There are enemies lurking in our society that could be just as deadly as a terrorist attack. They are known as viruses and diseases.
"Over the last 10 decades there have been about 30 newly emerging diseases that have the potential to be pandemics," says Dr. Larry Brilliant, an epidemiologist featured in CNN Films' "Unseen Enemy."
"If we do nothing, it's not a matter of if there will be a global pandemic, it's just a matter of when -- and which virus, and how bad."
Take Zika, for example. The virus first emerged in the Zika forest of Uganda in 1947
. It made headlines in November 2015 when health officials reported a concerning number of babies born in Brazil with microcephaly, a neurological birth defect in which babies are born with abnormally small heads and can have underdeveloped brains.
In 2016, Zika was imported to the US by travelers who were infected while visiting areas where the virus was being transmitted. In July 2016 the first locally transmitted cases in the continental US were reported in Florida and in November 2016 local transmission was confirmed in Texas.
The virus is transmitted primarily by infected mosquitoes and unprotected sex, and can be passed from a pregnant woman to her fetus.
There is currently no vaccine available, but the United Nations health agency released a strategic response plan
to fight the spread of Zika. It focuses on preventing and managing medical complications caused by the infection, which could cost up to $121.9 million, according to the World Health Organization (WHO).
There are several organizations aiding those already infected with the virus and helping others with prevention by providing insect repellant and awareness, in addition to funding for diagnostic tests and vaccines.
Like Zika, mosquitoes of a different type, are the culprit behind malaria.
Typically, malaria causes fever, chills, vomiting and flu-like illness, according to the CDC.
If not treated, it can be deadly.
The disease infects more than 200 million people each year around the globe, killing nearly half a million, according to the World Health Organization. The United Nations Foundation reports
that every 45 seconds a child in Africa dies from malaria.
The global malaria eradication program
set out to make the world malaria-free when it launched in 1955. The campaign helped eliminate the disease from Europe, North America, the Caribbean and parts of Asia and South America, but had virtually no success in sub-Saharan Africa.
Today 80% of those with malaria live in that area. (It is interesting to note that small pox is currently the only disease that has ever been eradicated.)
There are charities responding to malaria by providing insecticide-treated nets and funding to help educate people about the disease.
Even as technology advances and scientific discoveries are made, diseases like malaria and viruses like Zika will undoubtedly strike.
"We are more vulnerable because of our mobility," says Dr. Peter Piot, a microbiologist featured in "Unseen Enemy."
"We are living more and more in very crowded cities. That's fantastic from the perspective of a virus because in no time it can infect hundreds of thousands of people."
But there is a way we can help prevent sickness -- giving everyone access to clean water, according to the CDC.
One billion people do not use drinking water from improved sources. More than 2 billion do not use a sanitary toilet, according to the WHO.
Clean water is essential for drinking, cooking and bathing...for life.
Many organizations have heeded the call and are helping provide clean water by repairing pipes on damaged wells, mobilizing drill rigs and donating tanks that collect and store rainwater that runs off roofs.
You can make an impact on an unseen enemy.