Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
PCR (polymerase chain reaction) is a method to analyze a short sequence of
DNA (or RNA) even in samples
containing only minute quantities of DNA or RNA. PCR is used to reproduce
(amplify) selected sections of DNA or RNA. Previously, amplification of DNA involved cloning the segments of interest into vectors for
expression in bacteria, and took
weeks. But now, with PCR done in test tubes, it takes only a few hours. PCR is
highly efficient so that untold numbers of copies can be made of the DNA.
Moreover, PCR uses the same molecules that nature uses
for copying DNA:
Two "primers", short single-stranded DNA sequences that are synthesized to
correspond to the beginning and ending of the DNA stretch to be copied;
An enzyme called polymerase that moves along the segment of DNA, reading
its code and assembling a copy; and
A pile of DNA building blocks that the polymerase needs to make that copy.
How is PCR (polymerase chain reaction) done?
As illustrated in the
animated picture of PCR, three major steps
are involved in a PCR. These three steps are repeated for 30 or 40 cycles. The
cycles are done on an automated cycler, a device which rapidly heats and cools
the test tubes containing the reaction mixture. Each step -- denatauration
(alteration of structure), annealing (joining), and extension -- takes place at
a different temperature:
Denaturation: At 94 C (201.2 F), the double-stranded DNA melts and opens into two
pieces of single-stranded DNA.
Annealing: At medium temperatures, around 54 C (129.2 F), the primers pair up
(anneal) with the single-stranded "template" (The template is the sequence of
DNA to be copied.) On the small length of double-stranded DNA (the joined primer
and template), the polymerase attaches and starts copying the template.
Extension: At 72 C (161.6 F), the polymerase works best, and DNA building blocks
complementary to the template are coupled to the primer, making a double
stranded DNA molecule.
With one cycle, a single segment of double-stranded DNA template is amplified
into two separate pieces of double-stranded DNA. These two pieces are then
available for amplification in the next cycle. As the cycles are repeated, more
and more copies are generated and the number of copies of the template is
increased exponentially.
MRSA (methicillin resistant Staphylococcus aureus) bacteria causes skin infections with the following signs and symptoms: cellulitis, abscesses, carbuncles, impetigo, styes, and boils. Normal skin tissue doesn't usually allow MRSA infection to develop. Individuals with depressed immune systems and people with cuts, abrasions, or chronic skin disease are more susceptible to MRSA infection.
Herpes simplex infections are common and when they appear around the mouth and lips, people often refer to them as "cold sores" and "fever blisters." Canker sores are different than cold sores. Air droplets can spread the virus, as can direct contact with the fluid from the blisters. Cold sore treatment include over-the-counter medication as well as prescription medications.
Genital herpes, a viral infection by the herpes simplex virus (HSV), is transmitted during sexual contact with the mucous-covered linings of the mouth, vagina, or the genital skin. A typical outbreak begins with an itching or tingling sensation followed by redness of the skin and blister formation. The blisters and ulcers that form when the blisters break are painful to the touch, and last from 7 days to 2 weeks. Though there is no cure for herpes, there are ways to treat outbreaks.
Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis bacteria. Symptoms include weakness, fever, weight loss, night sweats and in worse cases, chest pain, shortness of breath, and coughing up blood. A person with an active infection (a positive TB skin test, abnormal chest x-ray and TB bacteria in their sputum) requires treatment with izoniazid, rifampin, ethambutol and pyrazinaide.
Hepatitis C is an inflammation of the liver due to the hepatitis C virus (HCV), which is usually spread by
blood transfusion, hemodialysis, and needle sticks, especially with intravenous
drug abuse. Chronic hepatitis C may be treated with interferon, usually in combination with anti-virals.
Whooping cough (pertussis) is highly contagious respiratory infection that is caused by the bacteria Bordetella pertussis. There are an estimated 300,000 plus deaths annually from whooping cough (pertussis). Whopping cough commonly affects infants and young children, but can be prevented with immunization with the vaccine. First stage whooping cough symptoms are a runny nose, sneezing, low-grade fever, a mild cough with the cough gradually becoming more severe. After one to two weeks, the second stage of whooping cough begins.
