Dengue

Blood

Blood accounts for 7% of the human body weight,^[3][4] with an average density of approximately 1060 kg/m³, very close to pure water's density of 1000 kg/m³.^[5] The average adult has a blood volume of roughly 5 litres (11 US pt),^[4] which is composed of plasma and several kinds of cells. These blood cells (which are also called corpuscles or "formed elements") consist of erythrocytes (red blood cells, RBCs), leukocytes (white blood cells), and thrombocytes (platelets). By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.

Platelet

Platelets, also called thrombocytes, are a component of blood whose function (along with the coagulation factors) is to stop bleeding by clumping and clotting blood vessel injuries.

The main function of platelets is to contribute to hemostasis: the process of stopping bleeding at the site of interrupted endothelium. They gather at the site and unless the interruption is physically too large, they plug the hole. First, platelets attach to substances outside the interrupted endothelium: adhesion. Second, they change shape, turn on receptors and secrete chemical messengers: activation. Third, they connect to each other through receptor bridges: aggregation.^[7] Formation of this platelet plug (primary hemostasis) is associated with activation of the coagulation cascade with resultant fibrin deposition and linking (secondary hemostasis). These processes may overlap: the spectrum is from a predominantly platelet plug, or "white clot" to a predominantly fibrin clot, or "red clot" or the more typical mixture. The final result is the clot. Some would add the subsequent clot retraction and platelet inhibition as fourth and fifth steps to the completion of the process^[8] and still others a sixth step wound repair.

Low platelet concentration is thrombocytopenia and is due to either decreased production or increased destruction. Elevated platelet concentration is thrombocytosis and is either congenital, reactive (to cytokines), or due to unregulated production: one of the myeloprolerative neoplasms or certain other myeloid neoplasms. A disorder of platelet function is a thrombocytopathy.

Platelet concentration is measured either manually using a hemocytometer, or by placing blood in an automated platelet analyzer using electrical impedance, such as a Coulter counter.^[21] The normal range (99% of population analyzed) for platelets in healthy Caucasians is 150,000 to 400,000 per cubic millimeter ^[22] (a mm³ equals a microliter). or 150–400 × 10⁹ per liter.

Dengue

Dengue fever, also known as breakbone fever, is a mosquito-borne tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles. In a small proportion of cases, the disease develops into the life-threatening dengue hemorrhagic fever, resulting in bleeding, low levels of blood platelets and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs.

Dengue virus infects cells of the human immune system, leading to symptoms that include liver damage and loss of white blood cells. In severe cases, blood plasma leaks out of the circulatory system and collects in body cavities, which can be fatal.

Dengue virus is primarily transmitted by Aedes mosquitoes, particularly A. aegypti.[4] They typically bite during the day, particularly in the early morning and in the evening,[19][20] but they are able to bite and thus spread infection at any time of day all during the year.[21]

A female mosquito that takes a blood meal from a person infected with dengue fever, during the initial 2–10 day febrile period, becomes itself infected with the virus in the cells lining its gut.[24] About 8–10 days later, the virus spreads to other tissues including the mosquito's salivary glands and is subsequently released into its saliva. The virus seems to have no detrimental effect on the mosquito, which remains infected for life.[6] Aedes aegypti is particularly involved, as it prefers to lay its eggs in artificial water containers, to live in close proximity to humans, and to feed on people rather than other vertebrates

Dengue fever, an infectious tropical disease found in more than 100 countries, has no cure and no vaccine. One reason why it has been difficult to develop new drugs for dengue fever is that there are no good animal models of the disease, which only infects humans.

Dengue and Platelet count

In the new study, which appears in the Journal of Virology, the researchers set out to study one of dengue fever’s common effects — the depletion of blood platelets, which are necessary for blood clotting.

Two theories have been proposed to explain platelet depletion. One is that in some people, antibodies activated by the viral infection also attack their own platelets. The other theory is that the infection somehow interferes with platelet production, which occurs in the bone marrow.

The MIT team found two pieces of evidence to support the second theory. First, their mice lost human platelets even though they did not produce a strong antibody response to the virus. Second, the researchers found that in the bone marrow, cells that eventually become platelets, known as megakaryocytes, were also depleted.

Lab test

In 2011, the U.S. Food and Drug Administration (FDA) approved a blood test called the DENV Detect IgM Capture ELISA to diagnose people with dengue fever. The FDA notes that the test may also give a positive result when a person has a closely related virus, such West Nile disease

Cure

Dengue fever, an infectious tropical disease found in more than 100 countries, has no drug and no vaccine. One reason why it has been difficult to develop new drugs for dengue fever is that there are no good animal models of the disease, which only infects humans.

Reference

http://news.mit.edu/2013/how-dengue-fever-virus-depletes-blood-platelets-1003

http://www.aiims.edu/aiims/health%20information%20zone/AIIMS%20Public%20Lecture%20Dengue%20Fever-21-08-2014%20Final_15_10_14.pdf

http://www.medicinenet.com/dengue_fever/page4.htm

https://en.wikipedia.org