JULY/AUGUST 2019. DISCOVER 39
Bacteriophages:
Good Guy Viruses
Bacteriophages, bacteria-killing
viruses that look like lunar landers,
have already played an important role
in scientific research. In 1976, phage
MS2 was the first organism to have
its genome — a mere four genes
— sequenced. In the future,
they may help us fightantibiotic-resistant
bacteria.
Spotlighting (In)famous Viruses
Influenza: Several strains of this virus circulate worldwide
each year, mutating as they travel. The 2017-18 flu season
affected 49 million Americans and claimed 79,000 lives,
according to the CDC.
Ebola: The Ebola virus attacks cells in the immune system,
prompting them to produce chemicals that damage blood
vessels and trigger coagulation; during an outbreak, the
virus can kill half of the people infected, sometimes more.
Hepatitis B: The virus attacks the liver’s hepatocytes
and can lead to debilitating symptoms such as fatigue,
cancer and even death.
HIV: The virus behind the AIDS epidemic targets human
immune cells called T-helpers, leaving its host with
compromised defenses and extra vulnerable to diseases
from other pathogens, such as pneumonia.
RSV: Respiratory syncytial virus is responsible for over
2 million doctor visits every year in the U.S. — and that’s
just for children under 5. The virus causes mild coldlike
symptoms, though serious cases, especially in infants and
the elderly, can lead to pneumonia or bronchiolitis.
HPV: Human papillomavirus, a sexually transmitted virus, can
greatly increase your risk for certain cancers. It’s estimated
that most unvaccinated, sexually active adults carry some
form of the virus, though not every infection will trigger host
cells to multiply out of control.
Zika: Related to other mosquito-borne viruses including
dengue and West Nile, Zika was first identified in the 1940s
and can cause catastrophic damage to developing fetuses.
As climate change allows tropical insects to expand their
range, Zika’s prevalence worldwide will likely increase.
Viral Events of the Modern Era
1952 Smallpox is eradicated in U.S.
1978 Smallpox is eradicated worldwide.
1979 Widespread vaccination eliminates polio in the U.S., though it persists
in other countries.
1982 A new viral-induced immunodeficiency disorder is named: AIDS.
1995 AIDS deaths in the U.S. peak.
2003 SARS (severe acute respiratory syndrome) hits. Over 8,000 cases
are reported, and the virus claims 774 lives, mostly in China.
2009 H1N1, also known as swine flu, kills over 150,000 worldwide.
2015 Measles outbreak is linked to unvaccinated Disneyland visitors.
2019 Another measles outbreak, which began in the Pacific Northwest,
infects more than 700 people across 22 states by late April.How the Body Protects Itself
When the human body detects a viral intruder, the immune
system’s white blood cells go to war. The first line of defense
includes macrophages, large cells that gobble up as many viruses
as they can. If that battle is lost and the viruses take hold, the
second wave is led by T and B lymphocytes. On the signal from the
T cells, these B cells make antibodies, special proteins that latch
onto the viruses, marking them for destruction by other immune
cells and sometimes preventing them from replicating. T and B
cells never forget a virus they’ve encountered, so they jump into
action if the virus reappears.
T and B cells aren't as much help against colds or the flu,
however. The “common cold” can be caused by a number of viruses,
including adenovirus or rhinovirus: If you’ve had a cold more than
once, it means you’ve been attacked by a different virus or viral
strain each time.
The influenza virus has many different strains, including
several that quickly mutate beyond recognition by your T and
B cells. Epidemiologists monitor the circulation and evolution
of different strains worldwide and determine those most likely
to pose a threat during the next flu season. That's why flu shots
change every year.