Viruses are interesting infectious organisms because they have no capacity to reproduce on their own. They infect the cells of living organisms from plants to people, hijacking the host’s cellular machinery to reproduce itself. Hundreds of viruses infect humans. Some infections are so mild they usually go unrecognized. Other viruses can rapidly cause death. You will contract many viruses throughout your lifetime--and chances are you have already contracted one or more types of common human viruses.
The U.S. Centers for Disease Control and Prevention (CDC) states more than 200 viruses can cause the common cold--and rhinoviruses lead the pack. In a review article on rhinoviruses published in the “Archives of Internal Medicine,” Dr. Stephen Greenburg noted this group of viruses causes more than 50 percent of all colds.
Rotavirus infections are the leading cause of severe diarrheal illness in children. The CDC reports that roughly 55,000 children are hospitalized with rotavirus each year in the U.S. More than 500,000 children die annually of the illness worldwide. Rotavirus symptoms include abdominal pain, vomiting and watery diarrhea, which persist for three to eight days. Adults are susceptible to rotavirus gastroenteritis, but the illness is typically much milder than it is in young children. The U.S. Advisory Committee on Immunization Practices recommends routine immunization against rotavirus for all children beginning at age 2 months.
Herpes Simplex Viruses
Herpes simplex viruses are common worldwide. Two versions of the virus, herpes simplex virus 1 and 2, cause a wide spectrum of human infections. Genital herpes, cold sores, herpes eye infections, herpes encephalitis (brain infection) and congenital herpes are common HSV infections. A distinguishing characteristic of HSV infection is the cycle of dormancy and reactivation. Once infected with HSV, the virus remains in the body. During inactive periods, HSV remains dormant in nerve cells. The viruses, however, are capable of reactivating and causing another round of symptoms if triggered.
There are more than 100 types of human papillomaviruses. They cause benign epithelial skin growths better known as warts. Plantar warts commonly occur on the soles of the feet. Common warts occur on the hands or feet. Plane warts are most common in children and usually occur on the neck, face or hands. Of greatest public health concern are sexually transmitted genital warts caused by 30 different types of HPV. The CDC reports 20 million Americans are currently infected with genital warts; 6 million new infections occur annually. A group of high-risk genital HPVs can lead to cervical cancer. Vaccines that protect against infection with some—but not all—of the high-risk HPVs are currently available.
Humans commonly contract influenza viruses type A and B, which cause seasonal flu. Influenza type A typically causes a more severe form of the illness than does type B. Only influenza type A causes pandemic influenza outbreaks. The unpredictability, capacity for pervasiveness, and potential for lethality of influenza viruses was demonstrated during the global influenza pandemic of 1918, known as the Spanish flu. In a 2006 article published in the CDC journal “Emerging Infectious Diseases,” Drs. Taubenberger and Morens point out that one-third of the worldwide population was infected during the 1918 flu pandemic, which caused an estimated 50 million to 100 million deaths.