Diseases & Conditions
Cholera is an acute, diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae. An estimated 3-5 million cases and over 100,000 deaths occur each year around the world. The infection is often mild or without symptoms, but can sometimes be severe. Approximately one in 10 (5 to 10 percent) infected persons will have severe disease characterized by profuse watery diarrhea, vomiting, and leg cramps. In these people, rapid loss of body fluids leads to dehydration and shock. Without treatment, death can occur within hours.
Dengue fever is an infectious disease carried by mosquitoes and caused by any of four related dengue viruses. This disease used to be called "break-bone" fever because it sometimes causes severe joint and muscle pain that feels like bones are breaking. Health experts have known about dengue fever for more than 200 years.
Escherichia coli (E. coli) bacteria live in the intestines of people and animals, and are key to a healthy intestinal tract. Most E. coli strains are harmless, but some can cause diarrhea through contact with contaminated food or water while other strains can cause urinary tract infections, respiratory illness and pneumonia.
Ebola virus disease, first recognized in 1976 in the Democratic Republic of the Congo, is a serious and often fatal illness in humans and nonhuman primates caused by infection with one of five Ebola virus species (four of which can infect humans). The virus is spread through direct contact with the bodily fluids of a sick person and can cause fever, headache, muscle pain, weakness, fatigue, diarrhea, vomiting, stomach pain and hemorrhage (severe bleeding).
Fungal diseases are caused by a wide variety of fungi that are commonly found in the environment. Invasive fungal infections rarely occur in healthy people, but fungi can cause serious infections in individuals with weakened immune systems.
Gonorrhea is a sexually transmitted disease that can infect both men and women. Caused by the Neisseria gonorrhoeae bacterium, gonorrhea can cause infections in the genitals, rectum and throat. Although treatable, drug-resistant forms of gonorrhea are increasing.
Group A streptococcal (GAS) infections can range from a mild skin infection or a sore throat to severe, life-threatening conditions. Most people are familiar with strep throat, which along with minor skin infections, is the most common form of the disease.
Hepatitis is an inflammation of the liver. Viruses are the most common cause of hepatitis, but the condition can also be caused by other infections, heavy alcohol use, toxins, certain medications, and autoimmune disease. There are five main virus types that cause hepatitis---type A, B, C, D and E. Hepatitis A and E are typically caused by ingesting contaminated food or water. Type B commonly occurs through contact with infected blood, semen or other bodily fluid through sex, sharing needles or other drug-injection equipment or from mother to baby at birth.
HIV, or human immunodeficiency virus, is the virus that causes AIDS (Acquired Immunodeficiency Syndrome). HIV attacks the immune system by destroying CD4 positive (CD4+) T cells, a type of white blood cell that is vital to fighting off infection. The destruction of these cells leaves people living with HIV vulnerable to other infections, diseases and other complications. As the leading U.S. government institute for HIV/AIDS research, NIAID is committed to conducting the research necessary to successfully end the fight against HIV/AIDS.
Influenza, or flu, is a contagious respiratory infection caused by several flu viruses that infect the nose, throat and lungs. People infected with the seasonal flu virus feel miserable with fever, chills, muscle aches, coughing, congestion, headache and fatigue for a week or so. Most people who get the flu get better within two weeks, but some people may develop serious complications, such as pneumonia. Pandemic influenza is when a new flu virus strain occurs that can spread easily from person-to-person and the virus is one for which most people have no immunity.
Leishmaniasis is a parasitic disease transmitted by the bites of infected sand flies. It is found in nearly 88 countries, from rain forests in Central and South America to deserts in the Middle East and west Asia. Some cases of the disease have also appeared in Mexico and Texas. The disease takes several different forms, including the most common cutaneous leishmaniasis, which causes skin sores, and the more severe visceral leishmaniasis (also known as kala azar), which affects internal organs such as the spleen, liver, and bone marrow.
Leprosy (Hansen's Disease) is a chronic infectious disease that primarily affects the peripheral nerves, skin, upper respiratory tract, eyes, and nasal mucosa (lining of the nose). The disease is caused by a bacillus (rod-shaped) bacterium known as Mycobacterium leprae.
Lyme disease, or borreliosis, is caused by the bacterium Borrelia burgdorferi and is transmitted to humans through the bite of an infected blacklegged deer tick. It is the most common tickborne infectious disease in the United States.
Malaria is a mosquito-borne disease that can cause infected people to become very sick with high fever, chills, and flu-like illness. It can also cause death. Substantial progress has been made globally to control and eliminate malaria, but it continues to be a significant public health problem with roughly 3.2 billion people worldwide at risk for the disease.
Middle East Respiratory Syndrome (MERS-CoV) is a viral respiratory illness that was first reported in Saudi Arabia in 2012 and has since spread to several other countries. Most people infected with MERS-CoV developed severe acute respiratory illness, including fever, cough, and shortness of breath; many of them died. Severe acute respiratory syndrome (SARS-CoV), also a severe viral respiratory illness, was first reported in Asia in February 2003 and spread to dozens of countries before being contained. Since 2004, there have been no known SARS cases.
