Pathogens are basically microorganisms that are capable of causing diseases in organisms they invade and make their host. Pathogens derive their name from two Greek terms - 'pathos' denoting disease and 'geinen' meaning to produce.
According to another view, the word 'pathogen' has its origin in the Greek expression 'birth of pain'. Majority of these microorganisms or pathogens are infectious, such as bacteria or viruses causing diseases.
In addition, pathogens also include harmful parasites, such as protozoans and fungi. However, not all microorganisms are harmful or cause disease and hence, they are not called pathogens.
Pathogens are capable of invading their hosts though a number of conduits or substratum.
However, the major conduits or means by which pathogens come in contact with their host or invade them include the following: air contact or breathing; water contact or intake or skin and animal contact/ bite or ingestion.
While there are different time frames for pathogen infection by these means, actually contamination of soil has the most extended as well as relentless probability of sheltering the harmful and disease-bearing microorganisms.
In fact, the human body possesses several protections against a number of the more familiar pathogens, such as Pneumocystis, in the form of human immune system as well as by means of a number of 'useful' bacteria present in the natural flora of the human body.
Nevertheless, when the immune system or the 'beneficial' bacteria is hurt in any manner, for instance owing to chemotherapy, antibiotics taken to eliminate other pathogens or human immunodeficiency virus (HIV), the disease bearing bacteria or pathogenic bacteria that had been staved off may breed and result in harm to the host.
It may be mentioned here that such instances are known as opportunistic infections.
There are three phases concerning the spread of pathogens or disease-bearing microbes - first, they run away from their host, second, they travel or transmit to the new target and finally, they invade and subsequently contaminate the new host.
Transmission or spread of pathogens takes place in a number of different manners, normally depending on the natural balance or ecology of the microorganism.
For instance the pathogens that infect the respiratory system are normally transmitted by air or, in other words, are airborne.
On the other hand, pathogens that infect the digestive system are usually found in water or food and the infection occurs when the victim consumes the contaminated water or food.
According to epidemiologists, the transmission or spread of pathogens may be categorized into two common types - direct and indirect. And within these two types of transmission there are a number of different methods.
Direct pathogen transmission takes place when a host infected by the disease-bearing microorganism passes on the ailment to another host.
Microorganisms that usually transmit directly from one host to another are said to be highly susceptible to the environmental conditions and are not able to remain outside the body of its host for a long enough period.
For instance, pathogens that result in sexually transmitted disease (STDs) are those that are spread directly from the infected person to another host by means of blood, saliva or semen.
Pathogens or harmful microorganisms that cause sexually transmitted disease include Tremonema palidum (causing syphilis), Neisseria gonorrhoea (causing gonorrhea) as well as the pathogen that is responsible for Acquired Immunodeficiency Syndrome (AIDS) and Human Immunodeficiency Virus (HIV).
In fact, the microorganism or virus called Ebola that is responsible for the deadly viral hemorrhagic fever is also transmitted by direct contact through the blood of the infected person.
When a mediator is needed to transmit a pathogen from one host to another, it is known as indirect transmission. In such cases, the pathogen first leaves its host and harbors in a medium for sometime before invading and infecting the new host.
The mediator or agent to facilitate an indirect transmission of pathogens may be a living organism or lifeless object. Inanimate agents that transmit pathogens are denoted as disease vehicles, including air, water and food.
Fomites are also considered to be inanimate agents as the pathogen often harbors on them before invading their new hosts. Some common instances of such inanimate objects or substances include clothes, toys, bedding and even surgical instruments.
On the other hand, the most common living organisms that help in transmission of pathogens include insects, fleas, mites and rodents. As inanimate transmitting agents are called disease vehicle, the living organisms or animate agents are known as vectors.
It may be noted here that normally the ailments that get transmitted through indirect contact, especially in hospitals, are particularly known as nosocomial infections.
A number of viruses and bacterial germs that infect the respiratory tract are so light that they can be lifted by the wind and transported elsewhere without any difficulty. Such air-borne pathogens are breathed in by susceptible victims later on resulting in lung infections.
In fact, a bacterial spore or germ of the anthrax variety is a common example of an air-borne pathogen called bacterium Bacillus anthraci.
This bacterium develops germs or spores (dormant non-reproductive body formed by certain bacteria in response to adverse environmental conditions) that are able to distribute by means of the air and when they are breathed in by humans they are capable of resulting in acute ailments of the respiratory tract.
