Viruses have been identified as the cause of at least 50 recognized diseases. Some viruses have been implicated as the cause of cancerous tumors in animals and a few as contributing to cancer in humans. It is possible that there are as yet unidentified hazards with exposure to viruses.

Individuals may become infected with viruses in the laboratory, by inhalation, ingestion, inoculation, or other direct contact. These individuals may then develop symptoms or may remain nonsymptomatic carriers. In either case, they may transmit the viral infection to others by direct contact or by indirectly shedding viruses onto inanimate objects (fomites).  Infants and young children are particularly susceptible to viral infections. Some viral infections are more serious when they occur in pregnant women. Viruses may cross the placenta to the fetus and may result in miscarriage, fetal death, fetal infection, or developmental abnormalities.

The viruses currently in use in research at Princeton University are:

1. ADENOVIRUSES  -  There are 49 distinct types of adenoviruses, which most commonly cause upper respiratory infections.  However, adenoviruses may also cause illnesses ranging from gastroenteritis and conjunctivitis to urinary tract infections and exanthems.  Symptoms associated with adenovirus infection in the respiratory tract may include runny nose, sore throat, and cough.  Adenovirus infection may also cause pneumonia, croup, and bronchitis.  People with immune system compromise may be at especially high risk of severe complications of infection with adenovirus.


Adenoviruses are transmitted by direct contact with bodily fluids, fecal-oral routes, and occasionally via water (in poorly chlorinated swimming areas).  Certain types of adenoviruses are associated with specific diseases: serotypes 8, 19, and 37 are associated with conjunctivitis, acute respiratory disease is associated with serotypes 4 and 7, and gastroenteritis is most commonly associated with serotypes 40 and 41.  However, route of transmission can affect clinical manifestations (for example, inhalation infection with serotype 7 can cause severe lower respiratory tract disease, whereas oral transmission of the same serotype causes mild disease).

There is no virus-specific treatment for infection with adenovirus and since most infections are not life threatening, therapy is directed towards alleviating symptoms.  In more complicated infections, treatment is supportive.
Source:  CDC website.
 
2. HERPES SIMPLEX VIRUSES  -  Herpes simplex viruses (HSV-1 and HSV-2, Herpesvirus hominis) are double stranded DNA viruses which cause a spectrum of diseases ranging from skin and mucous membrane infections to central nervous system and systemic infections.    Herpes simplex viruses are unusual because they can cause an initial infection and then exist in a dormant state in the affected person’s neurons.  Therefore, an infected person can develop reactivation disease at a later time.


HSV-1 is usually contracted early in life, with seroprevalence rates of approximately 90% by the fifth decade.  HSV-2 usually infects people later in life, with recent seroprevalence rates of approximately 22% among adults in the United States.  It used to be thought that HSV-1 caused infections “above the belt” and HSV-2 “below the belt”, but it is now known that HSV-1 and 2 can infect almost any site as long as there is adequate contact with a person who is actively shedding virus.  In fact, a person may shed virus without having clinically apparent lesions and this is thought to be contributing to an enormous rise in seroprevalence rates for HSV-2 in the United States.

Infections can occur almost anywhere, with the most common sites being the oral-labial and genital areas.  HSV may also cause encephalitis, a rare but serious infection of the central nervous system.  Another dangerous complication of HSV infection is HSV keratitis, an infection of the eye.  Untreated Herpes keratitis is a major cause of blindness.  Neonatal HSV infection can cause many serious complications and has a 25% mortality rate, even when treated.  HSV infections are more serious and recur more often in immunosuppressed individuals.

Prevention of HSV infection in the lab includes using universal precautions when handling infectious material.  Once a person is infected, treatment consists of antiviral medication used to shorten outbreaks or used prophylactically to prevent recurrences.  Topical penciclovir has been shown to be effective with oral-labial herpes infections, while oral acyclovir and its sister drugs valacyclovir and famciclovir are effective in genital herpes.  With neonatal infection, prevention is geared towards recognition of affected mothers and delivery by caesarian section.  Work on a vaccine is underway, but as yet does not exist for use in the general public.

Source:  Harrison’s Textbook of Internal Medicine, 15th edition, pages 1100-1106.
 
3. HUMAN CYTOMEGALOVIRUS  -  Cytomegalovirus is a member of the herpesvirus family, which includes Herpes simplex virus, Varicella-zoster virus, and Epstein-Barr virus.  It also has the ability to infect its host and then become dormant.  CMV causes diseases ranging from a mono-like illness and hepatitis to severe congenital infection which can result in malformations.


Transmission of CMV involves repeated or prolonged exposure to infectious material.  It is estimated that 50-85% of adults in the United States have been infected by age 40, and most people do not realize that they have contracted CMV.  CMV infection usually causes a mono-like illness and therefore is not usually life threatening.  However, it can be a serious infection in the immunocompromised or pregnant host.

CMV infection is the most common viral infection affecting transplant patients, and can cause problems such as fever, hepatitis, pneumonitis, and may play a part in organ rejection and death.  CMV is also responsible for serious infections in persons infected with HIV, including retinitis and pneumonitis.

In the pregnant patient, CMV can cause congenital infections.  Approximately 1-3% of women in the United States have primary CMV infection while pregnant and the most serious congenital infections occur almost exclusively in mothers who develop a primary infection during pregnancy.  Approximately one third of fetuses whose mothers have a primary infection will become infected with CMV.  Some of the complications of congenital infection in the fetus include microcephaly, intrauterine growth retardation, and premature delivery.  This results in a 20-30% mortality rate for the infant, and those who survive are often mentally and physically compromised.

Treatment of CMV infection can involve antiviral drugs such as ganciclovir, foscarnet, and cidofovir.  There are vaccines in the research stages, but they are not yet available to the public.  Prevention of CMV remains an important issue for pregnant women who are known to be seronegative and have significant risk for exposure to the virus, and for those who are known to be immunocompromised.

Sources:  Harrison’s Textbook of Internal Medicine, 15th edition, pages 1111-1115, and CDC website.

5. NON-HUMAN RETROVIRUSES  -  Many retroviruses tend to be species-specific.  There are a number of non-human retroviruses that cause tumors in animals such as chickens, mice, cats, and primates.  Those working with non-human retroviruses are not required to be in the Live Virus Worker Program.