Infectious Diseases

An infectious disease is a clinically evident disease resulting from the presence of pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular parasites and aberrant proteins known as prions. These pathogens are able to cause disease in animals and/or plants.

Infectious pathologies are usually qualified as contagious diseases (also called communicable diseases) due to their potentiality of transmission from one person or species to another. Transmission of an infectious disease may occur through one or more of diverse pathways including physical contact with infected individuals. These infecting agents may also be transmitted through liquids, food, body fluids, contaminated objects, airborne inhalation, or through vector-borne spread.

An infection however, is not synonymous with an infectious disease, as an infection may not cause important clinical symptoms or impair host function.

AIDS/HIV

Human immunodeficiency virus, or HIV, is the retrovirus that causes acquired immune deficiency syndrome (AIDS). The syndrome was first recognized in 1981. The virus weakens a person's ability to fight infections and cancer. People with HIV are said to have AIDS when they develop certain infections or cancers or when their CD4 count is less than 200. CD4 count is determined by a blood test in a doctor's office.

Having HIV does not always mean that you have AIDS. It can take many years for people with the virus to develop AIDS. HIV and AIDS cannot be cured. An entire HIV regimen that was once complex, involving multiple agents (20 to 40 pills and capsules) taken at different times of the day is now as compact and simple as one pill, once a day. Twenty-five percent of individuals in the US with HIV do not know their status. They often present very late in disease. There are over 40,000 new infections annually in the U.S.. The HIV positive but unaware individuals account for about 54 to 70 percent of the new infections. The Centers for Disease Control recognizes the significant benefits to an individual in terms of decreased morbidity and mortality when therapy is initiated earlier in disease and the potential to reduce ongoing HIV transmission. The CDC now recommends that HIV testing be incorporated into routine health care for all individuals.

Cholera

Cholera is an acute infectious disease caused by the bacterium Vibrio cholerae, which lives and colonizes in the small intestine but does not destroy or invade the intestinal tissue. The major symptom of cholera is massive watery diarrhea that occurs because the bacteria’s toxin stimulates the small intestine to secret fluid. There are several strains of V. cholerae and the severity of the disease is based on the particular infectious strain. Cholera is not a difficult disease to treat and most people recover well with hydration. However, if the disease goes untreated, it can rapidly lead to shock, as a result of fluid and electrolyte loss and to life-threatening complications.

Common Cold

Sneezing, scratchy throat, runny nose—everyone knows the first signs of a cold, probably the most common illness known. People in the United States suffer 1 billion colds each year, according to some estimates. According to the Centers for Disease Control and Prevention (CDC), 22 million school days are lost annually in the United States due to the common cold.

Cytomegalovirus (CMV) Infection

Cytomegalovirus infection (CMV) is a viral infection that rarely causes obvious illness in the immunocompetent. The virus that causes CMV is part of the herpes virus family and, like other herpes viruses, may become dormant for a period of time and then be reactivated. Physicians recognize three clinical forms of CMV. These include: (1) CMV inclusion disease of the newborn, which ranges in severity from being without symptoms to being a severe disease affecting the liver, spleen and central nervous system, with possible developmental disabilities; (2) Acute acquired CMV infection, which is similar to infectious mononucleosis and characterized by fever, a feeling of being not quite right (malaise), skeletal-muscular pain and the absence of a sore throat; (3) CMV in immunocompromised persons (for instance, people who have had organ transplants or who have HIV) with increased risk for difficult eye infections (CMV retinitis), gastrointestinal CMV and encephalitis. Therapy is available for both prevention and treatment of CMV. According to the Centers for Disease Control and Prevention, about 40,000 children are born with congenital CMV infection.

Diphtheria, Tetanus and Pertussis Vaccines

Diphtheria, tetanus and pertussis (usually called “whooping cough”) are all dangerous infectious diseases caused by bacteria (different bacteria are responsible for each infection).

