A lot more diseases could be sexually transmitted than we thought

After a team of British researchers found bits of Zika virus lingering in the semen of men whose symptoms had cleared months before, they began to wonder: What other viruses hide out in unsuspecting parts of the body?

At least 27, according to a report published Wednesday by the Centers for Disease Control and Prevention. These include viruses that have been at the center of recent epidemics, like Ebola and Marburg, as well as viruses like mumps and adenovirus, which can cause a version of the common cold.

"This really raises the question of what is the definition of an STD," Fenyong Liu, a professor in the division of infectious diseases at the University of California Berkeley School of Public Health who was not involved with the new report, told Business Insider.

RELATED: 50 cities with the most risk for Zika

51 PHOTOS
50 cities with the most risk for Zika
See Gallery
50 cities with the most risk for Zika

#50. Midland, Texas

Risk level: 1.38

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 161,290

Photo courtesy: Getty

#49. Yuma, Ariz.

Risk level: 1.38

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 203,247

Photo courtesy: Getty

#48. Laredo, Texas

Risk level: 1.38

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 266,673

Photo courtesy: Getty

#47. El Paso, Texas

Risk level: 1.41

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 836,698

Photo courtesy: Getty

#46. Bakersfield, Calif.

Risk level: 1.42

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 874,589

Photo courtesy: Getty

#45. Albuquerque, New Mexico

Risk level: 1.42

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 904,587

Photo courtesy: Getty

#44. Tucson, Ariz.

Risk level: 1.42

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,004,516

Photo courtesy: Getty

#43. Salt Lake City, Utah

Risk level: 1.43

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,153,340

Photo courtesy: Getty

#42. Fresno, Calif.

Risk level: 1.93

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 965,974

Photo courtesy: Getty

#41. Las Vegas, Nev.

Risk level: 1.99

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 2,069,681

Photo courtesy: Getty

#40. Sacramento, Calif.

Risk level: 2

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 2,244,397

Photo courtesy: Getty

#39. San Antonio, Texas

Risk level: 2.03

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 2,328,652

Photo courtesy: Getty

#38. Denver, Colo.

Risk level: 2.2

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 2,754,258

Photo courtesy: Getty

#37. San Diego, Calif.

Risk level: 2.4

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 3,263,431

Photo courtesy: Getty

#36. Phoenix, Ariz.

Risk level: 2.89

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 4,489,109

Photo courtesy: Getty

#35. Montgomery, Ala.

Risk level: 3.92

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 373,141

Photo courtesy: Getty

#34. Huntsville, Ala.

Risk level: 3.94

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 441,086

Photo courtesy: Getty

#33. Shreveport, La.

Risk level: 3.95

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 445,142

Photo courtesy: Getty

#32. Fayetteville, Ark.

Risk level: 3.97

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 501,653

Photo courtesy: Getty

#31. Jackson, Miss.

Risk level: 4

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 577,564

Photo courtesy: Getty

#30. Augusta, Ga.

Risk level: 4

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 583,632

Photo courtesy: Getty

#29. Little Rock, Ark.

Risk level: 4.24

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 729,135

Photo courtesy: Getty

#28. Columbia, SC

Risk level: 4.36

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 800,495

Photo courtesy: Getty

#27. Birmingham, Ala.

Risk level: 4.93

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,143,772

Photo courtesy: Getty

#26. Raleigh, NC

Risk level: 5.09

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,242,974

Photo courtesy: Getty

#25. Richmond, Va.

Risk level: 5.12

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,260,029

Photo courtesy: Getty

#24. Louisville, Ky.

Risk level: 5.13

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,269,702

Photo courtesy: Getty

#23. Oklahoma City, Okla.

Risk level: 5.25

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,336,767

Photo courtesy: Getty

#22. Memphis, Tenn.

Risk level: 5.26

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,343,230

Photo courtesy: Getty

#21. Nashville, Tenn.

Risk level: 6

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,792,649

Photo courtesy: Getty

#20. Kansas City, Mo.

Risk level: 6.04

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 2,071,133

Photo courtesy: Getty

#19. St. Louis, Mo.

Risk level: 6.13

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 2,806,207

Photo courtesy: Getty

#18. Dallas, Texas

Risk level: 7.11

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 500,000-1,000,000
Population: 6,954,330

Photo courtesy: Getty

#17. Charlotte, NC

Risk level: 7.38

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 2,380,314

Photo courtesy: Getty

#16. Washington, D.C.

Risk level: 7.86

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 6,033,737

Photo courtesy: Getty

#15. Philadelphia, Pa.

Risk level: 7.86

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: 10,000-500,000
Population: 6,052,170

Photo courtesy: Getty

#14. Los Angeles, Calif.

Risk level: 7.93

Mosquito level in January: None
Mosquito level in July: Low
Number of people traveling to the U.S. from Zika countries: 500,000-1,000,000
Population: 13,262,220

Photo courtesy: Getty

#13. Savannah, Ga.

Risk level: 7.99

Mosquito level in January: None
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 372,708

Photo courtesy: Getty

#12. Tallahassee, Fla.

Risk level: 7.99

Mosquito level in January: None
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 375,751

Photo courtesy: Getty

#11. Mobile, Ala.