In fact, even biological weapons of mass destruction can be prepared with anthrax spores with a view to contaminate hundreds and thousands of people when they are exploded.
It may be mentioned here that at the beginning of this millennium, in 2001, a bio-terrorist led to an outbreak of an epidemic in the United States who put bacterial spores in mail with a view to infect the people who handled the envelopes with anthrax when they inhaled the spores or germs came in contact with their skin.
Water is a very common agent to pass on or spread pathogens indirectly. When people consume water contaminated by these harmful microorganisms, they enter the victim's digestive system and invade and subsequently infect the alimentary canal.
What is worse is that a number of pathogens try to penetrate the cells coating the digestive tract and enter the bloodstream causing havoc to our health. When these harmful microorganisms succeed in entering the bloodstream, they can cause a systemic infection.
In other words, this may result in the contamination of the entire body. Vibrio cholera, a bacterium that results in cholera, is a very widespread water-borne pathogen.
Although this deadly disease has been brought under control in most regions of the world, water contaminated by this bacterium still causes cholera in some parts of the world where the hygienic conditions are below the desired standards.
Pathogens that are transmitted by means of foodstuff are categorized in two groups - the first group includes pathogens that generate contaminants that directly poison the host, while the second group comprises harmful microorganisms that contaminate the host and subsequently develop inside the victim's body.
You would be amazed to known that the bacterium Staphylococcus aureus is usually responsible for most of the food poisoning cases. When this particular bacterium contaminates the food it produces entero-toxins that cause vomiting and diarrhea in the victim.
Similarly, the bacterium Clostridium botulinum is the reason behind the ailment botulism - an extremely acute and, at times, fatal cases of food poisoning.
Animate agents transmitting pathogens or vectors offer an ideal shelter for the microorganisms and then transfer them to the humans either by biting them or by other means of contact.
Some animals are also very familiar vectors and they harbor the bacterium Coxiella burnetti that is responsible for Q fever.
This disease is transmitted to the humans when they deal with sheep. Insects are even common vectors or agents of transmitting pathogens and causing various diseases.
For instance, mosquitoes are responsible for transmitting the protozoan known as Plasmodium vivax that is responsible for causing malaria.
The spirochete Borrelia burgdorferi responsible for spreading Lyme disease is harbored by deer ticks (any of several ticks of the genus Ixodes that are parasitic on deer). On the other hand, rat flea transmits the bacterium that results in plague Yersina pestis.
The United States Centers for Disease Control has prepared a list of the pathogens that are most expected to be utilized as biological weapons and stated that the biological weapons are able to spread these pathogens by several different methods.
The list of pathogens prepared by this organization include air-borne virus Variola that is responsible for smallpox and air-borne bacterium bacillus anthracis.
In addition, the US Centers for Disease Control has warned that food-borne bacterium Clostridium botulinum, the Ebola virus transmitted directly by blood contact and Yersina pestis that needs a vector for transmission are also very likely to be used in biological weapons.
Pathogens transmitted by blood denotes disease-bearing microorganisms like bacteria and viruses that are present in the blood and may result in diseases to other individuals when they come in contact with such infected blood.
In addition to blood, these harmful microorganisms or pathogens are capable of passing on from one individual to another when the victims come in contact with any body fluid of the person already infected.
In fact, there are several diverse types of pathogens that can be transmitted by blood or body fluid contact.
The most precarious or harmful types of blood-borne pathogens include the Human Immunodeficiency Virus (HIV), Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV).
The human immunodeficiency virus (HIV) actually attacks our immune system gradually rendering incapable of functioning.
And, when the immune system weakens, our body becomes vulnerable to other lethal ailments. In due course, HIV results in the development of acquire immune deficiency syndrome that it a fatal disease still with no cure in sight.
This is despite the fact that even though the medical science as well as the treatment of AIDS have progressed several steps during the past few years, scientists are yet to invent any medication or therapy to cure this fatal disease transmitted by blood.
However, it may be noted here that it may take several years for the HIV to develop AIDS and all these years and after an individual has developed AIDS are extremely agonizing indeed.
Similar to any other pathogens transmitted by blood, the human immunodeficiency virus (HIV) too is able to enter the human body through abrasions, unprotected sexual contact, open wounds, blisters, and even the mucous membranes of the mouth, nose and eyes.
Hence, it is particularly imperative for people in the health industry as well as the emergency responders to adopt additional precautions and protective measures while handling any type of infected blood.
