Viral Hemorrhagic fever Flashcards
An infectious disease is a result of?
forces within a dynamic system that consists of the agent of infection, the host, and the environment. This is the classical epidemiological triad.
What is Viral Haemorrhagic fever?
Viral haemorrhagic fevers (VHFs) are a group of diseases caused by several distinct virus families.
The term ‘viral haemorrhagic fever’ is a term used to denote the clinical presentation of a multisystem syndrome where the vascular system is damaged resulting in severe, uncontrolled haemorrhage
VHF as defined by the WHO?
A general term for a severe illness, sometimes associated with bleeding, that may be caused by a number of viruses
VHF is caused by 4 distinct families, name them
Arenaviridae, Bunyaviridae, Filoviridae, Flaviviridae.
Arboviruses
- Flaviviruses
- Bunya viruses
- Reoviruses
Not arboviruses
- Bat viruses
2. Rodent viruses
Mosquito-borne [flaviviruses]
Yellow fever
Dengue fever
Mosquito-borne [Bunyaviruses]
Rift valley fever
Filoviruses [Bat viruses]
Ebola
Marburg
Characteristics of Virus
These viruses all share some similar features:
> Enveloped single-stranded RNA viruses
Zoonoses and have an animal reservoir of infection*
Geographically restricted to the location of the host.
No cure or proven drug treatment for most of these infections.
- The viruses associated with VHF are zoonotic.
- Their natural host is the animal reservoir or arthropod vector.
- They are, therefore, completely dependent on their hosts for replication and overall survival.
- Man is just an incidental host
- Infectious during viremia phase
- Low infectivity dose [get sick with just a small dose of the virus]
Biological Weapon
- Haemorrhagic fever viruses have been used as biological weapons in the past by world powers and by cult groups.
- A bioweapon, based on the potential for person-to-person transmission, their potential to cause widespread illness and death, potential for major public health impact and the necessity for special action for public health preparedness.
Epidemiology of Viral Haemorrhagic fever
-Zoonoses- Rodents and arthropod vectors are main reservoirs
- Infections of humans
>Bite of infected arthropod
>Aerosol from infected rodent excreta
>Direct contact with formites or infected rodent carcass
-Human to human infection
Direct contact with infected blood or body fluids
General pathogenesis of the viruses
Target organ- Vascular bed
Cytokines - Hypotension and tension
Affect platelet function and numbers.
The virus gets into the host and replicates and gets into macrophages and dendrites. It then stimulates the IMMUNE RESPONSE which leads to increased vascular permeability and clots every part of body = plasma leak out and bleeding organ impairment, onset is very sudden.
Case fatality rate
- Case-fatality rates of patients with VHF vary from less than 10% (eg, in dengue HF) to as high as 90%, as has been reported in some filovirus outbreaks.
- The case-fatality rate for the 2014-2016 West Africa Ebola outbreak was ~40%.
Dengue fever cause
- Dengue is a vector-borne viral infection and a globally important public health problem.
- The dengue viruses (serotypes 1, 2, 3, and 4) are enveloped,single-stranded RNA virusesof theFlaviviridaefamily.
- Transmission from human to human is predominantly by the mosquitoAedes aegypti [a mosquito], which bites in the daytime, is adapted to human habitats, and has a preference for human blood meals.
- More than 1 billion people are at risk of dengue infection in over 100 countries
Dengue fever recovery
Recovery from infection is believed to provide lifelong immunity against that serotype. However, cross-immunity to the other serotypes after recovery is only partial, and temporary. Subsequent infections (secondary infection) by other serotypes increase the risk of developing severe dengue DENV is frequently transported from one place to another by infected travellers; when susceptible vectors are present in these new areas, there is the potential for local transmission to be established.
Epidemiology of Dengue fever
Modelling estimate indicates 390 million dengue virus infections per year (95% credible interval 284–528 million),
96 million (67–136 million) manifest clinically (with any severity of disease).
Another study on the prevalence of dengue estimates that 3.9 billion people are at risk of infection with dengue viruses.
70% of the actual burden is in Asia
The number of dengue cases reported to WHO increased over 8 fold over the last two decades, from 505,430 cases in 2000, to over 2.4 million in 2010, and 5.2 million in 2019.
Reported deaths between the year2000 and 2015 increased from 960 to 4032.
Key facts on dengue fever.
Dengue is a mosquito-borne viral infection, found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.
The virus responsible for causing dengue is called dengue virus (DENV). There are four DENV serotypes, meaning that it is possible to be infected four times.
While many DENV infections produce only mild illness, DENV can cause an acute flu-like illness. Occasionally this develops into a potentially lethal complication, called severe dengue.
Severe dengue is a leading cause of serious illness and death in some Asian and Latin American countries. It requires management by medical professionals.
- There is no specific treatment for dengue/severe dengue. Early detection of disease progression associated with severe dengue, and access to proper medical care lowers fatality rates of severe dengue to below 1%.
- The global incidence of dengue has grown dramatically in recent decades. About half of the world’s population is now at risk. There are an estimated 100-400 million infections each year.
- Dengue prevention and control depends on effective vector control measures. Sustained community involvement can improve vector control efforts substantially.
