Humans may be just another opportunity for housing.
The tenancy of some species can cause diseases.
Humans and their ancestors have been affected by plagues and diseases for millions of years.
In the past several centuries, people have understood that staying away from sick people, disposing of corpses and personal belongings of victims of illness, and using sanitary practices reduced their own chances of getting sick.
Epidemiologists study how diseases are transmitted.
A disease that occurs in a high number of people at the same time.
There were records about infectious diseases as far back as 3000 B.C.
Several hundred years have passed since a number of significant pandemics were caused bybacteria.
The decline of cities and nations was caused by some of the most memorable pandemics.
In the 21st century, infectious diseases remain the leading cause of death despite advances in medical research and treatments.
The pathogen that causes the disease is passed from one person to another.
To cause disease, a pathogen must be able to reproduce in the host's body and cause damage.
The Plague of Athens killed one-quarter of the Athenian troops who were fighting in the great Peloponnesian War and weakened Athens's dominance and power.
People living in overcrowded Athens as well as troops aboard ships that had to return to Athens were affected by the plague.
The source of the plague may have been identified recently when researchers from the University of Athens were able to use DNA from teeth recovered from a mass grave.
The scientists were able to identify the sequence of genes from the disease, which causes typhoid fever.
Typhoid fever is caused by a Gram-negative, rod-shaped proteobacterium.
Typhoid fever is spread through feces and can cause a wide range of symptoms.
Between 16 and 33 million cases of this re-emerging disease occur annually, resulting in over 200,000 deaths.
There are carriers of the disease.
In the early 1900s, a cook named Mary Mallon spreadphoid Mary to over fifty people and three of them died.
One-quarter to one-half of the human population in the eastern Mediterranean region were wiped out by the Plague of Justinian.
Europe's population dropped by 50 percent during this outbreak.
The plague is caused by a bacterium.
It is thought to have originated in China and spread along the Silk Road, a network of land and sea trade routes, to the Mediterranean region and Europe.
One of the symptoms of the Black Death is tissue necrosis.
The bubonic plague caused swollen areas of the lymphatic tissue.
A pneumonic form of the plague can cause death within a week if it is spread by coughing and sneezing.
The rapid spread of the Black Death in Europe was caused by the pneumonic form.
The world's population was reduced from 450 million to about 350 million by the Black Death.
The plague hit London again in the 1600s.
A "sylvatic" form of plague, carried by fleas on rodents such as prairie dogs and black footed ferrets, can cause up to 20 cases of plague annually in the American Southwest.
The mortality rates from plague are low because the bacterium responds to several types of modern antibiotics.
20 percent of the city's population was killed by the Great Plague of London.
The (b) bacterium is a Gram-negative, rod-shaped bacterium.
The disease can be spread through the bite of a flea.
There are many symptoms, including a swollen lyspian, a seizure, vomiting of blood, and gangrene.
The accidental "biological warfare" that resulted from the transport of a pathogen into a population that had not previously been exposed to it was one of the negative consequences of human exploration.
When European conquerors reached the western hemisphere, they brought with them disease-causingbacteria and viruses, which devastated many Native Americans, who had no natural resistance to many European diseases.
Up to 90 percent of Native Americans died from infectious diseases after Europeans arrived, making conquest of the New World a foregone conclusion.
The distribution of a disease can change.
The spread of a disease can be impacted by changes in the environment.
Re-emerging diseases were previously under control.
Most of the infectious diseases affecting humans are zoonotic.
Brucellosis is an example of a prokaryotic zoonosis that is re-emerging in some regions, and necrotizing fasciitis has been increasing in virulence for the last 80 years.
There are emerging diseases.
There are regions on the map where diseases are emerging or re-emerging.
Some of the emerging diseases are not new, but are diseases that devastated populations and became dormant for a while, just to come back and be more deadly than before.
Tuberculosis was under control in some regions of the world until it came back, mostly in urban centers with high concentrations of immunocompromised people.
The WHO has identified diseases that should be monitored.
There are three viral diseases, threebacterial diseases, and a bubonic plague.
There is no end to the war against infectious diseases.
The disease is caused by a Gram-negative bacterium.
The ticks may feed on humans, but deer are the preferred host.
Chronic disorders in the nervous system, eyes, joints, and heart are caused by the disease.
The disease is named after Connecticut, where an outbreak occurred in 1995 and has since spread.
The disease is not new.
Otzi the Iceman, a 5,300-year-old mummy found in the Alps, may have been exposed to Borrelia.
Food is not an exception as prokaryotes colonize the surface of any type of material.
Most of the time, prokaryotes colonize food and food-processing equipment in the form of a biofilm.
Infections related to food consumption are common.
