Variola
Backgroud
Smallpox, a devastating infectious disease dreaded throughout much of recorded history, is caused by the variola virus, a member of the Poxviridae family. In the 20th century alone, smallpox deaths worldwide numbered in the millions. Smallpox disease was a feared scourge in multiple historical civilizations and was responsible for epidemics throughout human history. Notably, smallpox was the first disease for which successful prophylaxis was developed. The World Health Organization (WHO) implemented the Smallpox Eradication Program (SEP) from 1966 to 1980, which culminated in the eradication of the disease.
Structure
The variola virus, a member of the genus Orthopoxvirus, is a large, double-stranded DNA virus with a length of about 186 kb. The variola virus is a large brick-shaped particle that measures about 300 by 250 by 200 nm. The virion contains an envelope, a surface membrane, a concave core, and two lateral bodies. The genome encodes approximately 200 proteins, and over 80 of them are located in the terminal regions. And in addition, the genome comprises an extended central conserved region (approximately 102 kbp), which primarily houses the vital genes responsible for various biological process. But only several variola proteins have been characterized up to now.
Fig.1 Variola genome architecture. (Esposito, 2006)
Pathogenesis
Variola virus infection is initiated when the virus comes into contact with the oropharyngeal or respiratory mucosa of a susceptible person. The virus then multiplies in regional lymph nodes. An asymptomatic viremia develops 3 or 4 days after infection, which is followed by further virus replication, probably in the bone marrow, spleen, and lymphatics. A second viremia begins about 8-10 days after infection and is followed by the first symptoms of illness (prodromal stage), fever, and toxemia. The virus localizes in small blood vessels of the dermis and the oral and pharyngeal mucosa. In the skin, this results in the characteristic maculopapular rash, which evolves into vesicles, then pustules.
Epidemiology
The disease is highly contagious. Animals and insects don’t spread the disease. The incubation period for smallpox is 7 to 17 days. People could get it:
- By breathing in the virus during close, face-to-face contact with an infected person. It usually spreads through drops of saliva when the person coughs, sneezes, or speaks.
- By handling the clothes or sheets of an infected person or coming into contact with their body fluids.
Symptom
Early symptoms of smallpox are similar to the flu, progressing to a rash a few days later that then turns into deep sores that fill with fluid. These blisters ooze, crust, and scab over, eventually falling off and leaving scars. Other possible symptoms include:
- High fever
- Head and body aches
- Fatigue
- Sometimes vomiting
- Diarrhea
- Malaise
- Excessive bleeding
Prevention
Medical treatment for smallpox eases its symptoms because there is no known specific treatment for smallpox. The vaccination against smallpox contains the cowpox (vaccinia) virus, not the smallpox virus. Even among the general population immunized in the 1960s, hundreds of complications and several deaths were recorded as a result of vaccination, representing a safety record that would be unacceptable by today’s standards. Many immunologists, therefore, believe that a new, safer smallpox vaccine should be developed.
Scientists from Creative Biolabs are confident in providing our customers with the most reliable and cost-effective ViroAntibody to facilitate their valuable viral disease research and project development. For further information and to discuss your project needs, please feel free to contact us.
Reference
- Esposito, J.J.; et al. Genome sequence diversity and clues to the evolution of variola (smallpox) virus. Science. 2006, 313(5788): 807-812.
All products and services are intended for Research Use Only, and NOT to be used in diagnostic or therapeutic procedures.