The major symptoms of diphtheria include sore throat and swollen glands, as well as the characteristic grayish material that coats the back of the throat and may make breathing difficult. The bacteria produce toxins that damage the heart, brain and nerves, ultimately leading to death if not treated. The bacteria responsible for tetanus also produce a toxin that affects the nerves. This can lead to muscle stiffness and spasms, especially in the face and neck muscles (which will cause “lock jaw,” the condition most people associate with tetanus). Even with treatment, tetanus can be fatal.

Pertussis is better known as whooping cough. This is because the major symptom is violent coughs, followed by a “whoop” sound as the patient struggles to breathe in. The coughing spells can be so powerful that they result in broken ribs, vomiting and broken blood vessels in the face.

Whooping cough used to be the leading cause of childhood illness in the U.S. and diphtheria used to be a leading cause of death in children. Tetanus was also alarmingly prevalent. Thankfully, all three diseases have become quite rare in the U.S. since immunization became routine.

Ear Infection

Middle ear infections are one of the most common childhood problems. A small tube connects the ear to the throat. A cold can cause this tube to swell. When the tube swells enough to become blocked, it can trap fluid inside the ear. This makes it a perfect place for germs to grow and cause an infection. Three out of four children experience otitis media, or ear infection, by the time they are three years old.

Epstein-Barr Virus (EBV) Infection

Epstein-Barr Virus, more commonly known as Mono, is a double-stranded DNA virus in the herpes family of viruses. Infection with EBV is characterized by fatigue and general malaise. Infection with EBV is fairly common and is usually a transient and minor thing. However, in some individuals EBV can trigger chronic illness, including immune and lymphoproliferative syndromes. It is a particular danger to people with compromised immune systems, such as from AIDS. EBV was at one time believed to be the cause of the chronic fatigue syndrome, but chronic infection with this virus actually produces a separate (if similar) disorder. According to the National Center for Infectious Diseases, In the United States as many as 95 percent of adults between 35 and 40 years of age have been infected.

Fever

Fever is a frequent medical symptom that describes an increase in internal body temperature to levels above normal. Fever is a common symptom of many medical conditions.

Fungal Infections

Fungal infections have recently emerged as a growing threat to human health, especially in persons whose immune systems are compromised in some way. Clinicians are particularly concerned that the increasing use of antifungal drugs will lead to drug-resistant fungi, especially in settings such as hospitals where hospital-acquired infections are a growing problem.

Genital Warts

Human papillomavirus (HPV) is one of the most common causes of sexually transmitted infection (STI) in the world. Health experts estimate there are more cases of genital HPV infection than any other STI in the United States. According to the Centers for Disease Control and Prevention (CDC), approximately 6.2 million new cases of sexually transmitted HPV infections are reported every year. At least 20 million people in this country are already infected.

Helminthic Infestations

Parasitic worms or helminths are a division of eukaroytic parasites that, unlike external parasites such as lice and fleas, live inside their host. They are worm-like organisms that live and feed off living hosts, receiving nourishment and protection while disrupting their hosts' nutrient absorption, causing weakness and disease. Those that live inside the digestive tract are called intestinal parasites.

Hepatitis

Viral hepatitis is inflammation of the liver caused by a virus. Hepatitis may start and resolve quickly (acute hepatitis), or cause long-term disease (chronic hepatitis). In some instances, progressive liver damage, liver failure, or even liver cancer may result. There are five identified types of viral hepatitis and each one is caused by a different virus. In the U.S., hepatitis A, hepatitis B and hepatitis C are the most common types. Hepatitis A can be prevented with immunization. Hepatitis B immunization is now recommended for infants, children, health care workers and at risk adults. Only Hepatitis B (CHB) and hepatitis C (CHC) cause ongoing chronic disease. There are 400 million individuals worldwide with CHB and 200 million with CHC. Seventy five percent of those with CHB are of Asian Pacific Islander origin. Approximately 25 to 40 percent of those with chronic disease will go on to develop end stage liver disease of hepatocellular carcinoma. There are close to two million in the US with CHB and five million with CHC. Chronic viral hepatitis accounts for the majority of liver transplants in the U.S. Therapy is available for both CHB and CHC. Broader screening could identify individuals earlier in the course of disease.

