Variola Virus Presented by Megan Eline Orthopox Characteristics

Variola Virus Presented by Megan Eline

Orthopox Characteristics n Belongs to Orthopoxidae Family n Very large, brick-shaped virus. n 300 X 200 nm in size. n ds. DNA genome (200 kbp). n Virus particle is enveloped and contains filamentous nucleocapsid

What is Smallpox? n A serious, contagious, often fatal disease caused by the variola virus. n 2 Clinical forms: – Variola major – Variola minor Pustules

Early History of Smallpox n Origin is uncertain, but believed to have originated in Africa, which then spread to India and China. n Smallpox reached Europe between the 5 th and 7 th centuries n Epidemics occurred in the North American colonies in the 17 th and 18 th centuries

Epidemiology n n n The first recorded smallpox epidemic was in 1350 BC during the Egyptian-Hittite war. In the London epidemic of 1857 -1859, there were 14, 244 deaths; in the 1863 -1865 outbreak - 20, 059 deaths. Japan-1892 their records showed 165, 774 cases with 29, 979 deaths. In the Philippines between 1917 and 1919, 162, 503 reported cases and 71, 453 deaths. In the 20 th century alone, an estimated 300 million people died from the disease.

Smallpox gets defeated n Last known case in the United States was in 1949. n Last known naturally occurring case in the world was in Somalia in 1977. n Except for laboratory stockpiles, the virus has been eliminated.

Dr. Edward Jenner n Observed that farmers who caught cowpox never caught smallpox. n 1798 he introduced cowpox vaccination for smallpox. n James Phipps was the first person to receive the vaccine and he did not become infected.

Symptoms n Fever (101°-104°F) n Occasional vomiting n Malaise n Rashes n Head and body aches n Pustules

Transmission Humans are the only natural hosts. n To survive, the virus must pass from person to person. n Inhaled droplets of air or aerosols enters through respiratory mucosal route. n Direct or prolonged face-to-face contact required with infected person. n Bodily fluids or contaminated objects. n

Replication Process (Lytic Cycle) n n n Binding to cell receptors and penetration of host cell. Uncoating of protein coat. Gene expression and transcription. Genome replication (occurs in the cytoplasm). Assembly and release of new virions. Replication occurs in ~12 hours.

Variola Virus Replication

Infection Process n n Incubation Period (7 -17 days) – No symptoms occurring. – Virus replicates in lymph nodes. – Not contagious. Prodrome Period (2 -4 days) – Initial symptoms occurring. – Virus replicates in spleen, bone marrow, & lymph nodes. – Sometimes contagious.

n Early Rash (4 days) – Small red spots on tongue and in mouth. – Spots develop into sores. – Most contagious phase!!! – Rash appears on skin & spreads over body within 24 hours. – Fever develops.

n Third day - raised bumps appear. n Fourth day bumps fill up with a thick, opaque fluid. – Fever increases and remains high until scabs form. n Pustular Rash (5 days) – Pustules form. – Contagious.

n Pustules and Scabs (~5 days) – – n By the end of second week after rash appears, most sores are scabbed over. – Contagious. Resolving Scabs (~6 days) – – n Pustules form a crust and scab Scabs fall off and leave scars. Contagious. Scabs Resolved – Once the last scab has fallen off, the person is no longer contagious.

Diagnostic Tests n Routine viral cultures. n Variola PCR targets the hemagglutin gene. n Electron Microscopy.

Prognosis n Variola major fatality rate is 30%. – Hemorrhagic & flat smallpox have >90% fatality rate. n Variola minor fatality rate is <1%.

Preventative Measures n Smallpox vaccine provides a high level of protection against the disease for about five years. Without the vaccine, it is nearly impossible to prevent infection. n Contains live vaccina virus. n Does not contain smallpox and does not cause smallpox.

More Preventative Measures • Good hand hygiene. • Isolation of suspected smallpox patients. • Keep sites covered with gauze.

Smallpox as a Biological Weapon n Smallpox was used as a biological weapon during the French-Indian wars in the United States (1754 -1767), when British soldiers gave the Indians blankets that had been used by smallpox patients. n Japan considered the use of smallpox as a biological weapon in World War II. n Smallpox is currently contained in two high security labs (United States and Russia). n Rated among the most dangerous of all potential biological weapons.

Shared modes of protection against poxvirus infection by attenuated and conventional smallpox vaccine viruses n n Trying to develop a safer vaccine due to a more immunocompromised population of individuals (ie. AIDS, chemotherapy for cancer, organ transplant). Used modified vaccinia Ankara and NYVAC replication -deficient vaccinia viruses If vaccine is present at time of virulent strain, then the antibody is sufficient to protect the host and T cells are not necessary. If no prior immunity, then T cells and antibodies must both respond. T cells are more efficient & clear infection better than antibodies.

QUIZ!!!! n When is smallpox the most contagious? Name 3 symtoms of smallpox. n T or F Humans are not the only natural hosts of the variola virus. n When was the last known case of smallpox in the United States? n

Resources n n n www. cdc. gov. The New Mexico Epidemiology Report, Volume 2003, Number 4. Ward, Brian. , Epidemic. New York, Dorling Kindersley Publishing, Inc. , 2000 Prescott, Lansing M. , John P. Harley, Donald A. Klein, Microbiology, New York, Mc. Graw-Hill 2002 http: //dermatology. about. com/cs/smallpox/a/sma llpoxhx. htm www. aafp. org/afp/ 20030901/889. html

Resources Continued n n n http: //www. whale. to/v/smallpox 1. html http: //www. cnn. com/HEALTH/library/DS/00424. html cidrap. umn. edu/cidrap/content/bt/smallpox/bi ofacts/smllpx-summary. html www. pnas. org. http: //dermatology. about. com/cs/smallpox/a/sma llpoxhx. htm www. aafp. org/afp/ 20030901/889. html