aedes aegypti

Hi everyone! This Dr. Mahtab here, am writing on Dengue Fever, it’s recent types in Bangladesh and some future suspects of Dengue outbreak in Bangladesh.

What is Dengue?

According to WHO, Dengue is a mosquito-borne viral infection causing a severe flu-like illness and, sometimes causing a potentially lethal complication called severe dengue. 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.

Severe dengue (previously known as dengue haemorrhagic fever) was first recognized in the 1950s during dengue epidemics in the Philippines and Thailand. Today it affects Asian and Latin American countries and has become a leading cause of hospitalization and death among children and adults in these regions.

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.

The virus

The dengue virus (DEN) comprises four distinct serotypes (DEN-1, DEN-2, DEN-3 and DEN-4) which belong to the genus Flavivirus, family Flaviviridae.

Distinct genotypes have been identified within each serotype, highlighting the extensive genetic variability of the dengue serotypes. Among them, “Asian” genotypes of DEN-2 and DEN-3 are frequently associated with severe disease accompanying secondary dengue infections.

The mosquito

The Aedes aegypti mosquito 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.

Within the mosquito, the virus infects the mosquito mid-gut and subsequently spreads to the salivary glands over a period of 8-12 days. After this incubation period, the virus can be transmitted to humans during subsequent probing or feeding. The immature stages are found in water-filled habitats, mostly in artificial containers closely associated with human dwellings and often indoors.

Flight range studies suggest that most female Ae. aegypti may spend their lifetime in or around the houses where they emerge as adults and they usually fly an average of 400 metres. This means that people, rather than mosquitoes, rapidly move the virus within and between communities and places.

Dengue infection rates are higher outdoors and during daytime, when these mosquitoes (Stegomyia) bite most frequently. However, Ae. aegypti breed indoors and are capable of biting anyone throughout the day. The indoor habitat is less susceptible to climatic variations and increases the mosquitoes’ longevity.

Dengue outbreaks have also been attributed to Aedes albopictusAedes polynesiensis and several species of the Aedes scutellaris complex. Each of these species has a particular ecology, behaviour and geographical distribution.

Ae. albopictus is primarily a forest species that has become adapted to rural, suburban and urban human environments. In recent decades Aedes albopictus has spread from Asia to Africa, the Americas and Europe, notably aided by the international trade in used tyres in which eggs are deposited when they contain rainwater. The eggs can withstand very dry conditions (desiccation) and remain viable for many months in the absence of water and the European strain of Aedes albopictus can undergo a period of reduced development (diapause) during the winter months.

The human

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 2-7 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 4-5 days; maximum 12).

In humans recovery from infection by one dengue virus provides lifelong immunity against that particular virus serotype. However, this immunity confers only partial and transient protection against subsequent infection by the other three serotypes of the virus. Evidence points to the fact that sequential infection increases the risk of developing severe dengue. The time interval between infections and the particular viral sequence of infections may also be of importance.

Symptoms

A person infected by the dengue virus develops severe flu-like symptoms. The disease, also called ‘break-bone’ fever affects infants, children and adults alike and could be fatal. The clinical features of dengue fever vary according to the age of the patient.

Individuals should suspect dengue when a high fever (40°C/ 104°F) is accompanied by two of the following symptoms:

  • Severe headache
  • Pain behind the eyes
  • Nausea, Vomiting
  • Swollen glands
  • Muscle and joint pains
  • Rash

Symptoms usually last for 2-7 days, after an incubation period of 4-10 days after the bite from an infected mosquito.

Severe dengue is a potentially deadly complication due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment. The warning signs to look out for occur 3-7 days after the first symptoms in conjunction with a decrease in temperature (below 38°C/ 100°F) include:

  • Severe abdominal pain
  • Persistent vomiting
  • Rapid breathing
  • Bleeding gums
  • Blood in vomit
  • Fatigue, restlessness

The next 24-48 hours of the critical stage can be lethal; proper medical care is needed to avoid complications and risk of death.

Treatment

There is no specific treatment for dengue fever.

Patients should seek medical advice, rest and drink plenty of fluids. Paracetamol can be taken to bring down fever and reduce joint pains. However, aspirin or ibuprofen should not be taken since they can increase the risk of bleeding.

For severe dengue, medical care by physicians and nurses experienced with the effects and progression of the disease can frequently save lives. Maintenance of the patient’s circulating fluid volume is the central feature of such care.

Prevention and control

The only current method of controlling or preventing dengue virus transmission is to effectively combat the vector mosquitoes.

Vector control

Preventing or reducing dengue virus transmission depends entirely in controlling the mosquito vectors or interruption of human–vector contact. WHO promotes the strategic approach known as Integrated Vector Management (IVM) to control mosquito vectors, including those of dengue.

IVM is defined as a ‘rational decision-making process for the optimal use of resources for vector control.” The aims are to improve efficacy, cost effectiveness, ecological soundness and sustainability.

