2017 has been a record year for processing U.S. passport applications. It has also been a big year for mosquitoes. As U.S. tourists travel globally, mosquito-borne illnesses such as a Zika, Malaria and Den­gue are relevant health concerns that should be considered. I recently visited Sri Lanka, a small island nation in South Asia just hanging off the southern tip of India. Starting late last year, an outbreak of Dengue has progressed, reaching epic proportions, affecting over 80,000 individuals and killing 215 in just under ten months (www.who.int/csr/don/19-july- 2017-dengue-sri-lanka/en/). I spoke with several people who shared their stories of family members and friends that contracted Dengue, and learned about current approaches to the diagnosis, treatment and patient care of people afflicted with this disease. The principal of a prominent girl’s school in Colombo with over 3000 students shared that one student and four parents of students had died of the illness, affecting their families and unsettling their communities.

2016-2017 has had the highest recorded number of cases of Dengue in the past 8 years of available data (Figure 1) with the June-Au­gust 2017 time frame topping it with almost 10,000 cases.

Colombo is the biggest city in the country. It is highly western­ized and has well developed access to water and public sewer systems. A high population of 5.6 million and a tropical climate, still bodies of water, clogged waterways, and an abundance of liter, all contribute to support the mosquito life cycle, allowing dengue to spread throughout the city.

Figure 1. Dengue Cases in Sri Lanka 2010-2017. Source: epid.gov.lk (note that data is still coming in for each week, even 3 months after it ends)

Mosquito Life Cycle

The mosquito life cycle begins with a mosquito egg hatching when it is exposed to water. The larvae emerge and enter the water, living there while molting several times until they form pupae. The pupa does not feed until it emerges as an adult mosquito which is capable of flying as soon as the outer part of its body hardens. Aedes aegypti, as described has an aquatic phase and a terrestrial phase where the total time to complete the life cycle is between 8 and 10 days.

Figure 2. Mosquito Life Cycle. Source http://www.cdc.gov

Causes/infection with dengue

According to the World Health Organization, dengue is a disease caused by a group of single stranded RNA viruses, of which five different types (serotypes) have been identified (DENV1, DENV2, DENV3, DENV4, and DENV5) (Normile, 2013). The most common form of transmission is through an infected Aedes aegypti or Aedes albopictus female mosquito, which gets its virus from an infected human. The virus enters the human bloodstream through a mosquito bite. The first time a person is infected with dengue, the virus stays in the human body and can be transferred to another mosquito through another mosquito bite un­til immunity is gained or death occurs. However, if a person with immunity to one type of dengue virus gets infected with another version of the virus, the infection is much deadlier. Most of the deaths from dengue are due to these secondary infections. The dengue virus is one of several in the flavivirus family that cause Dengue, West Nile Disease, Zika, yellow fever and chikungunya (Amaku et. al. 2011).

Course of illness

According to World Health Organization (WHO), Dengue symp­toms show up 4-10 days after the initial bite and last from 2-7 days. A fe­ver with a temperature more than 104° F, a severe headache, pain behind the eyes, nausea, swollen glands, muscle and joint pains, and rashes are common symptoms of dengue. If a case of dengue becomes severe, an advanced version comes with a reduction in temperature (no to low fever) and increase in the severity of other symptoms. This form is deadly and results in fluid from blood vessels accumulating elsewhere, resulting in the choking of the victim with fluid in the lungs, dehydradration, or organ failure.

Treatments and prevention

General recommendations from the WHO, Centers for Disease Controls and Prevention (CDC), the Environmental Protection Agency (EPA) and dozens of global agencies fighting mosquito-borne illnesses rely on prevention as their number one strategy. Prevention-based strat­egies include targeting mosquito breeding groups, prevention of attack, treating the virus vs. increasing immune response, treating the symptoms and in a few countries administering a vaccine against the virus.

Papaya Leaf Extract

Many viral illnesses are treated with nutrition, rest and general improvement of the wellbeing of the patient. In serious illnesses such as those caused by a flavivirus, shortening the duration of the illness is criti­cal to aid in patient recovery. One of the methods highlighted by ayurve­dic physicians in Sri Lanka and practitioners of natural medicine includes the use of papaya leaf extract from fresh papaya leaves and stems and consumed by the patient for several days in 1 tablespoon size doses. While the extract has little scientific research to support or disprove its efficacy, patient success in rapidly improving platelet counts appears to be extremely positive, thereby supporting the immune response to illness. A study by Abbasi et al. supports this marked improvement in patients, although it points out the need for more clinical data.

Future Research

Other advancements in the treatment of dengue are needed. The use of treatments such as the papaya leaf extract treatment needs to be tested well and introduced in areas afflicted by dengue. There are also vaccines that have not been approved for use in many areas of the world that have the potential for broader use. Currently, the vaccine is primarily available in Mexico, the Philippines, Brazil, El Salvador, Costa Rica, Paraguay, Guatemala, Peru, Indonesia, Thailand, and Singapore. The approach used for HIV viral treatment has also been shown to have potential success against the DENV virus family. However, vaccines aren’t the only solution, as mosquito control, antiviral medications and mosquito bite prevention techniques are all are valuable strategies in our fight against Dengue. Perhaps considering the CRISPR-based approach to mosquito control could be studied in Dengue carrying mosquitoes as an advanced means of control by genetic means.

Cases of dengue are managed based on the severity of the patient’s illness, the age and immune status of the patient. CDC’s case management guidelines are similar to those practiced in Sri Lanka except for the very large of number of patients affected by this epidemic which is stressing the healthcare system, lack of hospital staff and care facilities leaving serious patients with a shortage of medical care.

Recommendations for Control of Dengue (and Other Mosquito-borne Illnesses)

In many parts of the world, mosquito control is fundamental and takes the form of chemical application by spraying, fumigation, burning leaves and herbs or using nets. These are all generally good methods and relatively low cost approach to prevention that needes to be contin­ued. Another method that has value is to prevent the re-introduction of mosquitoes into areas which had been cleared or eliminate standing wa­ter deposits. Additionally, preventing a Dengue patient from being bitten by another mosquito is a critical step in preventing the cycle from being completed. Sequestering patients is often difficult to do when there is an epidemic of patients in countries with limited medical facilities, but some approach must be taken to deal with this issue. Novel approaches to treatment such as ayurvedic and plant extracts should also be seriously considered and funded to identify potential immunotherapies. In Buddhist countries like Sri Lanka, it is also a challenge to implement mosquito eliminating strategies when segments of the population believe in a no kill approach to all life forms, includes those of mosquitoes and other vectors of human illness. Educating the population is thus a critical step in the success of mosquito control.

Figure 3. Recommendations for Control of Mosquito-borne Illnesses

Controlled Kill at Harborage Sites

During the egg phase, Aedes can survive a moisture free-state (desiccation) for months, which makes mosquito control a challenge. A concerted effort to eradicate mosquitoes can be made by facilitating the mosquitoes in laying their eggs in monitored containers of water which will be dried out, water used to wet a plant or directly poured onto the ground in a manner that does not feed a stream, or create a reservoir. This is a controlled kill of the mosquito larvae by separating it from the water it needs to complete its life cycle. Although this approach is a very low cost strategy, unless executed with a timed, observant precision it bears some risks. However, the potential impact on mosquito populations could be significant from the execution of a carefully thought out plan of action, education and communication with the help of the public to fight the cycle illness from mosquitoes.

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