Summer is OFFICIALLY HERE! Unfortunately, Texas’ scorching heat welcomes our favorite pest, the mosquito. Along with their unwanted, yet expected presence, comes mosquito-transmitted infections, such as: West Nile, Zika, Chikungunya, Malaria, Dengue, etc.
I’m about to get my nerd on here … No really, I wasn’t joking. This is me when I was finishing my thesis on mosquito-transmitted infections. I was truly happy.
I’ve decided to touch on the most known and “heard about” mosquito-borne disease. Although, our first thoughts when dealing with mosquito-transmitted infections are that it’s a tropical world and third world problem. We always hear about how mosquitos cause millions of Malaria cases and deaths all over the world. However, with global warming and rising temperatures, many of the mosquito-transmitted infections that were once thought of as only in tropical climates are making its way to the United States. Some of these diseases are already here. For example, Dengue is found throughout the and widespread throughout Central and South America, Africa, Asia, and Oceania. However, Dengue outbreaks have happened in southern parts of the United States and Hawaii.
I wanted to provide a quick overview of these diseases for awareness, educational purposes and for future reference. So, let’s take a quick “bite” out of these mosquito-borne illnesses.
INTRODUCTION TO THE DENGUE VIRUS
Dengue has always been one of my favorites, if not my favorite. Dengue virus (DENV), causes a disease/condition known as “break bone”, it is an infectious febrile virus transmitted by mosquitoes, capable of causing life-threatening symptoms, and in some cases is fatal. Infection of DENV causes Dengue fever (DF) and can consecutively precede into Severe Dengue, or Dengue hemorrhagic fever (DHF), and Dengue Shock Syndrome (DSS). Dengue fever, or “Breakbone fever” acquired its nickname from the “bone-breaking” muscle aches from the infection. After transmission, the Dengue virus takes control over skin and immune cells and infects the blood stream with viral replicates. As the virus infects tissues and organs the body counters the attack with inflammation, and it causes the muscle pains. Dengue fever can progress into Severe Dengue initiating damage to platelets (they are responsible for blood clotting) in the blood and causing bleeding underneath the dermis. A more severe Dengue condition is DSS, which could lead to anaphylactic shock and death. Clinical diagnosis is imperative when trying to diagnose Dengue fever. Eighteenth-century records of Dengue fever described patients having a loss of consciousness due to the feverish condition and having to stagger around with swollen limbs. Dengue Fever can range from flu-like symptoms to the most severe dengue disease.
Symptoms of DF include:
• Muscle Aches
• Malaise (general)
• Nausea and Vomiting
• Decreased Appetite
ACUTE phase symptoms include:
• Worsening of previous symptoms
Shock-like state or DSS symptoms include:
• Cold and clammy extremities
The vector primarily responsible for Dengue virus transmission is the Aedes aegypti mosquito, which prefers to lay its eggs in artificial containers that collect rainwater and actively bite early morning after daybreak and in the afternoon before dark. A. aegypti mosquitoes may transmit the virus and feed upon several people in a short period of time, making it an effective epidemic vector. This is where it gets complicated, yet exciting!
[This is a little more in-depth, the last paragraph will provide a more straightforward summary]
In-depth Explanation [Skip to last paragraph for a summary]
Dengue virus has 4 serotypes [1-4], in which, the first infection of one of these serotypes causes primary Dengue and is not usually fatal, however, subsequent infection with one of the other serotypes can lead to Severe Dengue, which can be fatal. The initial Dengue viral infection from one of the Dengue serotypes, allows the body to produce antibodies that circulate throughout the system. The presence of a secondary Dengue infection causes the body’s antibodies from the first infection to bind incorrectly to the secondary Dengue infection retaining pathogenic activity. With pathogenic activity still intact, the virus can still bind to cell surfaces and cause infection. Antibodies bound to the second strain of Dengue cells are going to latch onto the constant part and take it inside the cell where the virus escapes and causes infection. If an individual were to be infected with the same strain of the initial Dengue virus’ antibodies it will bind and inactivate the virus so the cell recognizes to kill. The virus has two ways of entering the cell. It can enter the cell by receptors attached to the cell, as well as, allowing the virus to acquire a ride from being attached to antibodies because the antibodies presents the virus to the cells to take it up and the virus can now cause infection to additional cells. The cell may not have had a receptor for antibody; however, because it was bound to the antibody the cell has access. Antibody-dependent enhancement (ADE) events occur as antibodies against the first strain contribute to the effectivity of the second strain allowing a wider effect on cells and wider infection of disease. In the case of disseminated intravascular coagulopathy (DIC), rashes appear on the skin where blood collects under the skin; this is due to clotting and impeding blood flow. Organs start to shut down due to lack of blood flow, leading to death. Cytokine storms are also involved with a ton of interferons being produced: IFNγ, IL-12, and IL2. It is not fully understood how secondary Dengue infection predisposes people to DHF; however, antibody-dependent enhancement (ADE) and disseminated intravascular coagulopathy (DIC) are the most accepted explanation.
Summary of Second Infection
The immune system reacts normally by creating antibodies to fight the viral invaders. Those antibodies can then be confused if confronted later with one of the other three types of dengue virus. In short if you are infected with any of the Dengue virus types, there is a good chance of recovery. However, getting infected once can put people at greater risk for a more severe infection down the road. There is an interaction between a person’s immune response and a subsequent dengue infection. That could mean the difference between getting a mild fever and going into fatal circulatory failure.