Malaria is an infectious disease transmitted by the bite of an infected Anopheles mosquito. Symptoms of malaria include chills, pain, fever, and sweating. Though mild cases of malaria can be treated with oral medication, severe cases require intravenous drug treatment and fluids.
Leprosy (Hansen's disease) is a disfiguring disease caused by infection with Mycobacterium leprae bacteria. The disease is spread from person to person through nasal secretions or droplets. Symptoms and signs of leprosy include numbness, loss of temperature sensation, painless ulcers, eye damage, loss of digits, and facial disfigurement. Leprosy is treated with antibiotics and the dosage and length of time of administration depends upon which form of leprosy the patient has.
Salmonella bacteria are known to cause salmonellosis, typhoid fever, and paratyphoid fever in humans. Salmonella infection is usually caused by ingesting large amounts of the bacteria in contaminated food or water.
Rotavirus is the most common cause of severe diarrhea among infants and children throughout the world. Almost all children have become infected with rotavirus by their third birthday. Repeat infections with different viral strains are possible, and most children have several episodes of rotavirus infection in the first years of life. Children between the ages of six and 24 months are at greatest risk for developing severe disease from rotavirus infection. Rotavirus symptoms include: fever, vomiting, watery diarrhea, and abdominal pain. Rotavirus infection can be associated with severe dehydration in infants and children.
Bird flu (avian flu, avian influenza) infection in humans may result from contact with infected poultry. There is a vaccine to prevent human infection with the H5N1 strain of the avian flu virus.
Plague is an infectious disease caused by the Yersinia pestis bacteria, which is primarily found in rodents the fleas that feed off of them. The bacteria are passed to humans through flea or rodent bites. There are three forms of plague: bubonic, septicemic, and pneumonic. The symptoms and method of transmission vary with each form of plague. Plague can be treated with antibiotics.
Cholera is an infectious disease characterized by intense vomiting and profuse watery diarrhea and that rapidly lease to dehydration and often death. Cholera is caused by infection with the bacteria Vibrio cholerae, which may be transmitted via infected fecal matter, food, or water.
Fragile X syndrome is the most common inherited form of mental retardation. It's caused by a mutation on the X chromosome. People with Fragile X syndrome suffer from physical, social, emotional, speech, language, sensory, intelligence, and learning impairments. There is no definitive treatment for Fragile X, though there are ways to minimize the symptoms.
Genetic disease is a disorder or condition caused by abnormalities in a person's genome. Types of genetic inheritance include single inheritance (for example, cystic fibrosis, sickle cell anemia, Marfan syndrome, and hemochromatosis), multifactoral inheritance, chromosome abnormalities (for example, Turner syndrome, and Klinefelter syndrome), and mitochondrial inheritance (for example, epilepsy and dementia).
Ramsay Hunt syndrome is an infection of a facial nerve that causes a red painful rash with blisters and facial paralysis. The herpes zoster virus causes the infection. The infection is treated with antiviral agents, steroids, and pain medications.
Valley fever (coccidioidomycosis) is a disease caused by the inhalation of the Coccidioides immitis or C. posadasii fungus. Symptoms are flu-like and resolve over two to six weeks. Infection typically requires no treatment, though there are many antifungal drugs to treat valley fever.
Leishmaniasis is a disease caused by the bite of an infected sand fly. The most common types of leishmania infection are cutaneous and visceral leishmaniasis. Leishmaniasis is found mainly in the subtropics and tropics. Symptoms and signs of cutaneous leishmaniasis include skin sores with a raised edge and central crater, while those with visceral leishmaniasis usually have fever, weight loss, and an enlarged liver and spleen.