While the human immunodeficiency virus (HIV) attacks our immune system rendering it weak to carry out its normal functions of protecting the body from alien attacks, the hepatitis B virus contaminates as well as results in the inflammation of the liver.
Like HIV, hepatitis B virus (HBV) too is transmitted by blood, precisely speaking, direct blood-to-blood contacts, and may result in acute conditions like cancer of the liver and cirrhosis.
Although there is no absolute cure for hepatitis B yet, a vaccine was developed in 1982 - considered to be a major breakthrough in treating hepatitis B patients.
Ever since several patients have been inoculated with this vaccine and it has proved to be effectual in saving quite a number of lives.
In addition, the vaccine is also reported to have brought down the number of hepatitis B cases among people, especially children and adolescents.
In fact, the complete dosage of the vaccine comprises three injections given at intervals and works by gradually fortifying the immune system against the invasion of hepatitis B virus.
Majority of the adults assailed by the hepatitis B virus will recover completely provided the patients always remember to adopt adequate precautions with a view to thwart the transmission of the deadly virus.
Among all the hepatitis viruses identified so far, the hepatitis C virus (HCV) is considered to be the deadliest. The hepatitis C virus is the primary reason behind severe and chronic liver ailments that may eventually develop into cancer as well as cirrhosis of the liver.
In fact, majority of the people infected by hepatitis C virus (HCV) are usually not aware that they are suffering from the deadly disease till they experience initial symptoms of liver damage.
Incidentally, the symptoms of liver damage may appear several years after an individual has actually been infected by the virus.
Normally, the most common way that an individual may contract this deadly virus is by coming in contact with infected blood by sharing needles already used to injected persons contaminated by the virus or when the injection needles are shared by illegal drug users.
In fact, if there are only minor abnormalities owing to infection by hepatitis C virus, the patient may not require any treatment.
The physician will be able to monitor the condition of the liver only by means of follow-up blood examinations. Alternately, the doctors may also prescribe anti-viral medications to treat such patients.
However, if the patient's condition turns acute owing to a severe liver damage, the patient may need liver transplant. Even after the liver transplant, a patient will be required to take anti-viral medicines, as hepatitis C (HCV) is not curable by such liver transplants.
While quite a number of bacteria are transmitted by food, the most common food-borne bacteria identified by scientists thus far include Salmonella, Campylobacter and E. coli O157:H7 as well as a collection of viruses known as calicivirus - also called Norwalk and bacteria similar to Norwalk.
This bacterium is commonly found in the intestines of mammals, reptiles and birds and has the aptitude to transmit to humans by means of a range of foods that are of animal origin, such as meat, poultry etc.
The illness caused by this bacterium is known as salmonellosis with common symptoms like fever, abdominal spasms and/ or diarrhea.
People with poor fundamental health or failing immune systems are more vulnerable to attacks by this bacterium and they face the risk of fatal infections if the virus succeeds in penetrating their bloodstream.
Infection by these bacteria is considered the most common cause for all types of diarrhea across the globe. People infected by this bacterial pathogen experience symptoms like diarrhea, fever and abdominal spasms.
These bacteria are commonly found in the intestines of birds and are present in majority of poultry meat.
Consumption of inadequately cooked chicken or other food that has been infected with fluids trickling from uncooked chicken is said to be the most common cause of infection by Campylobacter.
This bacterial pathogen is found in abundance in cattle as well as other comparable animals. Usually, people develop E. coli when they consume food or water that has been infected even with the minutest amount of cow excrement.
This bacterium usually causes a deadly ailment with symptoms of acute and bloody diarrhea as well as excruciating abdominal spasms. However, the patients do not experience much fever when infected by E. coli O157:H7 virus.
Around three to five per cent of the patients enduring E. coli develop a problem known as hemolytic uremic syndrome (HUS) that may take place even more than a few weeks of contacting the virus.
This acute complication is accompanied by profuse bleeding (hemorrhage), kidney failure as well as a short-term anemia owing to hemorrhage.
Most illnesses transmitted by virus by means of food are caused by Calicivirus or Norwalk-like virus. However, the diseases caused by this virus are seldom diagnosed owing to inadequacy of laboratory tests at all places.
Infection by this virus results in gastrointestinal ailments - normally with more vomiting than diarrhea.
However, these problems subside and gradually disappear within two days of occurrence. While most food-borne viral pathogens are usually found in abundance in animals, Calicivirus or Norwalk-like virus is generally believed to transmit from one diseased individual to another.
