Flaviviridae

This is a family of (+) single-strand RNA viruses that have 3 important structural proteins and a host-derived lipid layer. Below is a simplified diagram on Hepatitis C virus, which belongs to the flaviviridae family.

 Generally, it is  genetic material-containing icosahedron in a lipid-containing envelope. Now, onto the members of this family.

First, let's meet the most important arbovirus (insect-borne) virus today - Dengue.

Dengue- 

It has 4 serotypes, DEN-1, DEN-2, DEN-3 AND DEN-4, based on neutralisation test. DEN-2 has the greatest antigenic and genotypic distance from the others. It is spread by the Aedes aegypti, or Aedes mosquito. 

It causes dengue fever, which has asymptomatic infections. Acute infections has the following symptoms: severe frontal headache, nausea and vomiting. Sever muscle and bone pain are also experiecnced.  

Dengue Haemorrahagic Fever or Dengue Shick Syndrome may also occur. It's symptoms are similar to that of dengue fever, HOWEVER, remission occurs, resulting in the sudden deterioriation of the patient's condition. Severe prostration, hypotension, collapse of the circulatory system, bleeding and shock follows. It can be catergorised into 4 grades. 

Now, onward to pathogenesis. Despite intensive studies conducted, pathogenesis of dengue haemorrhagic fever(DHF), is not really understood, However, there are 2 theories, both of which I will present.

(I)Virulent strain theory

Some strains are more virulent than others, with molecular studies showing variance in sequences among different strains withinserotypes, and early evidence points to DEN-2

(II)Antibody enhancement

This is the main theory, as these cells, the monocytes and marcophages are the main target for the DHF viruses. 

Wow, this was a long post, so I'll be covering on Yellow fever in the next one!! But I realised that something so simple as discarding stagnant water can prevent the breeding of these mosquitos, and eventually, the prevention of such disease. So, get rid of stagnant water, cause Prevention is better that Cure.