The Ebola virus has now killed more than 1,000 people in West Africa. Although the mortality rate of the most recent outbreak isn't as high as in previous events, it's still the case that most people who become infected with Ebola will not survive. (The mortality rate is about 60 percent for the current outbreak, compared with 90 percent in the past, according to the National Institutes of Health.)
But despite this somber prognosis, health experts in the United States aren't particularly worried about the threat of Ebola in this countryor in other developed countries.
Rabies
Over the past 100 years, rabies has declined significantly as a public health threat in the United States, according to the Centers for Disease Control and Prevention. Approximately two people now die yearly in the United States from this virus, which is transmitted to people through saliva when they are bitten by infected animals, such as dogs or bats.
People who know they have been bitten by an animal should receive the rabies vaccine, which prevents infection by the virus, according to the CDC. But, especially in the case of bat bites, people may not always realize they have been bitten.
And rabies has one of the highest fatality rates of any virus; only three people in the United States are known to have ever survived the disease without receiving the vaccine after exposure to the virus.
Still, the disease remains a greater threat in other areas of the world than in the United States. Approximately 55,000 people die of rabies every year in Africa and Asia, according to the WHO.
HIV
Though the number of annual deaths related to human immunodeficiency virus (HIV) has declined in recent years, an estimated 1.6 million people worldwide died of HIV and acquired immune deficiency syndrome (AIDS) related causes in 2012, according to the WHO. The virus attacks a person's immune cells and weakens the immune system over time, making it very difficult for the infected individual to fight off other diseases.
About 15,500 people with an AIDS diagnosis died in 2010 in the United States, according to the CDC. In total, an estimated 650,000 people have died of AIDS in the United States since the disease was discovered in 1981. An estimated 36 million people have died worldwide from the epidemic.
Today, people with HIV do live longer than they used to, a trend that coincides with the increased availability of antiretroviral therapy, as well as the decline in new infections since the peak of the AIDS epidemic in 1997. However, no cure for HIV exists.
Influenza
The flu may not sound very scary, but it kills far more people every year than Ebola does. The exact number of people who die each year from seasonal flu virus is the subject of much debate, but the CDC puts the average number of annual deaths in the United States somewhere between 3,000 and 49,000.
The large variation in yearly deaths arises because many flu deaths are not reported as such, so the CDC relies on statistical methods to estimate the number. Another reason for this wide range is that annual flu seasons vary in severity and length, depending on what influenza viruses are most prominent. In years when influenza A (H3N2) viruses are prominent, death rates are typically more than double what they are in seasons when influenza A (H1N1) or influenza B viruses predominate, according to the CDC.
A highly contagious virus, influenza sickens far more people than it kills, with an estimated 3 million to 5 million people becoming seriously ill yearly from influenza viruses. Worldwide, the flu causes an estimated 250,000 to 500,000 deaths every year, according to the World Health Organization (WHO).
Despite the relatively low mortality rate of the virus, public health professionals and doctors recommend annual flu shots to keep the risk of complications from influenza at bay.
"Healthy people should get their vaccines every year," Rokusek told Live Science. "Studies have shown that the flu vaccine is an effective preventative measure."
But flu vaccines, which offer immunity from influenza A and B viruses, do not protect against other forms of influenza, which can arise when the virus undergoes genetic changes. New strains of the flu result in higher than average mortality rates globally. The most recent influenza pandemic, the "swine flu" or H1N1 pandemic, killed between 151,700 and 575,400 people globally during 2009 and 2010, according to the CDC.
Mosquito-borne viruses
Spread through the bite of an infected mosquito, viruses such as dengue, West Nile and yellow fever kill more than 50,000 people worldwide every year, according to estimates by the WHO and the CDC. (Malaria — which is also spread by mosquitos, but is caused by a parasite rather than a virus — kills more than 600,00 people yearly.)
At least 40 percent of the world's population, or about 2.5 billion people, are at risk of serious illness and death from mosquito-borne viral diseases, according to the CDC.
Dengue fever, which is endemic to parts of South America, Mexico, Africa and Asia, claims approximately 22,000 lives every year, according to the CDC. Dengue hemorrhagic fever is a deadly infection that causes high fevers and can lead to septic shock.
These diseases occur in regions neighboring the United States, making them a threat in this country.
"Dengue is very active in the Caribbean, and travelers to the Caribbean come back to the United States with dengue," said Dr. Robert Leggiadro, a New York physician and professor of biology at Villanova University in Pennsylvania. [10 Deadly Diseases That Hopped Across Species]
People infected with dengue while traveling abroad can spread the disease at home when mosquitos bite them, and then bite other people, Leggiadro said.
Even more deadly than dengue is yellow fever, which mostly affects people in Latin America and Africa. The disease causes an estimated 30,000 deaths worldwide, according to the WHO.
Less deadly, but still dangerous is West Nile virus, a viral neurological disease that is spread by mosquitos that bite humans after feasting on birds infected with the virus. Although the vast majority of people infected with this virus will not show symptoms of West Nile, the disease has killed an estimated 1,200 people in the United States since it was first seen here in 1999, according to the CDC.
Rotavirus
Not everyone is at high risk of contracting rotavirus, but for children around the world, this gastrointestinal virus is a very serious problem. Approximately 111 million cases of gastroenteritis caused by rotavirus are reported every year globally, according to the CDC. The vast majority of those affected by the virus are children under the age of 5, and about 82 percent of deaths associated with the virus occur in children in developing nations.
Globally, an estimated 440,000 children who contract the virus die each year from complications, namely dehydration. In the United States, a vaccine for rotavirus was developed in 1998, but was later recalled due to safety concerns. A newer vaccine, developed in 2006, is now available and is recommended for children ages 2 months and older.
Despite routine vaccinations for rotavirus in the United States, the CDC estimates that between 20 and 60 children under age 5 die every year from untreated dehydration caused by the virus.
While some parents in the United States have expressed concern about the complications that may arise as a result of vaccinating for rotavirus, Leggiadro told Live Science that vaccination for this and other preventable diseases is the best way to safeguard against diseases that, if left untreated, can be deadly.
