Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.
Infection with Y. pestis causes plague in humans. Y.
pestis is a bacterium that is gram-negative rod-shaped bacterium genetically
related to Escherichia coli that resembles a "safety pin" when stained with
chemicals and viewed with a microscope. In general, plague circulates in rodent
populations where infected fleas on rodents transfer the bacteria to other
rodents. When the rodent population invades human habitats or when humans invade
rodent habitats, the infected fleas on the rodents will also bite humans. This
flea bite begins plague in an individual. However, once a human is infected, it
is fairly easy for that person to infect other people with the organisms
especially if they develop pulmonary infection because droplets containing Y.
pestis from the lungs are expelled into the air and can infect other humans.
Figure 1: Picture of Yersinia pestis, showing bipolar staining or "safety pin" appearance. SOURCE: CDC/Courtesy of Larry Stauffer, Oregon State
Public Health Laboratory
How is plague spread?
Plague is a zoonotic (animal to animal) disease that can be spread to humans
by several methods. The usual way humans encounter plague is from getting a flea
bite from a flea that has previously been infected from biting an animal where
the disease is endemic. Most often this is attributed to a plague-infected rat
population, but it could be from many other animals such as mice, prairie dogs,
squirrels, and other rodents. Unfortunately, even domestic cats and dogs can
become infected and potentially may transmit the disease to humans. Dead animals
can still contain many viable Y. pestis; humans can become infected when they
handle these animals; people should use caution when touching touch dead animals
or even getting close to them as they may have fleas looking for another warm
(human) body to bite. Human-to-human spread is easily done by people with
pneumonic plague as they can spread infected droplets expelled from the lungs to
other people or to objects that are subsequently touched by others. Individuals
with bubonic or septicemic plague can also transmit the disease, usually by
direct or indirect contact with infected body fluids or objects that come in
contact with these fluids. Spread of plague can be facilitated when conditions
arise that encourage rat populations to rapidly increase. For example, when
cities reduce or fail trash pickup for any extended time period, a rat
population may flourish, and so may the flea population. Consequently, human
behaviors (warfare, economic failures, urban expansion, and others) may augment
the development of plague.
Abdominal pain is pain in the belly and can be acute or chronic. Causes include inflammation, distention of an organ, and loss of the blood supply to an organ. Abdominal pain can reflect a major problem with one of the organs in the abdomen such as the appendix, gallbladder, large and small intestine, pancreas, liver, colon, duodenum, and spleen.
Low blood pressure, also referred to as hypotension, is blood pressure that is so low that it causes symptoms or signs due to the low flow of blood through the arteries and veins. Some of the symptoms of low blood pressure include light-headedness, dizziness, or even fainting if not enough blood is getting to the brain. Diseases and medications can also cause low blood pressure. When the flow of blood is too low to deliver enough oxygen and nutrients to vital organs such as the brain, heart, and kidneys; the organs do not function normally and may be permanently damaged.
Pneumonia is inflammation of one or both lungs with consolidation. Pneumonia is frequently but not always due to infection. The infection may be bacterial, viral, fungal or parasitic. Symptoms may include fever, chills, cough with sputum production, chest pain, and shortness of breath.
Headaches can be divided into two categories: primary headaches and secondary headaches. Migraine headaches, tension headaches, and cluster headaches are considered primary headaches. Secondary headaches are caused by disease. Headache symptoms vary with the headache type. Over-the-counter pain relievers provide short-term relief for most headaches.
Lymph nodes help the body's immune system fight infections. Causes of swollen lymph nodes (glands) may include infection (viral, bacterial, fungal, parasites). Symptoms of swollen lymph nodes vary greatly. They can sometimes be tender, painful or disfiguring. The treatment of swollen lymph nodes depends upon the cause.
Chronic cough is a cough that does not go away and is generally a symptom of another disorder such as asthma, allergic rhinitis, sinus infection, cigarette smoking, GERD, postnasal drip, bronchitis, pneumonia, medications, and less frequently tumors or other lung disease. Treatment of chronic cough is dependant upon the cause.
Although a fever technically is any body temperature above the normal of 98.6 degrees F. (37 degrees C.), in practice a person is usually not considered to have a significant fever until the temperature is above 100.4 degrees F (38 degrees C.). Fever is part of the body's own disease-fighting arsenal: rising body temperatures apparently are capable of killing off many disease- producing organisms.
Chest pain is a common complaint by a patient in the ER. Causes of chest pain include broken or bruised ribs, pleurisy, pneumothorax, shingles, pneumonia, pulmonary embolism, angina, heart attack, costochondritis, pericarditis, aorta or aortic dissection, and reflux esophagitis. Diagnosis and treatment of chest pain depends upon the cause and clinical presentation of the patient's chest pain.
Influenza (flu) is a respiratory illness caused by a virus. Flu symptoms include fever, cough, sore throat, runny nose, headache, fatigue, and muscle aches. The flu may be prevented with an annual influenza vaccination.
Medical shock is a life-threatening medical condition. There are several types of medical shock, septic shock, anaphylactic shock, cardiogenic shock, hypovolemic shock, and neurogenic shock. Causes of shock include heart attack, heart failure, heavy bleeding (internal and external), infection, anaphylaxis, spinal cord injury, severe burns, chronic vomiting or diarrhea. Low blood pressure is the key sign of sock. Treatment is dependant upon the type of shock.
Drug resistance (antimicrobial resistance) is the ability of bacteria, fungi, parasites, and viruses to grow, even in the presence of a drug that would normally kill it (or limit it's growth). Drug resistance is a growing problem, particularly for infections such as MRSA, VRE (vancomycin-resistant enterococci), tuberculosis, HIV, STDs, gonorrhea, flu, pneumonia, malaria, E. coli, salmonella, Campylobacter, which causes diarrhea and gastroenteritis. Learn how to protect yourself from resistance to drugs.
Bioterrorism is a form of terrorism where there is the intentional release of biological agents such as viruses, germs, or bacteria. Diseases caused by bioterrorism agents include anthrax, botulism, plague, smallpox, tularemia, brucellosis, food poisoning, Q fever, ricin toxin poisoning, cholera, epidemic typhus, viral encephalitis, XDR TB, and MDR TB.
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