A food poisoning is an illness caused by the consumption of food that has been contaminated.
Over time, the characteristics of foodborne illnesses have changed.
Clostridium botulinum is a bacterium that can cause botulism, a potentially fatal disease.
Non-acidic canned foods, homemade pickles, and processed meat and sausages were some of the most common sources of this bacterium.
Clostridium could grow in the can, jar, or package.
The incidence of this disease has been reduced by proper canning procedures.
People tend to think of food-borne illnesses as associated with animals, but most cases are linked to produce.
In the United States and Germany, there have been serious produce-related outbreaks associated with raw spinach, and these have become more common.
The outbreak of E. coli in 2006 was caused by the bacterium O157:H7.
There are many different types ofbacteria that carry a set of similar antigens on their cell surface.
O157:H7 is a potentially fatal strain of E. coli and is not particularly dangerous to humans.
All types of food can be contaminated.
The recent outbreak ofSalmonella occurred in foods as diverse as peanut butter and eggs.
A deadly outbreak in Germany in 2010 was caused by E. coli.
It was found that the strain that caused the outbreak was a new type of E coli.
There are more cases of listeriosis due to contaminated meat, cheese, and vegetables.
Shiga toxin is produced by the E. coli O104:H4 strain.
The red blood cells are destroyed by the toxin.
Affected by the 2011 outbreak were 845 patients, who had red blood cells that were not functioning.
Some patients experience problems with their kidneys years later.
It is very difficult to destroy biofilms.
They are responsible for diseases such as Legionnaires' disease and otitis media.
They produce dental plaque and colonize catheters.
They form in wounds and burned tissue.
In healthcare environments, biofilms grow on machines.
In the hospital, 65 percent of infections are attributed to biofilms.
Food-processing equipment that isn't adequately cleaned and biofilms that colonize the surfaces of vegetable leaves and meat are related to diseases contracted from food.
The film may not cause immediate symptoms.
Host defense mechanisms are rarely used to resolve them.
It is very difficult to eradicate infections caused by a biofilm because they tend to be resistant to most antibiotics.
The matrix that protects the cells from antibiotics or drugs is attached to another matrix.
Since biofilms grow slowly, they are less responsive to agents that interfere with cell growth.
It has been reported that biofilms can resist up to 1,000 times the antibiotic concentrations used to kill the samebacteria when they are free-living or planktonic.
Scientists are working on new ways to get rid of biofilms because an antibiotic dose that large would harm the patient.
The healthcare community is challenged by all these questions.
Overexposure to antibiotics is one of the main causes of antibiotic resistance.
The imprudent and excessive use of antibiotics resulted in the natural selection of resistant forms ofbacteria.
Most of the infectingbacteria are killed by the antibiotic.
There is an increase in the proportion of resistant forms over non-resistant ones.
Transferring resistance genes from one cell to another is one of the ways that resistance genes can be spread.
The misuse of antibiotics in patients with colds or the flu is a big problem.
The excessive use of antibiotics in livestock is a problem.
The use of antibiotics in animal feed promotes resistance to them.
70 percent of the antibiotics produced in the US are fed to animals.
These antibiotics are given to livestock in low amounts, so that they are less likely to develop resistance and thus less likely to be passed on to humans.
There is a news report on the problem of routine antibiotic administration to livestock.
The use of antibiotics has led to the expansion of resistant populations.
Staph is a common bacterium that can live in the human body and can be easily treated with antibiotics.
This strain is resistant to many antibiotics.
MRSA can cause infections of the skin, but it can also cause infections of the bloodstream, lungs, urinary tract, or sites of injury.
While MRSA infections are common among people in healthcare facilities, they have also appeared in healthy people who haven't been hospitalized, but who live or work in tight populations.
Researchers are concerned about the way this source of MRSA targets a younger population than those living in care facilities.
The scanning electron micrograph shows MRSA.
Food poisoning and skin and respiratory infections can be caused by S. aureus.
The medical community is facing an antibiotic crisis.
After years of being protected from infections by antibiotics, some scientists think we may be going back to a time when a simple bug could kill the population.
It takes many years of research and clinical trials and millions of dollars to create an effective and approved drug.
Epidemiology studies the occurrence, distribution, and determinants of health and disease in a population.
It is part of public health.
Epidemiologists track the spread of a disease to identify the original mode of transmission.
They work with historians to try to understand the evolution of a disease and the natural history of pathogens.
They gather information from a variety of sources.
Public health policies can be designed to reduce the incidence of a disease or to prevent its spread.
Epidemiologists conduct rapid investigations in case of an outbreak to recommend measures to control it.
An epidemiologist has a bachelor's degree and a master's degree.