Herpes Simplex Virus Infection

Herpes Simplex Virus infection (HSV) is a viral infection of the skin and or mucous membranes manifested by painful, blister-like lesions on a red base most often on the mouth or face (oral herpes) or in the genital area (genital herpes).

Infection

An infection occurs when a foreign species colonizes itself in a host organism. The invader (or pathogen) uses the host’s body to multiply, which may interfere with the normal body function of the host. These pathogens can be bacteria, parasites, fungi, viruses, prions, or viroids. An infection can lead to chronic wounds, gangrene and even death. After the host body’s immune system determines that there has been an infection, an immune response kicks in and inflammation and superficial redness generally ensue. In some cases a parasitic relationship develops between the host and the parasite where the parasite benefits to the detriment of the host. There are cures for many infectious diseases; however many preventable infections cause death in developed and developing countries alike.

Influenza

Influenza - commonly shortened to "the flu" - is an extremely contagious viral disease that appears most frequently in winter and early spring. The infection spreads through the upper respiratory tract and sometimes invades the lungs. Although both colds and influenza stem from viruses that infect the upper respiratory tract, the symptoms of influenza are more pronounced and its complications more severe. The first flu virus was identified in the 1930s. Since then, scientists have classified influenza viruses into types A, B, and C. Type A is the most common and usually causes the most serious epidemics. Type B outbreaks also can cause epidemics, but the disease it produces generally is milder than that caused by type A. Type C viruses, on the other hand, never have been connected with a large epidemic. Despite advances in prevention and treatment, influenza and its complications are still fatal to about 36,000 people in the U.S. annually

Malaria

Malaria is an infection of the blood that is carried from person to person by mosquitoes. The disease has been recognized for thousands of years and once was found almost everywhere except in the most northern areas of the world. Malaria has been wiped out in North America, Western Europe and Russia. It remains a serious problem in much of the tropical and subtropical world. According to the National Institute of Allergy and Infectious Diseases, more than 40 percent of the world’s population lives in areas where there is a risk for contracting malaria.

Measles

Measles is a highly contagious viral infection spread through respiration, either with contact with an infected person’s fluids or through a cough. The disease is extremely rare in the U.S. because of widespread immunization programs. Measles is transmitted when an infected person coughs or sneezes. The virus is most often spread when people first become ill and before they know they have the disease. A person is contagious from about four days before the rash breaks out to four days after the rash appears.

Meningococcal Infections (Meningitis)

Meningococcal meningitis is a form of meningitis caused by a specific bacterium known as Neisseria meningitidis. Meningitis is characterized by inflammation of the membranes around the brain or spinal cord. This inflammation can begin suddenly or develop gradually. Symptoms may include fever, headache and a stiff neck, sometimes with aching muscles. Nausea, vomiting and other symptoms may also occur. Skin rashes occur in about half of all individuals with meningitis. There were about 25,000 incidences of the disease in 2006.

Mumps

Mumps is a contagious viral infection that can cause painful swelling of the parotid glands, which are the salivary glands located between the ear and the jaw. Mumps can affect many body systems and cause flu-like symptoms, abdominal pain, swollen cheeks and swollen and painful testicles. However, up to 20 percent of people who are infected with the mumps virus do not have any symptoms. Mumps is spread when an infected person coughs or sneezes, as well as through contact with recently contaminated items such as tissues, drinking glasses and dirty hands.

Pneumonia

Pneumonia is frequently but not always due to infection, causing one or both lungs to become inflamed. The infection may be bacterial, viral, fungal or parasitic. Symptoms may include fever, chills, cough, chest pain and shortness of breath. Pneumonia can be contracted in daily life, such as at school or work. This is called community-based pneumonia. Someone can also get it when they are in a hospital or nursing home. This is called hospital-based pneumonia. It may be more severe when the person is already ill.

