Slow virus

A slow virus is a virus, or a viruslike agent, etiologically associated with a slow virus disease. A slow virus disease is a disease that, after an extended period of latency, follows a slow, progressive course spanning months to years, frequently involves the central nervous system, and in most cases progresses to death. Examples of slow virus diseases include HIV/AIDS, caused by the HIV virus,^[1] subacute sclerosing panencephalitis, the rare result of a measles virus infection,^[2] and Paget's disease of bone (osteitis deformans), which may be associated with paramyxoviruses, especially the measles virus and the human respiratory syncytial virus.^[3]

Characteristics

Every infectious agent is different, but in general, slow viruses:^[4]

• Cause an asymptomatic primary infection
• Have a long incubation period ranging from months to years
• Follow a slow but relentless progressive course leading to death
• Tend to have a genetic predisposition
• Often re-emerge from latency if the host becomes immuno-compromised

Additionally, the immune system seems to plays a limited role, or no role, in protection from many of these slow viruses. This may be due to the slow replication rates some of these agents exhibit,^[5] preexisting immunosuppression (as in the cases of JC virus and BK virus),^[6] or, in the case of prions, the identity of the agent involved.^[7]

Scope

Slow viruses cause a variety of diseases, including cancer.

Examples of viral agents

Virus	Virus family	Disease	Typical latency	Transmitted by
JC virus (Human polyomavirus 2)	Polyomavirus	Progressive multifocal leukoencephalopathy	Years to Life§	Unknown; possibly contaminated water[6]
BK virus	Polyomavirus	BK nephropathy, bladder cancer[8]	Years to life§	Unknown; possibly respiratory spread/urine; possibly contaminated water[6]
Measles virus	Paramyxovirus	Subacute sclerosing panencephalitis	1–10 years	Respiratory droplets[9]
Rubella virus	Togaviridae	Progressive rubella panencephalitis	10–20 years	Respiratory droplets[10]
Rabies virus	Rhabdoviridae	Rabies	3–12 weeks	Bite of an infected animal[11]
Human papillomavirus infection	Papillomaviridae	Cancers of the cervix, oropharynx, vulva, anal, penis, vagina and rectum.	Years	Sexual activity[12]

^§JC virus & BK virus only cause disease in immunocompromised patients

See also

• Clinical latency
• Virus latency