Rocky Mountain spotted fever (RMSF) is an infectious disease that's transmitted by the bite of a tick infected with the Rickettsia rickettsii bacterial organism. Initial symptoms of RMSF include fever, nausea, vomiting, muscle pain and severe headache. Later symptoms include rash, abdominal pain, joint pain, and diarrhea. Treatment usually involves a tetracycline antibiotic.
Schistosomiasis (snail fever), a disease caused by parasites, causes a variety of symptoms and signs, such as cough, rash and bloody diarrhea. Praziquantel is used in the treatment of schistosomiasis.
Mycobacterium marinum (M. marinum) is bacteria found in fresh and saltwater that can infect the skin through cuts or scrapes, causing granulomas to appear on the skin near the site of infection. This infection may be treated with a long course of oral antibiotics.
Meningococcemia is a bloodstream infection caused by Neisseria meningitides. Meningococcemia symptoms include fever, headache, fatigue, and body aches. Meningococcemia is treated with intravenous antibiotics. There is an effective and safe vaccine to protect against most serogroups of meningococcus that cause meningococcemia.
Typhus is a disease caused by Rickettsia bacteria. Symptoms and signs include fever, headache, nausea, vomiting, diarrhea, and rash. Antibiotics are recommended as the treatment for endemic and epidemic typhus infections.
Monkeypox is a viral disease that causes symptoms such as fever, sweating, and a rash with papules and pustules on the face and chest. PCR, ELISA, or Western blot tests are used to diagnose monkeypox. Treatment usually involves administering a smallpox vaccination, cidofovir, and possibly vaccinia immune globulin.
Enterovirulent Escherichia coli (E. coli) are strains of related bacteria that have a strong propensity to cause gastrointestinal tract infections. Examples of strains include: EHEC (enterohemorrhagic E. coli), ETEC (enterotoxigenic E. coli), EPEC (enteropathogenic E. coli), EIEC (enteroinvasive E. coli), EAEC (enteroadherent E. coli), and EAggEC (enteroaggregative E. coli). Symptoms may vary depending on the strain the individual contracts. Infection is spread generally through contaminated food or drink.
Severe acute respiratory syndrome (SARS) is a respiratory disease caused by the coronavirus SARS-CoV. Symptoms include fever and shortness of breath. Patients with SARS often require oxygen and severe cases require mechanical ventilation.
Tularemia (rabbit fever) is an infection caused by the Francisella tularensis bacteria. People can become infected with tularemia by coming into contact with infected animals or via a tick bite. Symptoms and signs include fever, headache and rash. Tularemia is treated with streptomycin or gentamicin.
Microsporidiosis is an infection caused by the microsporidia parasite. The disease is uncommon in people with normal immune systems. Symptoms in people with immune deficiency include diarrhea, malabsorption, gallbladder disease, cough, labored breathing, urinary tract infection, bowel perforation and keratoconjunctivitis. Microsporidiosis treatment depends on the site of infection and the species of microsporidia involved.
Bocavirus infection is usually only found in those with lower respiratory infections or diarrhea. Symptoms include cyanosis, cough, wheezing, runny nose, vomiting, and fever. There is no treatment that effectively targets the bocavirus strain.
Leishmaniasis is caused by a parasite that is spread to humans through the bite
of infected sand flies.
Leishmaniasis exists in many temperate and tropical
countries of the world. The disease is most common in India, Bangladesh, Nepal,
Sudan, Ethiopia, Afghanistan, Algeria, Iran, Saudi Arabia, Syria, Brazil,
Colombia, Peru, and Bolivia.
The most common type of leishmaniasis is cutaneous
leishmaniasis. This causes nodules or sores to form on the skin, including the
skin of the face. Affected people may have a single lesion or many lesions.
Sores heal slowly over months to years and leave scars.
Another type is called
visceral leishmaniasis. Parasites infect the tissues of key organs, especially
the liver, spleen, and bone marrow. Serious cases are usually fatal if not
treated.
Uncommonly, people who have had cutaneous leishmaniasis may get new
sores in the mucous membranes of the mout...
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