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Thursday, January 19, 2012

Signs and Symptoms of Herpes simplex virus infection


HSV-1

  • Small, painful blisters filled with fluid around the lips or edge of the mouth
  • Tingling or burning around the mouth or nose (often a few days before blisters appear)
  • Fever
  • Sore throat
  • Swollen lymph nodes in neck

HSV-2

  • Tingling sensation in the genitalia, buttocks, and thighs
  • Small red blisters or open sores on genitals or inner thighs; in women, often occur inside the vagina
  • May be painful or not
  • In women, vaginal discharge
  • Fever, muscle aches
  • Headache
  • Painful urination
  • Swollen lymph glands in the groin
References: http://www.umm.edu/altmed/articles/herpes-simplex-000079.htm


Monday, December 26, 2011

Herpes simplex virus


Herpes simplex virus (HSV) infections are very common worldwide. HSV-1 is the main cause of herpes infections that occur on the mouth and lips, including cold sores and fever blisters. It is transmitted through kissing or sharing drinking utensils. HSV-1 can also cause genital herpes, however, HSV-2 is the main cause of genital herpes. HSV-2 is contracted through sexual contact. You may be infected with HSV-1 or HSV-2 but not show any symptoms. Often symptoms are triggered by exposure to the sun, fever, menstruation, emotional stress, a weakened immune system, or an illness.

There is no cure for herpes, and once you have it, it is likely to recur; however, some people may have one outbreak and then never have another one. In between herpes outbreaks, the virus lies dormant (as if it is hibernating or sleeping) in nerve cells.

While exposure to HSV-1 is extremely common – as many as 90% of American adults have been exposed to the virus – and there is no stigma to having a cold sore, HSV-2 or genital herpes can cause embarrassment. Although there is no cure for genital herpes, an infected person can take steps to preventing spreading the disease and can continue to have a normal sex life.

While most herpes infections do not cause serious complications, infections in infants and in people with weakened immune systems or herpes infections that affect the eyes can be life threatening.


Monday, December 5, 2011

How can plague be prevented?

1. People who live, work, or play in areas with active plague infection in wild rodents should take these precautions:

  • Eliminate food and shelter for rodents around homes, work places, and certain recreation areas, such as picnic sites or campgrounds where people congregate. Remove brush, rock piles, junk, and food sources, including pet food.
  • Allow health authorities to use appropriate and licensed insecticides to kill fleas during plague outbreaks in wild animals.
  • Treat pets (cats and dogs) for flea control regularly.
  • Avoid sick or dead animals, and report such animals to the health department. Hunters and trappers should wear rubber gloves when skinning animals.
  • Use insect repellents when outdoors in areas where there is a risk of flea exposure.

2. Preventive treatment with antibiotics is recommended for: 1) people who are bitten by fleas during a local outbreak or who are exposed to tissues or fluids from a plague-infected animal; 2) people living in a household with a bubonic plague patient, since they may also be exposed to infected fleas; and 3) people in close contact with a person or pet with suspected plague pneumonia. Close contacts defined as face-to-face contact or being in the same closed space, such as a room or vehicle.

3. People who travel to countries where plague occurs should take these additional precautions:

  • Avoid exposure to fleas from diseased rats. The risk of being bitten by infected fleas is especially high after large numbers of plague-infected rats have died. Therefore, avoid places that are infested with rats or where large numbers of rats have reportedly died.
  • If travel to such areas is essential, apply insect repellent containing DEET to legs and ankles. Also apply repellents and insecticides to clothes and outer bedding according to manufacturers' instructions.
  • Take preventive antibiotics if the risk of exposure is high.

Ref:
http://www.dhpe.org/infect/plague.html

Wednesday, November 30, 2011

Who is at risk for plague?

  • People who live in rural areas where plague occurs in wild rodents
  • People, such as biologists, trappers, and hunters, who handle potentially infected animals
  • Campers, hikers, travelers, and others in areas where plague is known to exist
  • People in close contact with pneumonic plague patients

Thursday, November 24, 2011

What is the treatment for plague?

If diagnosed in time, plague is treatable with antibiotics. Treatment of suspected plague cases should start as soon as possible after the laboratory specimens are taken. The drug of choice is streptomycin, but several other antibiotics are also effective.

Sunday, November 6, 2011

How is plague diagnosed?


U.S. health-care providers should suspect plague in anyone with large, painful, very tender lymph gland accompanied by fever, extreme tiredness, and a history of exposure to possibly infected rodents and their fleas in the western United States. Plague should also be suspected in a person with plague symptoms plus a history of handling sick or dead cats, or wild animals such as rabbits.

Patients with suspected plague should be hospitalized, placed in isolation, have specimens obtained for plague diagnosis, and immediately treated. All suspected plague cases must also be reported to local and state health departments.

Ref: http://www.dhpe.org/infect/plague.html

Sunday, October 30, 2011

How soon after exposure do symptoms appear?



Symptoms usually begin within 2 to 6 days after exposure to the plague bacteria.

Saturday, October 22, 2011

What are the signs and symptoms of plague?


