Yellow fever

Yellow fever is an acute viral hemorrhagic disease transmitted by infected mosquitoes.

Causal agent

Yellow fever virus (family Flaviviridae and genus Flavivirus) is related to West Nile, Zika, dengue and Japanese encephalitis viruses. 

Transmission

Yellow fever virus is transmitted to humans primarily through the bite of infected Aedes or any other Haemagogus species mosquitoes. Mosquitoes acquire the virus by feeding on infected primates (human or non-human). People infected with yellow fever virus are infectious to mosquitoes (referred to as being "viremic") shortly before onset of fever and up to 5 days after onset of fever. However, the virus has been found in the blood up to 17 days after onset of illness. 

Risk groups

Risk groups include unvaccinated travelers to endemic areas, forest workers in endemic areas, and those living near forest areas or in A. aegypti infested areas who have not been vaccinated against yellow fever. The disease is highly communicable where many susceptible people and abundant vector mosquitoes coexist. Transient passive immunity in infants born to immune mothers may persist for up to 6 months. 

Symptoms

• Most people infected with yellow fever virus will either have no symptoms or mild symptoms and completely recover.
• For people who develop symptoms, the time from infection until illness is typically 3 to 6 days.
• Initial symptoms can include sudden onset of fever, chills, severe headache, back pain, general body aches, nausea, vomiting, fatigue (feeling tired), weakness. o Most people who develop symptoms improve within one week. o For some people who recover, weakness and fatigue (feeling tired) might last several months.
• A few people will develop a more severe form of the disease.  For 1 out of 7 people who have the initial symptoms, there will be a brief remission that may last only a few hours or for a day, followed by a more severe form of the disease. Severe symptoms include high fever, yellow skin or eyes (jaundice), bleeding (from the mouth, nose, eyes or stomach), shock, and organ failure. 

Prevalance

Yellow fever is endemic in tropical areas of Africa and Latin America. Travelers going to these places are at risk for infection with the virus. There is no evidence that yellow fever has ever been present in Asia, but disease is considered as a disease of public health emergency of international concern and even a single case would be termed as an outbreak.

In India, the conditions for transmission of yellow fever are very conducive due to the presence of mosquito vectors in abundance and susceptible population, therefore there is a greater need for vigilance and the focus for prevention of disease spread is at the Point of Entries (POEs).  

Treatment

No specific antiviral therapies available; treatment is supportive. Good and early supportive treatment in hospitals improves survival rates. 

Prevention

• Yellow fever is prevented by an extremely effective vaccine, which is safe and affordable. A single dose of yellow fever vaccine is enough to grant sustained immunity and life-long protection against yellow fever disease. A booster dose of the vaccine is not needed. The vaccine provides effective immunity within 10 days for 80-100% of people vaccinated.
• All passengers coming to India or passengers going from India to countries endemic for Yellow Fever should have a valid International Vaccination Card for Yellow Fever from a designated yellow fever vaccination center. 

Laboratories for testing YF

1. National Centre for Disease Control, New Delhi
2. ICMR-National Institute of Virology, Pune
3. ICMR-National Institute of Cholera and Enteric Diseases (NICED), Kolkata, West Bengal
4. All India Institute of Medical Sciences (AIIMS), Bhopal, MP
5. Sawai Man Singh (SMS) Medical College, Jaipur, Rajasthan
6. King George’s Medical University (KGMU), Lucknow, UP
7. King Institute of Preventive Medicine & Research (KIPMR), Chennai, Tamil Nadu
8. Jawaharlal Institute of Postgraduate Medical Education & Research (JIPMER), Puducherry
9. Regional Medical Research Centre (RMRC), Dibrugarh, Assam
10. Sher-i-Kashmir Institute of Medical Sciences (SKIMS), Srinagar, Jammu & Kashmir
11. BJ Medical College, Ahmedabad, Gujarat
12. Postgraduate Institute of Medical Education & Research (PGIMER), Chandigarh
13. ICMR-National Institute of Virology, Bangalore Unit
14. ICMR- National Institute of Virology Kerala Unit 

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