ADENOVIRUS SEROTYPES 4 & 7
According to a recent report published by the CDC, 49 different adenovirus serotypes have been identified. These serotypes cause a variety of different illnesses in people, such as respiratory illness, gastroenteritis, conjunctivitis, cystitis, and rash illnesses.
Acute Respiratory Disease (ARD) is most frequently caused by serotype 4 and serotype 7. During World War II, epidemics of ARD were frequent in the military. This disease was first noticed in the military and usually only affected the young military recruits. Once they had recovered from ARD, re-infection by the same serotype did not occur. New inductees into the military were particularly vulnerable to the disease because of the extreme fatigue and overcrowding that soldiers endured. In college students, a group of people of comparable age to the soldiers, epidemics of ARD did not occur. This strongly suggests that overcrowding sleeping conditions, stress, and exhaustion were important factors that contributing to disease outbreak. (Clearly, these college students were not enrolled in Dr. Siegel's Humans and Viruses course at Stanford University.)
Though the ARD respiratory symptoms are usually not severe, death can result from an accompanying case of pneumonitis. Most cases of ARD occurred during the winter. Interestingly, before the development of a vaccine, nearly 80% of new recruits were infected with ARD, and about 20%-40% needed to be hospitalized. Influenza A outbreaks could be distinguished from Adenovirus 4 and 7 outbreaks because Adenoviruses only affected the new military recruits, whereas Influenza A was less selective.
After 4 days of illness, little to no virus was detectable in the body. Consequently, the course of the disease is very rapid. Transmission of Adenovirus 4 and 7 is through the respiratory route. If the virus is aerosolized and inhaled into the lungs, disease will result. Other routes of transmission fail to produce infection.
Though serotypes 4 and 7 are almost entirely responsible for ARD, they are also sometimes responsible for other illnesses as well. Serotype 7 has been linked to acute febrile pharyngitis in infants and young children. It has also been linked to pharyngoconjunctival fever in school-aged children. Both serotypes 4 and 7 have been causally linked to ARD and pneumonia, however.
In the military, a vaccine for adenovirus serotypes 4 and 7 is used to prevent epidemics. As of now, this vaccine is not available for civilian usage, though it has already been shown to be effective in the military. The vaccine is attenuated because it exposes the body to the virus by an alternate route of transmission. The two serotypes, 4 and 7, are put in a capsule and swallowed. Consequently, the virus is not able to replicate until it reaches the intestine¾ the respiratory epithelium is avoided completely. The reason why the vaccine most likely works is that it alters the route of transmission, not because it has mutations in the genes that make serotypes 4 and 7 virulent. When the body is exposed to the virus by this route, disease does not result, though a strong antibody response is produced.