Dengue fever
Dengue fever is a disease transmitted by mosquitoes produced by the dengue virus endemic in tropical areas. It is usually symptomless if the symptom is felt it typically begins 3 to 14 days after infection. These can include a high fever headache nausea muscle and joint aches and a distinctive skin itching and skin rash. Recovery is typically two to seven days. In a few percentage of instances. the illness becomes severe dengue formerly known as dengue hemorrhagic fever or dengue shock syndrome with bleeding low platelet level in the blood plasma leakage and critically low blood pressure.
There are four well-established serotypes of infection with dengue virus with infection with one generally confers lifelong immunity to that same type but temporary immunity to the others. Infection with a second type increases the likelihood of serious complications. Signs of dengue resemble many other conditions like malaria influenza and Zika. Blood tests can be employed to confirm the diagnosis like detecting viral RNA or virus antibodies.
Treatment of dengue fever is symptomatic as no treatment of dengue fever is known. Mild dengue is managed with pain management.
Dengue is spread by several female species of Aedes mosquitoes, mainly Aedes aegypti. Prevention of infection can be achieved by clearing mosquitoes and avoiding bites. Two dengue vaccines are licensed and commercially available. Dengvaxia was introduced in 2016, but it is recommended only for the prevention of re infection among previously infected patients. The second vaccine Qdenga has entered the market in 2022 and can be administered to adults adolescents and children up to four years of age.
Cause of dengue fever
pathology
Dengue virus is a virus in the family Flaviviridae genus Flavivirus. Other members of the same family are yellow fever virus West Nile virus and Zika virus. The genome of dengue virus consists of about 11,000 nucleotide bases. These code for three structural protein molecules forming the virus particle and seven other protein molecules which are required for replication of the virus. There are four strains of the virus known as serotypes by the names DENV-1 DENV-2 DENV-3 and DENV-4. The serotypes differ based on their antigenicity.
transferral
The virus is primarily spread by mosquito bites belonging to the genus Aedes. They bite during the night and early morning hours but they bite and infect at any time of the day. One can become infected from a single bite.
2 to 10 days after becoming newly infected a persons blood will contain a high level of virus particles. A female mosquito which has fed on the infected host then transmits the virus in the lining cells of its gut. In a matter of days the virus infects other tissues like the mosquitos saliva glands and is secreted in its saliva. On feeding again for the subsequent feed infectious saliva will be inoculated into the blood of its victim spreading the disease. The virus has no deleterious effect on the mosquito, which gets infected for life.
Dengue is also spread by infected blood products and organ donation. Mother-to-fetus vertical transmission during pregnancy or during delivery has been reported.
Risk factors of dengue fever
The primary dengue infection risk is from an infected mosquito bite. This is more probable where there is high population density, poor hygiene, and areas prone to standing water where mosquitoes can breed. It can be avoided by preventing bites through the use of clothing that is in complete contact with the skin using mosquito netting when resting or the use of insect repellent.
Chronic diseases such as asthma sickle cell anemia and diabetes mellitus increase the risk of severe disease. Female sex and higher body mass index are also risk indicators for severe disease. Infection with a single serotype is thought to provide lifelong immunity to that serotype but only transient protection against the other three. Upon re infection with another serotype the risk of serious complications is increased through a process termed antibody dependent enhancement.
In antibody dependent enhancement antibodies bind to viral particles as well as Fc gamma receptors present on immune cells increasing the chances of the viruses infecting the cells.
The exact mechanism of ADE is still not clear. It appears that ADE occurs when the antibodies produced in an immune response bind to and recognize a pathogen but fail to neutralize it. Instead, the antibody virus complex acquires greater ability to bind to the target immune cells’ Fcγ receptors so that the virus infects the cell and reproduces itself.
Prevention of dengue fever
Vector control
The principal risk of dengue infection is the bite of an infected mosquito. This is most likely where the disease is endemic especially where there is poor sanitation, high population density, and standing water in which mosquitoes can breed. It can be avoided by taking steps to avoid bites such as wearing clothing that fully covers the skin using mosquito netting when sleeping and/or the use of insect repellent. It is also advised to treat tent and clothes nets with 0.5% permethrin.
The house can also be protected by door and window screens with the use of air conditioning and by draining and cleaning every container indoors and outdoors which could hold water periodically.
The most important way of controlling A. aegypti is by eliminating its breeding sites. This is done by eliminating open water sources or if this is not possible by applying insecticides or biological control agents to these locations. Generalized spraying with organophosphate or pyrethroid insecticides and while sometimes done is not regarded as effective.
The removal of free standing water by alteration of the environment is the method of choice for control in light of the protests against negative health effects from the application of insecticides and increased logistical difficulties for control personnel. Ideally, mosquito control should be a community activity. when every member of a community cleans clogged gutters and street drains and keeps their yards clear of containers that hold standing water. If houses have direct supply of water this stops the use of wells or street pumps and water carrying containers.
Vaccine for fever
Subcutaneous injection
Dengvaxia was approved in 2015 and is approved for use in the US EU and some Asian and Latin American countries. It is an attenuated virus which is suitable for individuals in the age group of 6 45 years and it confers immunity to all four serotypes of dengue. It must be given only to those who have previously been infected with dengue, to immunize them against subsequent reinfection. It is given subcutaneously in three doses spaced six months apart.
It has been licensed by various other countries like Indonesia and Brazil and has been recommended by the SAGE committee of the World Health Organization.