Mesothelioma and the Simian Virus 40
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Simian virus 40, or SV40, might contribute to the development of mesothelioma and some other cancers. Asbestos exposure is the leading cause of mesothelioma, but some people develop this rare cancer without it. People may be contaminated with the simian virus 40 through vaccines, resulting in an increased risk for developing mesothelioma in the setting of other risk factors, such as asbestos exposure.
What Is Simian Virus 40?
SV40 is also known as simian virus 40 and simian vacuolating virus 40. SV40 is an infectious pathogen found in both humans and monkeys. Researchers discovered it as a contaminant in polio vaccines in the 1960s.
Ultimately, they determined that 90% of children and 60% of adults who received the polio vaccine between 1955 and 1963 were given vaccines that contained SV40.[1]
What Type of Virus Is SV40?
SV40 is a polyomavirus, a group of viruses that are found in mammals and birds. Polyomaviruses are DNA-based and can cause tumors in animals. Researchers have found SV40 DNA in certain tumors in human patients, including bone and brain tumors, mesothelioma, and lymphomas.
Who Is Susceptible to SV40 Infection?
SV40 has since been found in many wild monkey populations, where it is primarily dormant and does not cause signs of infection.
However, monkeys with SV40 and suppressed immune systems can experience problems like kidney disease and tumors. SV40 has been used extensively in cancer research because it readily triggers tumors in laboratory animals.
In humans, anyone who received the polio vaccine between 1955 and 1963 could have been infected. Natural infections in people are rare, mostly occurring in those who live near or work with monkeys that carry SV40.[2]
Studies show that SV40 circulates in the human population at very low levels. There is some evidence that humans transmit it to each other through bodily fluids or contact with feces.[2]
How Did SV40 Get into Vaccines?
The inclusion of SV40 in vaccines for polio was accidental. The early forms of the polio vaccine were cultured in the kidney cells of rhesus monkeys. Researchers now know that these monkeys are primary carriers of the virus and that they often carry the virus in their kidney cells.
Does SV40 Cause Mesothelioma or Other Cancers?
A few early studies concluded SV40 did not cause cancer in humans. There was little research on the effects of SV40 between the 1960s and 1990s. However, several researchers began studying the virus and cancer in the 1990s.
These studies suggest SV40 could contribute to tumor development in humans, including those tumors that cause mesothelioma. The idea remains controversial, but evidence of a connection continues to grow.
Early Mesothelioma and SV40 Studies
In one study, a researcher injected hamsters with SV40. Each of these infected hamsters developed and died from mesothelioma.[1]
A mesothelioma surgeon joined the study. He used an extensive collection of biopsy samples from mesothelioma patients to check for the presence of SV40.
Sixty percent of the human mesothelioma samples contained the virus. Noncancerous control tissue samples from the patients did not contain the virus.[3] The work of these early researchers has since been replicated in other laboratories worldwide.[4]
Additional SV40 Studies Point to Polio Vaccines
More recent studies of SV40 and cancer show further evidence it could be a cause of mesothelioma. These studies looked for the virus in mesothelioma patients in Finland, Turkey, Italy, and the United States.
The researchers found no SV40 in the Finnish and Turkish samples. The American and Italian samples did contain SV40. Because Turkey and Finland never used polio vaccines contaminated with the SV40 virus, this helps implicate the virus as a contributing cause of mesothelioma.[1]
Critics of the SV40 Hypothesis
Although research into the connection between SV40 and mesothelioma is intriguing, the idea remains controversial. More than forty published studies have reported SV40 in various types of tumors, but other studies have failed to find the connection.
Two studies have failed to find evidence of SV40 in mesothelioma tissue samples. In one of these studies, researchers reported finding no SV40 in fifty biopsy samples.
The government has consistently cited these two papers as evidence that SV40 is not connected to mesothelioma or other types of cancer. Not only did these two studies fail to find the virus, but the authors criticized the methods used in the studies that did find SV40 in human tumors.
Public health officials might possibly deny a connection between SV40 and mesothelioma because they do not want the public to panic. When people refuse vaccinations, diseases that have been mostly eradicated can return with a vengeance.
Critics of the SV40 cancer link point out that studies that found the virus in tumors also failed to prove no laboratory contamination occurred. These researchers also failed to prove SV40 came specifically from the polio vaccine. In addition, there is no evidence that the virus found in the tumors caused the cancer. It is possible it was just a passive or benign contaminant.
The International Mesothelioma Interest Group
The International Mesothelioma Interest Group set out to determine if the virus could be consistently found in mesothelioma tissue samples. In a tightly controlled study that included four independent laboratories, researchers found that SV40 was present in most mesothelioma samples.
They also proved that the virus did not originate from laboratory contamination. Although the evidence seems strong, critics still disagree that the virus could contribute to mesothelioma.[1]
Research continues to determine the role of SV40 in mesothelioma and other cancers. Some researchers insist it is involved, while others deny that possibility.[4]
Recent Evidence of SV40 Causing Mesothelioma
The contaminated polio vaccines did not cause a significant increase in mesothelioma cases. However, the research is compelling and shows a likely connection between the virus and mesothelioma.
The most recent studies show that SV40 transforms more readily transforms some cell types to malignancy than others. Mesothelioma cells are particularly susceptible to malignancy when infected by SV40.
Researchers suggest that SV40 might not cause mesothelioma or other cancers but could lower the threshold. In other words, it makes it easier for a tumor to develop in particular cells, especially with other risk factors, like asbestos exposure.[5]
Whether we will discover the truth remains to be seen; however, the cause is no longer an important issue for many mesothelioma patients. For them, treatment advancements and options are more important. Researchers are working on that as well. Understanding how a disease like mesothelioma develops is important for prevention, diagnosis, and treatment.
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Anne Courtney has a Doctor of Nursing Practice degree and is an Advanced Oncology Certified Nurse Practitioner. She has years of oncology experience working with patients with malignant mesothelioma, as well as other types of cancer. Dr. Courtney currently works at University of Texas LIVESTRONG Cancer Institutes.