Transmission control activities should target Ae. aegypti (or any of the other vectors depending on the evidence of transmission) in its immature (egg, larva, and pupa) and adult stages in the household and immediate vicinity. This includes other settings where human–vector contact occurs, such as schools, hospitals and workplaces.

Methods of vector control

Ae. aegypti uses a wide range of confined larval habitats, both man-made and natural.

Some man-made container habitats produce large numbers of adult mosquitoes, whereas others are less productive. Consequently, control efforts should target the habitats that are most productive and hence epidemiologically more important rather than all types of container, especially when there are major resource constraints.

Vector transmission is reduced through the use or combination of these three methods:

  • Environmental management
  • Chemical control
  • Biological control

Individual and household protection

Self-initiative for source reduction in homes and community. Clothing that minimizes skin exposure during daylight hours when mosquitoes are most active affords some protection from the bites of dengue vectors and is encouraged particularly during outbreaks.

Repellents may be applied to exposed skin or to clothing. The use of repellents must be in strict accordance with label instructions.

Insecticide-treated mosquito nets afford good protection for those who sleep during the day (e.g. infants, the bedridden and night-shift workers).

Where indoor biting occurs, household insecticide aerosol products, mosquito coils or other insecticide vaporizers may also reduce biting activity.

Household fixtures such as window and door screens and air-conditioning can also reduce biting.

Safe use of insecticides

All pesticides are toxic to some degree. Safety precautions for their use – including care in the handling of pesticides, safe work practices for those who apply them, and appropriate field application – should be followed.

WHO Pesticide Evaluation Scheme (WHOPES) has published specific guidelines on use of insecticides, safety procedures, quality control and guidelines for testing.

Vector control is implemented using Integrated Vector Management (IVM) approach, which is a rational decision-making process for the optimal use of resources for vector control.

IVM requires a management approach that improves the efficacy, cost-effectiveness, ecological soundness and sustainability of vector control interventions given the available tools and resources.

Proper solid waste disposal and improved water storage practices, including covering containers to prevent access by egg-laying female mosquitoes are among methods that are encouraged through community-based programmes.

IVM is a rational decision-making process for the optimal use of resources for vector control. The approach seeks to improve the efficacy, cost-effectiveness, ecological soundness and sustainability of disease-vector control. The ultimate goal is to prevent the transmission of vector-borne diseases such as malaria, dengue, Japanese encephalitis, leishmaniasis, schistosomiasis and Chagas disease.

Rationale

Driving forces behind a growing interest in IVM include the need to overcome challenges experienced with conventional single-intervention approaches to vector control as well as recent opportunities for promoting multi-sectoral approaches to human health.

Operational strategy

The Global Strategic Framework for IVM notes that IVM requires the establishment of principles, decision-making criteria and procedures, together with timeframes and targets. The Framework identifies the following as five key elements for the successful implementation of IVM:

  • Advocacy, social mobilization, regulatory control for public health and empowerment of communities.
  • Collaboration within the health sector and with other sectors through the optimal use of resources, planning, monitoring and decision-making.
  • Integration of non-chemical and chemical vector control methods, and integration with other disease control measures.
  • Evidence-based decision making guided by operational research and entomological and epidemiological surveillance and evaluation.
  • Development of adequate human resources, training and career structures at national and local level to promote capacity building and manage IVM programmes.

In recent days until 6th August 2019, according to DGHS, around 27,437 dengue patients were admitted to different hospital across the country. Dengue cases are increasing across the country as around 2,065 more new patients were hospitalized with the mosquito-borne deadly virus in the last 24 hours till 8:00 am on Monday. Though the DGHS have been saying for the last two days that a total of 18 people, who infected with the dengue fever since January 1, have died, but the hospital sources put the death toll as high as 60. As per the media reports, at least 11 dengue patients have died since August 3.

But I think during the holy Eid -Ul-Adha, many people will come from Dhaka to their hometown for celebrating the holy occasion. Since, the vector is available in the peripheral part of Bangladesh. Those Aedes Aegypti mosquitoes don’t have the virus until they bite infected hosts. So, there is a big chance of spreading Dengue fever around the country within this time.

I suggest you all to use mosquito repellent cream and clean the surroundings to stay safe from Dengue Fever. Please, perform “NS1 antibody for Dengue virus” test within the 3rd day of any fever episode. But 3 days have passed, you may perform “ICT test for Dengue Virus Antibody” for confirmation. If infected, please, use mosquito net and  check your “Platelet count” and “PCV/HCT” at least one day interval.

I wish you all be safe from dengue fever.

Peace.

Courtesy:

WHO Website:

  1. https://www.who.int/denguecontrol/control_strategies/en/
  2. https://www.who.int/neglected_diseases/vector_ecology/ivm_concept/en/
  3. https://www.who.int/denguecontrol/disease/en/
  4. https://www.who.int/denguecontrol/mosquito/en/
  5. https://www.who.int/denguecontrol/human/en/
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