Risk level: 8

Mosquito level in January: None
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 415,123

Photo courtesy: Getty

#10. Charleston, SC

Risk level: 8

Mosquito level in January: None
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 727,689

Photo courtesy: Getty

#9. New Orleans, La.

Risk level: 8.01

Mosquito level in January: None
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,251,849

Photo courtesy: Getty

#8. Atlanta, Ga.

Risk level: 8.13

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: 500,000-1,000,000
Population: 5,614,323

Photo courtesy: Getty

#7. Houston, Texas

Risk level: 8.14

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: 500,000-1,000,000
Population: 6,490,180

Photo courtesy: Getty

#6. Jacksonville, Fla.

Risk level: 8.38

Mosquito level in January: Low
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 1,419,127

Photo courtesy: Getty

#5. New York, NY

Risk level: 8.49

Mosquito level in January: None
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: 1,000,000-2,000,000
Population: 20,092,883

Photo courtesy: Getty

#4. Brownsville, Texas

Risk level: 8.86

Mosquito level in January: Low
Mosquito level in July: Moderate
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 420,392

Photo courtesy: Getty

#3. Tampa, Fla.

Risk level: 9.14

Mosquito level in January: Low
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: <10,000
Population: 2,915,582

Photo courtesy: Getty

#2. Orlando, Fla.

Risk level: 9.43

Mosquito level in January: Low
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: 500,000-1,000,000
Population: 2,321,418

Photo courtesy: Getty

#1. Miami, Fla.

Risk level: 10

Mosquito level in January: Moderate
Mosquito level in July: High
Number of people traveling to the U.S. from Zika countries: 1,000,000-2,000,000
Population: 5,929,819

Photo courtesy: Getty

HIDE CAPTION
SHOW CAPTION
of
SEE ALL
BACK TO SLIDE

The viruses appear to take advantage of one of the body's key protective mechanisms, a phenomenon known as immune privilege. Certain parts of the body, like the eyes, are essentially no-fly zones for the immune system's defense armies. They are shielded from inflammation to protect more critical functions like vision. Similarly, it's believed that some reproductive organs may be immune privileged to protect sperm or eggs.

But this immune privilege may also serve as a foothold for a disease-causing virus like Ebola or Marburg, which the new study finds can remain in human semen for surprisingly long stretches of time. Here, the immune system can't touch them.

In the event of a viral outbreak, physicians and public health experts typically urge people to stay away from anyone who is infected for several weeks, paying particular attention to things like saliva and blood. The new study suggests this may not be enough. In some cases, viruses can persist for as many as 565 days in semen, meaning that an infected person could theoretically remain contagious for up to several months after they come down with one of the viruses.

RELATED: STDs under the microscope

6 PHOTOS
STDs under the microscope: See what they look like
See Gallery
STDs under the microscope: See what they look like
Syphilis is a sexually transmitted infection caused by the spirochete bacterium
Human pap smear showing chlamydia in the vacuoles at 500x and stained with H&E.
Illustration of an infection as a result of the Chlamydia bacterium. Chlamydia trachomatis is responsible for a large part of infertilities, by obstructing the Fallopian tubes, preventing the egg from being fertilised and carried to the uterus.
Gonococcus (neisseria gonorrhoeae) is the bacterium responsable for gonorrhea. In men the symptoms are acute burning when urinating and some discharge (clap). In women the symptoms are burning when urinating, bartholin's cyst, cervisitis, salpingitis.
HIV infection. Computer artwork of HIV particles in the bloodstream.
HIDE CAPTION
SHOW CAPTION
of
SEE ALL
BACK TO SLIDE

"Clinicians and researchers need to consider the possibility that traditionally ‘non-sexually transmitted’ viruses can persist in semen, and this therefore raises the possibility of sexual transmission," Alex Salam, the lead author on the paper and a clinician and clinical researcher for the United Kingdom Public Health Rapid Support Team, told Business Insider.

Although the researchers found pieces of the genetic material of these viruses, including Lassa fever, Epstein-Barr, and varicella zoster (the virus that causes the chicken pox), that doesn't necessarily mean that the virus could be transmitted sexually. To find out if that is the case, they'll need more research.

In the past, it was unclear how several viruses on the list could spread. BK virus, for example, was thought to spread from person to person through respiratory fluids or urine, but the new study suggests that it can also be passed on through semen.

"This should raise people's awareness that even though they might contract a respiratory illness or something that effects the lungs, it could potentially be spread through an entirely different part of the body like the semen," said Liu.

To come up with their list, researchers combed the scientific literature and found nearly 4,000 published papers that documented evidence of viruses whose genetic material had ended up in semen.

In addition to the 27 viruses they found, the researchers also discovered the genetic material of several other viruses, such as dengue, SARS, and smallpox, in human testes. There isn't enough evidence yet to say if these viruses would also be present in semen, however.

Lots of questions about the viruses remain. The most pressing is whether or not they could all be sexually transmitted to a new host. The researchers also want to know how long the viruses remain in semen and in what concentrations, as well as how their presence might impact sperm and male fertility more broadly.

"This brings up more questions than it answers — and that's fascinating," Liu said.

More from Business Insider:

Read Full Story