eyes, nausea, vomiting, swollen glands, muscle and joint pains, rash, then rush to have blood test first to rule out or confirm dengue. There is no specific treatment.
Dengue, a viral disease, is an excellent indicator of bad urbanisation and poor public sanitation. Globally, dengue virus (DEN) comprises four distinct serotypes (DEN-1, DEN-2, DEN-3 and DEN-4). Goa has an impressive diversity of mosquitoes, more than 60 species, but dengue is favourite of Aedes aegypti mosquitoes which is the main vector that transmits the viruses that cause dengue. The viruses are passed on to humans through the bites of an infective female Aedes mosquito, which mainly acquires the virus while feeding on the blood of an infected person.
Dengue viruses originally were probably introduced in Goa by migrant labourers from dengue infected zones. Once infected, humans become the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes. The virus circulates in the blood of an infected person for two-seven days, at approximately the same time that the person develops a fever. Patients who are already infected with the dengue virus can transmit the infection via Aedes mosquitoes after the first symptoms appear (during four-five days; maximum 12). The only advantage if one recovers from the disease is lifelong immunity against that virus serotype. But it confers only partial and transient protection against subsequent infection by the other three serotypes of the virus. Suppose a person is infected by another serotype then it could be dangerous. So, in crowded urban Goa one can imagine how fast dengue can spread from one township or market to another.
The World Health Organisation (WHO) is worried about dengue, which is a fast-emerging pandemic-prone viral disease in many parts of the world. WHO found that dengue flourishes in urban poor areas, suburbs and the countryside and affects more affluent neighbourhoods. WHO estimates that the incidence of dengue has increased 30-fold over the last 50 years. Up to 50-100 million infections are now estimated to occur annually in over 100 endemic countries, putting almost half of the world’s population at risk.
The full life cycle of dengue fever virus involves the role of mosquito as a transmitter (or vector) and humans as the main victim and source of infection. I had claimed three years ago that Goa could have developed a new genotype, a variant of locally adapted dengue virus but that is for Goa Medical College and National institute of Virology to work on because the “Asian” genotypes of DEN-2 and DEN-3 are frequently associated with severe disease accompanying secondary dengue infections.
Without waiting for the government action people need to survey their areas for any empty container including indoor flowerpots. trays of the domestic water coolers, discarded ice cream cups and bottle crowns, coconut shells, and drain the open terraces of buildings with pools of stagnated water to prevent proliferation of Aedes egyptii and spread of dengue during this pandemic. The health department is already monitoring the situation. Henceforth it should advise all the patients in urban areas with fever to also check for presence of DENV by serological testing along with COVID-19 standard RT PCR testing.