This virus is so easily transmitted that if kitchen workers are infected by this virus, they may contaminate while preparing a sandwich or salad without wearing gloves.
It has been seen that on many occasions fishermen infected with this virus contaminate oysters while they harvest them.
Some of the ailments are sporadically transmitted by means of foods consumed by people. However, these diseases may also be spread by a number of other different ways.
Pathogens that are transmitted in thus manner include hepatitis A, Shigella as well as parasites called Cryptosporidia and Giardia lamblia.
In addition to these harmful microorganisms, at times, ailments like strep throat (a severe sore throat caused by hemolytic streptococci with symptoms of fever and prostration) is also transmitted by means of foods consumed.
Besides the ailments attributable to express contamination, a number of food-borne ailments also develop owing to the existence of toxins produced by a germ in the food consumed.
For instance, the bacterium Staphylococcus aureus has the ability to develop in some types of foods and produce a contaminant or venom that results in acute vomiting.
Similarly, when the bacterium Clostridium botulinum develops and brings into being potent paralytic venom in foods, it results in an uncommon, but lethal malady called botulism.
All these toxins or contaminants have the aptitude to cause diseases even after the germs causing them no longer exist in the foods.
In addition to the pathogens discussed above, there are other contaminates and venomous compounds that may result in diseases caused by harmful microorganisms transmitted by means of foods consumed.
In fact, people may fall sick if any pesticide is unintentionally combined or put into a food or any one makes use of any poisonous substance occurring in the nature in food preparation.
It may be mentioned here that every year people fall sick after eating toxic mushrooms considering them to be safe for consumption. Similarly, consumption of poisonous reef fishes also results in many people to becoming ill every year.
Pathogens transmitted by air are quite different from those transmitted by blood or food. While the blood pathogens spread by coming in direct contact with blood, the food-borne pathogens invade the humans when foods or water infected by the microbes are consumed by people.
On the contrary, pathogens transmitted by the air invade an individual when he or she inhales the air carrying the microbes. And in such cases, the respiratory system is the first to be affected.
Basically, there are three varieties of pathogens that are transmitted by air - bacterial, fungal and viral.
When a person who is already infected by any of these pathogens sneezes or coughs, they send out minute drips of moisture into the air and such droplets of moisture contains the pathogens.
The environment plays an important role vis-à-vis the period of time these pathogens can remain air-borne. An arid atmosphere not only enables these contaminants to remain airborne for several hours, but also help them to travel greater distances.
On the other hand, if there is too much humidity, the pathogens are unable to remain in the air for longer time or travel longer distances. When any individual inhales an air-borne pathogen, it is said to be transmitted.
However, it needs to be mentioned that being exposed to air-borne pathogens does not necessarily mean that the individual will be infected by the microbes.
Below is a brief discussion regarding some of the air-borne pathogens that are not only common, but keeps us worried all through the day.
A particular type of bacteria is responsible for causing the pulmonary disease tuberculosis, called TB in short. Usually, these bacteria assail the lungs, but in specific cases it has the ability to even affect the brain, kidneys and spine.
Tuberculosis is a worldwide concern as it affects several million people every year and as many as three million patients succumb to this disease annually.
What is worse is that experts forecast that by the year 2050 this disease would be claiming five million lives each year.
It has been seen that a number of people who have been infected by tuberculosis may not feel sick as their immune system is continually combating the bacteria, which is not considered to be infectious.
However, approximately 10 per cent of the people infected by the tuberculosis bacteria may eventually develop the disease at a later stage and then the bacteria are certain to become contagious.
The most common way by which an individual may be infected by the tuberculosis (TB) bacteria is when he or she inhales the contaminated air exhaled by a person who is already infected by the bacteria through sneezing or coughing.
The tuberculosis pathogens are able to survive for a maximum period of one to one-and-a-half hours outside the body depending on the size of a room, ventilation of the room as well as several other aspects.
In the United States alone, the rate of death among patients hospitalized for treatment of acute tuberculosis is about four per cent.
People around the world were overtaken by a fresh panic when a new disease called severe acute respiratory syndrome (SARS) broke out in many parts of the globe in 2003. In fact, SARS is basically a contagious disease that is attributed to the SARS coronavirus.
This air-borne virus is spread when any person infected by the pathogen sneezes or coughs when they are in close proximity with other normal people.