Pertussis, also known as whooping cough, is a highly contagious respiratory disease. It is caused by the bacterium Bordetella pertussis. Pertussis is known for uncontrollable, violent coughing that often makes it hard to breathe. After fits of many coughs, someone with pertussis often needs to take deep breaths, which result in a “whooping” sound.
Plague, caused by the bacterium Yersinia pestis, is a disease that affects humans and other mammals. People typically get infected after being bitten by a rodent flea that is carrying the bacterium or by handling a plague-infected animal. Although the disease killed millions in Europe during the Middle Ages, antibiotics effectively treat plague today. Without prompt treatment, plague can cause serious illness or death. Human plague infections continue to occur in the western United States, but significantly more cases occur in parts of Africa and Asia.
Prion diseases are a related group of rare, fatal brain diseases that affect animals and humans. Also known as transmissible spongiform encephalopathies (TSE), they include bovine spongiform encephalopathy ("mad cow" disease) in cattle; Creutzfeldt-Jakob disease in humans; scrapie in sheep; and chronic wasting disease in deer and elk.
Respiratory syncytial virus, or RSV, is a respiratory virus that infects the lungs and breathing passages. Healthy people typically experience mild, cold-like symptoms and recover in a week or two. However, RSV can be serious, particularly for infants and the elderly. RSV is the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia in children younger than 1 year of age in the United States.
Rocky Mountain spotted fever is a tickborne disease first recognized in 1896 in the Snake River Valley of Idaho. It was originally called “black measles” because of the look of its rash in the late stages of the illness, when the skin turns black. It was a dreaded, often fatal disease, affecting hundreds of people in Idaho. By the early 1900s, the disease could be found in Washington, Montana, California, Arizona, and New Mexico.
Schistosomiasis, also known as bilharzia, is a neglected tropical disease caused by parasitic worms. It is second only to malaria as the most devastating parasitic disease. The parasites that cause schistosomiasis live in certain types of freshwater snails. The infectious form of the parasite emerge from the snail and then contaminate the water. People become infected when their skin comes into contact with the contaminated freshwater. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum.
Sexually transmitted diseases (STDs) are infections transmitted from an infected person to an uninfected person through sexual contact. STDs can be caused by bacteria, viruses, or parasites. Examples include gonorrhea, genital herpes, human papillomavirus infection, HIV/AIDS, chlamydia, and syphilis.
Shigellosis is an infectious, diarrheal disease caused by a group of bacteria called Shigella. It is transmitted via contact with contaminated food, water, surfaces or an infected person. The disease typically resolves in 5 to 7 days. Shigella causes roughly 500,000 cases of diarrhea in the United States each year.
Smallpox, caused by the variola virus, was a highly contagious infectious disease that caused infected individuals to develop a fever and a progressive, disfiguring skin rash. Three of out 10 individuals infected with smallpox died. Many survivors have permanent scars, often on their faces, or were left blind. Through vaccination, the disease was eradicated in 1980. However, research for effective vaccines, drugs and diagnostics for smallpox continues in the event it is used as a bioterror weapon.
Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum. It is transmitted from person to person via direct contact with a syphilitic sore, known as a chancre. These sores can be found on the genitals, vagina, anus, rectum, lips and mouth. Pregnant women can transmit the disease to their unborn child. Syphilis can cause long-term health complications if left untreated.
Tickborne diseases are becoming a serious problem in the United States as people increasingly build homes in formerly uninhabited wilderness areas where ticks and their animal hosts live. Tickborne diseases can be caused by viruses, bacteria, or parasites. Most people become infected through tick bites during the spring and summer months.
Tuberculosis (TB) is a contagious disease caused by infection with Mycobacterium tuberculosis (Mtb) bacteria. It is spread through the air when a person with TB disease of the lungs or throat coughs, speaks or sings, and people nearby breathe in these bacteria and become infected.
West Nile virus (WNV), a mosquito-borne illness, first emerged in the Western Hemisphere in 1999 in the New York City area and has since spread across the United States. Most people infected with WNV will have no symptoms. About 1 in 5 people infected will develop a fever with other symptoms. Less than 1 percent of those infected will develop a serious, sometimes fatal, neurologic illness.
Discovered in the Zika forest, Uganda, in 1947, Zika virus is a member of the flavivirus family. Other flaviviruses include those that cause dengue, yellow fever, and West Nile fever. Like its relatives, Zika virus is primarily transmitted to humans through the bite of infected Aedes aegypti mosquitoes. Zika virus can be transmitted from an infected pregnant woman to her baby during pregnancy and can result in serious birth defects, including microcephaly. Less commonly, the virus can be spread through intercourse or blood transfusion.