Dengue
P.K.Ghatak, MD.
Dengue Fever.
Dengue fever is a viral illness transmitted by mosquito bite. The virus belongs to Flaviviridi, genus Flavivirus. The Dengue virus is spherical in shape, the center of the virus is made up of viral genome and C-protein. The virus acquire a lipid envelope form its victim. The virus was identified in 1943, by Ren Kimra and Susumu Hotts from the blood samples collected during Dengue epidemic in Nagasaki, Japan.
The virus is a single-stranded positive-sense RNA virus and has 10,700 base pairs. Dengue virus mutates often in endemics and are known as DENV -1, DENV -2, DENV-3 and DENV-4. At a given time all 4 variants may be circulating in a given location.
Where Dengue is most prevent:
Febrile illness transmitted by mosquito is recorded since 1600, and were called Dengue but no serological tests were known at that time. Today, it appears that the so called Dengue is actually a collection of vector borne viral illnesses and one of them is dengue.
Dengue presently is endemic in India, and other South Indian Nations, South China, Taiwan, Pacific Islands, Caribbean, Mexico, Africa, and South and Central America. Dengue virus infects 390 million people and causes 25,000 deaths each year.
How Dengue spreads:
Two closely related mosquito species – Ades aegypti and Aedes albopictus acquire the virus by biting Dengue patients and then spread the virus to new victims. Other uncommon sources are - the pregnant mother can transmit dengue to her unborn child, infected organ transplantation and blood transfusions. The Dengue virus does not spread person to person.
What other virus illnesses are spread by Ades mosquito:
Zika virus.
Yellow fever.
West Nile fever
Chikungunya.
Previous endemics:
Many epidemics and endemics can be traced by looking into the CDC reports but confirmed endemics are as flows-
In 2023, major urban centers of India have seen wide spread dengue fever following monsoon floods.
In 2014, Brownsville Texas and Key West, Florida, and Hawaii have experience Dengue fever.
CDC reports 2,000 cases of dengue in USA and its territories in 2022..
In 1942, Nagasaki, Japan.
During 2014 to 2016 Singapore recorded 33,000 cases of dengue. A biological method was used to control the endemic and the incidence dropped to 1/3 in 2017 by releasing male Ades aegypti mosquito infected with bacteria Wolbachia. This bacteria made male mosquito sterile and as a result the mosquito population
dropped and so the incidence of dengue.
Clinical feature:
Incubation period:
3 to 10 days, from the time of the mosquito bites to the onset of fever.
Symptoms:
Abrupt on set of fever, headaches, retro orbital pain, body pain, bone pain, petechia, hematuria, hemorrhage in gastrointestinal tract and brain, prostration and some incidence of deaths.
Clinical types:
Minor fever and bone pain. Most of the patients belong to this group. Fever lasts 2 to 7 days and the fever may be biphasic. In minority of patients the symptoms are - high temperature to 104F, severe headaches, retro-orbital pain, muscular and bone pain, ecchymosis, bleeding from gums, epistaxis, hematuria, petechiae and abdominal pain.
Weakness, prostration and severe bone pain and severe hemorrhagic episodes called Dengue Hemorrhagic Fever.
Dengue shock syndrome, consists of hypotension, shock and bleeding.
Special aspect of decreased Platelet count:
Low platelet count, usually around 150,000/mL is seen in most patients and develop on 3rd and 4th day. On about 7 to 10 days the platelet numbers returns to normal. In 10 to 20 % cases the platelet number falls below 50,000 and may reach a low 20,000/mL. Only about 5% of patients require platelet transfusions. One unit of platelet requires 4 units of blood.
What causes low Platelets:
Multiple processes of low platelet count are identified.
Dengue virus infects various cell types including immune cells - monocytes, macrophages, dendritic cells, and Langerhans cells. Immune cells fail to swallow the virus, generate antibodies, fail to generate killer cells and limit spread of virus spread and fails to activate anti- inflammatory processes.
Depression of megakaryocytes in the bone marrow.
Destruction of platelets associated with activation of complement factor C3, and C5 binding to platelets. The DENV -2 alters platelets and activates macrophages to phagocytose platelets.
Dengue antigen when attached to platelet IgM and IgG, becomes antigenic and starts producing antibodies that causes destruction of platelets.
Diagnostic tests:
Blood test detects Dengue NS1 antigen and also IgM and IgG antibodies. Test kits are commercially available and marketed by SD Bioline Dengue Duo test. NS1 antigen can be detected early in the stage of the illness. This test is moderately high sensitivity and very high specific. After 10 days following infection, the serology becomes positive. IgG antibody remains positive 10 months following infection.
Treatment:
More mild to moderate cases proper hydration are maintained. For fever and pain in bones and muscles Acetaminophen is used. Aspirin, NSAID (non steroidal anti inflammatory drugs) are contraindicated because those drugs can aggravate bleeding.
Those who develop low platelet count require close monitoring platelet count and boost platelets by platelet transfusions which may have to be repeated.
“ The Janssen Pharmaceutical Companies of Johnson & Johnson (Janssen) announced, on October 2023, promising data from a Phase 2a human challenge study evaluating JNJ-1802, a first-in-class oral antiviral in development for the prevention of dengue. The data showed that the compound induced antiviral activity against dengue (DENV-3) in humans, compared to placebo, and is safe and well-tolerated. The data were announced at the American Society of Tropical Medicine & Hygiene Annual Meeting in Chicago, Illinois.”
Other measures:
To reduce infection carried by mosquito to others, the febrile patients should avoid mosquito bites. Use of these limits mosquito bites – mosquito repellents, wear long-sleep shirts and long pants and socks. Switch on the air conditioning unit. Covers windows and doors with mosquito nets.
In India Papaya fruit and extract of Papaya leaves or leaves boiled in water prove to be a reliable platelet booster. In some other Asian countries Pumpkin found to spike platelets just like papaya.
Vaccine:
Dengvaxia is the name of a vaccine approved by FDA for teenagers 9 to 16 years old to prevent recurrence of dengue infection. Serological evidence must be present before vaccine is administered otherwise dengue, if contacted, would be much worse No vaccine for adults are successful so far.
Why dengue vaccines is difficult to make:
The dengue virus stops the immune reactions and inactivates and destroy immune cells that produce antibodies. In endemic area more than one variety of dengue virus is active and dengue virus sub type 1 to 4, each one has different antigen. Even a successful vaccine against one sub type will not protect every person
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