During that year, as many as 8,096 people were infected by the virus and among these around 10 per cent of the patients succumbed to SARS across the world.
However, only seven people in the United States are known to have contacted this viral disease at that time. Interestingly enough, all of them were infected by the virus when they were traveling abroad to places where the disease had spread like an epidemic.
Bird flu or avian influenza is a contagion attributed to the avian or bird influenza viruses. Such influenza viruses are present naturally in the body of almost all birds.
Although the wild birds bear the viruses in their intestines and fly across the globe with them, more often than not they themselves do not fall sick owing to the pathogens.
Nevertheless, avian influenza is very infectious and may contaminate several domesticated birds, such as ducks, chickens and turkeys making them severely ill and eventually killing them.
Scientists are actually concerned over the fact that some day the avian influenza of H5N1 type may infect humans as all the influenza viruses have the aptitude to transform.
They fear that once H5N1 is able to infect the humans, it would easily transmit from one human to another giving rise to an epidemic.
It is important to note that as these viruses have not infected the humans so far, the immune system in the humans do not have any mechanism to protect them against avian influenza or bird flu.
Hence, there is little doubt that when the avian influenza viruses will succeed in infecting humans, they will cause havoc by spreading an influenza pandemic worldwide.
In such a situation, the disease will easily transmit from one person to another affecting millions. And the worst thing is that while the human immune system is not prepared to combat these viruses, there is still no cure for the deadly infectious disease.
Methicillin-resistant Staphylococcus aureus (MRSA) is basically a spherical bacterium often found living on the skin or in the nose of an individual.
This bacterium may cause a variety of ailments ranging from minor conditions, such as skin infections like boils, pimples, abscesses (localized gathering of pusses in any part of the body) and cellulitis (inflammation of cellular tissue) to acute and fatal disease, including meningitis, pneumonia, endocarditis (inflammation of the endocardium), toxic shock syndrome (TSS) and even septicemia (blood poisoning).
Basically, the bacterium causes infection in the upper region of the respiratory tract and in medical facilities; it is the most widespread reason for Staph contagions.
In fact, Methicillin-resistant Staphylococcus aureus (MRSA) are detached parts of the bacterium that have obtained genes capable of programming resistance of antibiotics to all types of penicillins, inclusive of methicillin and additional contracted range of ß-lactamase-resistant penicillin antibiotics.
This type of bacterium is presently extensively prevalent in the neighborhood hospital surroundings and hence, MRSA has been commonly nick-named as a 'superbug'.
It is surprising to note that this bacterium has been conventionally considered to be an infection that is associated with hospitals.
Infection by this superbug is not only difficult to cure, but MRSA is also known to be resistant to most medications. Nevertheless, it has been found that gaseous ozone is highly effectual in reducing the presence of this bacterium.
Stachybotrys is a fungus responsible for causing a disease called mycotoxicosis in humans as well as animals. This virus is also known as 'black mold' and it produces a venomous substance called mycotoxin, which is the main cause for the disease.
During the last 15 years, scientists have collected substantiation across North America that shows that Stachybotrys is an acute predicament in most homes and buildings.
In addition, this fungus is also responsible for developing a malady called 'sick building syndrome'. This ailment may often turn out to be deadly.
So fact, scientists have been able to identify around 15 diverse species of this fungus that develop and thrive well in relatively damp places when the humidity is usually over 50 per cent.
Cladosporium, Penicillium, Aspergillus and Alternaria are the most familiar molds (growths of minute fungi forming on vegetable or animal matter) found inside any building.
When these molds are restrained, especially Penicillium is helpful in producing different varieties of cheese as well as the antibiotic called penicillin.
However, at times these fungi also result in contaminating humans and the disease owing to such fungal infections is called penicilliosis.
In fact, scientists and medical practitioners have so far been able to isolate Penicillium from patients suffering from endophtalmitis (inflammation of the ocular cavities), keratitis (inflammation of the cornea), necrotizing esophagitis (black esophagus owing to fungal infection), otomycosis (fungal infection of the external auditory canal), peritonitis (inflammation of the peritoneum), endocarditis (inflammation of the endocardium), pneumonia and even in the infections of the urinary tract.
It has been seen that the majority of Penicillium contagions occur in people whose immune systems are stifled. In other words, this type of fungi is usually found in immune-suppressed hosts.
It may be mentioned here that young people who are exposed to persistent Penicillium mould infection are known to have developed an immune reaction that is denoted as perils of cardiac failure.