Polio

Polio (poliomyelitis) is a viral illness that damages nerves that control muscles, resulting in muscle weakness. In severe illnesses, a person can lose the ability to move both arms and legs (paralysis) and may be unable to breathe without help. Symptoms of polio include: headache, sudden fever, sore throat, neck and back stiffness, muscle weakness and pain. Polio is now rare in developed countries because most children receive immunization against the virus.

Rabies

Rabies is a disease caused by a virus that can affect the central nervous system (brain and spinal cord) of any kind of mammal, including humans. Rabid animals can spread the disease through their saliva or brain matter. People who get rabies are almost always exposed from a bite from a rabid animal. Because of widespread animal vaccination programs, people in the U.S. rarely get rabies: it is more common in developing nations. According to the World Health Organization there are about 55,000 human deaths worldwide.

Rubella

Rubella, also called German measles or three-day measles, is a disease caused by the rubella virus. Rubella is generally a mild illness that does not result in long-term problems. The rubella virus is most often spread through droplets of fluid from the mucous membranes that contain the virus. An infected person can spread these droplets by coughing, sneezing, talking, or sharing food and drinks. One can become infected by touching a surface contaminated with the droplets and then touching the eyes, nose, or mouth before washing the hands.

Sinusitis

Sinusitis is the infection or inflammation of the sinuses. Health experts estimate 37 million Americans are affected by sinusitis every year. Healthcare providers report nearly 32 million cases of chronic sinusitis to the Centers for Disease Control and Prevention annually. Americans spend $5.8 billion each year on healthcare costs related to sinusitis.

Shingles

Shingles (herpes zoster) is an outbreak of rash or blisters on the skin that is caused by the same virus that causes chickenpox — the varicella-zoster virus. It occurs in 1.2 to 3.4 per 1,000 individuals each year.

Tuberculosis

Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis, a slow-growing bacteria that thrives in areas of the body that are rich in blood and oxygen, such as the lungs, but can spread to other parts of the body. TB in the lungs is easily spread to other people through coughing or laughing. According to the National Institute of Allergy and Infectious Disease, in 2006 9.2 million new cases of TB emerged.

Typhoid

An acute illness with fever caused by infection with the Salmonella typhi bacteria, typhoid fever is contracted from contaminated water and food. The disease has an insidious onset characterized by fever, headache, constipation, malaise, chills and muscle pain. Confusion, delirium, intestinal perforation and death may occur in severe cases. In the United States about 400 cases occur each year, and 75 percent of these are acquired while traveling internationally. Typhoid fever is still common in the developing world, where it affects about 21.5 million persons each year.

Urinary Tract Infections

An infection in the urinary system that begins when microorganisms cling to the opening of the urethra (the canal from the bladder) and begin to multiply, a urinary tract infection is mostly due to one type of bacteria - E. coli. The infection can be prevented by drinking plenty of fluids and practicing good hygiene, especially after sexual intercourse.

Viral Infections

The successful invasion, establishment and growth of viruses in the tissues of the host. Viral infections are hard to treat because viruses live inside the body's cells. They are "protected" from medicines, which usually move through the bloodstream. Antibiotics do not work for viral infections. There are a few antiviral medicines available. Vaccines can help prevent one from getting many viral diseases.

Yellow Fever

Yellow fever is a viral disease that is transmitted to humans through the bite of infected mosquitoes. Illness ranges in severity from an influenza-like syndrome to severe hepatitis and hemorrhagic fever. Yellow fever virus (YFV) is maintained in nature by mosquito-borne transmission between nonhuman primates. Transmission by mosquitoes from one human to another occurs during epidemics of “urban yellow fever.” During silent periods it occurs in 1.4 to 2.4 per 1,000 people.