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Five Viruses that Cause Cancer
What you need to know about these viruses and how to reduce your
risk
By Rachael
Bieschke
Five viruses have
been added to the U.S. Department of Health and Human Services 14th Report on
Carcinogens, released in November 2016.
The report
identifies environmental factors, including infectious agents, known (or
reasonably anticipated) to cause cancer.
It’s estimated
that 12 percent of human cancers worldwide are caused by viruses, which are
made up of genes (DNA or RNA) surrounded by a protein coating.
If the viral DNA
or RNA hijacks a healthy cell’s genes, it may contribute to the cell becoming
cancerous.
All five of the
newly added viruses are classified as “known to be human carcinogens.”
Together they’re
linked to more than 20 different types of cancer and include:
1. Human immunodeficiency virus type 1 (HIV-1):
This virus does not cause cancer directly but rather encourages cancer to
develop by suppressing the immune system.
HIV-1
is a sexually transmitted virus that may also be spread through sharing of
infected drug needles as well as passed from mother to child during pregnancy
or breastfeeding.
HIV-1 is linked to an increased risk of
non-Hodgkin and Hodgkin lymphomas, anogenital cancers, Kaposi sarcoma, liver
cancer, non-melanoma skin cancer, eye cancer and possibly oral cancers and lung
cancer.
As
noted by Mashiul Chowdhury, MD, chief, Division of Infectious Diseases, and
director of Infection Control and Antibiotic Stewardship Program at Cancer
Treatment Centers of America® at Eastern Regional Medical Center in
Philadelphia, Pennsylvania:
“Molecular techniques and research are
helping us to understand the link between some viruses and environmental
factors involved in developing cancer.
“Human viral oncogenesis is a complex
mechanism and fortunately, very small number of infected patients develop cancer
after initial infection.
“It is a multistep process and involves
additional host, environmental and genetic cofactors in this oncogenesis and it
sometimes take decades before full development of cancer.
“Although we do not know the mechanism
of viruses causing these cancers precisely, knowing these links may better
prepare us to prevent some of these cancers.
“For example, prevention of
transmission of HIV reduces risk of developing many cancers significantly.”
2. Human T-cell lymphotropic virus type 1 (HTLV-1):
Spread through contact with contaminated cells or biological tissues, such as
by sharing of infected needles, breastfeeding or sexual activity, HTLV-1 is
known to cause a rare form of cancer called adult T-cell leukemia-lymphoma.
According
to Dr. Chowdhury: “HTLV-1 virus is responsible for certain types of blood
cancer but not every person exposed to HTLV-1 virus will get cancer. For
example, up to 10% of Japanese people are exposed to HTLV-1 virus.
“The virus is most frequently
transmitted by mother to child by breastfeeding; however, it can also be
transmitted between people via sexual activity and blood.”
3. Epstein-Barr virus (EBV):
EBV is a herpes virus transmitted via saliva.
This
common virus infects more than 90 percent of people worldwide at some point
during their lives, most often leading to few or no symptoms (although in some
cases it causes mononucleosis, or mono).
Rarely,
EBV may cause certain types of stomach cancer, four types of lymphoma and
nasopharyngeal cancer.
4. Kaposi sarcoma-associated herpesvirus (KSHV):
KSHV is another herpes virus transmitted via saliva, sexual contact or blood,
and may be passed from mother to child.
Many
people infected with KSHV have no symptoms, but research has linked the virus
to Kaposi sarcoma and two types of lymphoma.
5. Merkel cell polyomavirus (MCV): MCV is a virus commonly found on the skin.
It
typically causes no symptoms and is thought to be spread via close contact with
the skin or saliva of an infected individual. In some cases, MCV can cause
Merkel cell carcinoma, a type of skin cancer. Dr. Chowdhury explained:
“The
newly discovered virus called Merkel cell virus causes many skin cancers but
prevention of transmission may not be possible because most persons may already
be naturally exposed to this virus and are asymptomatic carriers.
“The persons who have Merkel cell
tumors do not transmit the virus. Avoiding unnecessary exposure to the sun and
receiving periodic skin check-ups are ways to prevent Merkel cell skin cancer.”
“Given
that … there are no vaccines currently available for these five viruses,
prevention strategies to reduce the infections that can lead to cancer are even
more critical,” Linda Birnbaum, Ph.D., director of the National Institute of
Environmental Health Sciences (NIEHS) and National Toxicology Program (NTP),
said in a news release.
“The listings in this report,
particularly the viruses, bring attention to the important role that prevention
can play in reducing the world’s cancer burden.”
“Understanding
the link of viruses to cancer gives us hope for future development of vaccines
and treatments,” Dr. Chowdhury added.
Cancer
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