There are eight known human herpes viruses, and they are the most widely known latent viruses in humans. These viruses may be asymptomatic upon first exposure or cause a variety of primary diseases ranging from a sore throat to chickenpox. As the primary infection begins to subside, the viruses become latent in a variety of body tissues. Then during periods of decreased immunity, these viruses can reactivate, proliferate, and cause disease. Three of the eight human herpes viruses were routinely monitored in this study: 1) Epstein-Barr virus (EBV), 2) Cytomegalovirus (CMV), and 3) Varicella zoster (VZV). The primary technology used to detect and measure the extent of viral reactivation was the polymerase chain reaction (PCR). This molecular technology is sensitive, specific, and rapid. Viral plaque formation in tissue culture is the traditional method, but it is slow and some of the herpes viruses are difficult to culture. Culturing for viruses was used late in the study to demonstrate viable viruses. A detailed description of each virus studied is given below.
Epstein-Barr virus (EBV): EBV becomes latent in B-cells and perhaps some other tissues. When it reactivates, it can cause infectious mononucleosis in young adults. In severe immuno-suppressed individuals, EBV can promote tumor formation.
Cytomegalovirus (CMV): CMV is another herpes virus and it is shed in urine after reactivation. In addition to causing very serious congenital diseases in fetuses and newborns, it can lead to an infectious mononucleosis-type of disease in adults. This virus is found in the tissues of epithelial origin (i.e., kidney, liver, salivary glands, gut epithelium) and fibroblasts.
Varicella zoster (VZV): VZV is the etiological agent of chickenpox (primary) and shingles. VZV becomes latent in human ganglia after primary infection. VZV reactivation occurs most frequently in elderly individuals, organ transplant recipients, and patients with cancer and AIDS, correlating with a specific decline in cell-mediated and humoral immunity to the virus. VZV can reactivate following the stress of surgery and also in response to various non-surgical stressors.
Cytomegalovirus (CMV): The reactivation of cytomegalovirus (CMV) in 71 astronauts was investigated, using polymerase chain reaction. Blood and saliva samples were collected from astronauts before, during (saliva only), and after 10 space shuttle missions of five to 14 days duration.
Varicella zoster (VZV): DNA was extracted from 312 saliva samples of eight astronauts before, during, and after space flight for VZV DNA by PCR: 112 samples were obtained 234 - 265 days before flight, 84 samples on days two through 13 of space flight, and 116 samples on days one through 15 after flight. Plasma antibody titers were collected from astronauts pre- and postflight.
Epstein-Barr virus (EBV): At one time point or another, EBV was detected in saliva from each of the astronauts. Of 1398 saliva specimens from 32 astronauts, PCR analysis showed that 314 (23%) were positive for EBV DNA. Examination by flight phase showed that 29% of the saliva specimens collected from 28 astronauts before flight was positive for EBV DNA, as were 16% of those collected from 25 astronauts during flight and 16% of those collected after flight from 23 astronauts.
A significantly greater shedding frequency was found in urine samples from astronauts before space flight (10.6%) than in urine from the healthy control subject group (1.2%). The investigators found that approximately 28% of astronauts shed CMV in urine before and after space flight. Although limited by few astronaut subjects, in-flight shedding of CMV occurred in two of four astronauts.
Varicella zoster (VZV):
Before space flight, only one of the 112 saliva samples from a single astronaut was positive for VZV DNA. In contrast, during and after space flight, 61 of 200 (30%) saliva samples were positive in all eight astronauts. No VZV DNA was detected in any of 88 saliva samples from 10 healthy control subjects. These results indicate that VZV can reactivate sub-clinically in healthy individuals after non-surgical stress.
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