When a person is bitten by an infected flea or is infected by handling an infected animal, the plague bacteria move through the bloodstream to the lymph nodes. The lymph nodes swell, causing the painful lumps ("buboes") that are characteristic of bubonic plague. Other symptoms are fever, headache, chills, and extreme tiredness. Some people have gastrointestinal symptoms.

If bubonic plague goes untreated, the bacteria can multiply in the bloodstream and produce plague septicemia (septicemia plague), severe blood infection. Signs and symptoms are fever, chills, tiredness, abdominal pain, shock, and bleeding into the skin another organs. Untreated septicemia plague is usually fatal.

Pneumonic plague, or plague pneumonia, develops when the bacteria infect the lungs. People with plague pneumonia have high fever, chills, difficulty breathing, a cough, and bloody sputum. Plague pneumonia is considered a public health emergency because a cough can quickly spread the disease to others. Untreated pneumonic plague is usually fatal.

Tuesday, October 11, 2011

How do people get plague?


  • By the bites of infected fleas
  • By direct contact with the tissues or body fluids of a plague-infected animal
  • By inhaling infectious airborne droplets from persons or animals, especially cats, with plague pneumonia
  • By laboratory exposure to plague bacteria

Ref: http://www.dhpe.org/infect/plague.html

Thursday, September 22, 2011

Where is plague found?

Plague is found in some semi-arid areas in Asia, Eastern Europe, Africa, South America, and North America. In the United States, most cases in humans occur in two regions: 1) northern New Mexico, northern Arizona, and southern Colorado, and 2) California, southern Oregon, and far western Nevada.

In the southwestern United States, rock squirrel fleas are the most common source of infection in people. In the Pacific states, California ground squirrel fleas are the most common source. Many other types of rodents -- including other ground squirrels, prairie dogs, chipmunks, wood rats, wild mice, and voles -- suffer plague outbreaks and are occasional sources of human infection. Domesticates can be infected by fleas or by eating infected wild rodents and can be a direct source of infection to people. Dogs rarely suffer severe illness and have yet to be shown to be sources of infection for humans.

Ref: http://www.dhpe.org/infect/plague.html

Sunday, September 18, 2011

What is Plague


Plague is a severe and potentially deadly bacterial infection. It is caused by the enterobacteria Yersinia pestis, named after the French-Swiss bacteriologist Alexandre Yersin. Primarily carried by rodents (most notably rats) and spread to humans via fleas, the disease is notorious throughout history, due to the unrivaled scale of death and devastation it brought. Until June 2007, plague was one of only three diseases specifically reportable to the World Health Organization (the two other ones were cholera and yellow fever). Depending on lung infection, or sanitary conditions, plague also can be spread in the air, by direct contact, or by contaminated undercooked food or materials. The symptoms of plague depend on the concentrated areas of infection in each person: such as bubonic plague in lymph nodes, septicemic plague in blood vessels, pneumonic plague in lungs, and so on. Medicines can cure plague if detected early. Plague is still endemic in some parts of the world.


Saturday, September 10, 2011

Mass Burials

"The plight of the lower and most of the middle classes was even more pitiful to behold. Most of them remained in their houses, either through poverty or in hopes of safety, and fell sick by thousands. Since they received no care and attention, almost all of them died. Many ended their lives in the streets both at night and during the day; and many others who died in their houses were only known to be dead because the neighbours smelled their decaying bodies. Dead bodies filled every corner. Most of them were treated in the same manner by the survivors, who were more

Citizens of Tournai bury plague victims. These are
fortunate to have coffins. Most victims
were interred in mass graves

concerned to get rid of their rotting bodies than moved by charity towards the dead. With the aid of porters, if they could get them, they carried the bodies out of the houses and laid them at the door; where every morning quantities of the dead might be seen. They then were laid on biers or, as these were often lacking, on tables.

Such was the multitude of corpses brought to the churches every day and almost every hour that there was not enough consecrated ground to give them burial, especially since they wanted to bury each person in the family grave, according to the old custom. Although the cemeteries were full they were forced to dig huge trenches, where they buried the bodies by hundreds. Here they stowed them away like bales in the hold of a ship and covered them with a little earth, until the whole trench was full."

References:
Boccaccio, Giovanni, The Decameron vol. I (translated by Richard Aldington illustrated by Jean de Bosschere) (1930); Gottfried, Robert, The Black Death (1983).

Wednesday, August 31, 2011

The Breakdown of Social Order

"One citizen avoided another, hardly any neighbour troubled about others, relatives never or hardly ever visited each other. Moreover, such terror was struck into the hearts of men and women by this calamity, that brother abandoned brother, and the uncle his nephew, and the sister her brother, and very often the wife her husband. What is even worse and nearly incredible is that fathers and mothers refused to see and tend their children, as if they had not been theirs.

Thus, a multitude of sick men and women were left without any care, except from the charity of friends (but these were few), or the greed, of servants, though not many of these could be had even for high wages, Moreover, most of them were coarse-minded men and women, who did little more than bring the sick what they asked for or watch over them when they were dying. And very often these servants lost their lives and their earnings. Since the sick were thus abandoned by neighbours, relatives and friends, while servants were scarce, a habit sprang up which had never been heard of before. Beautiful and noble women, when they fell sick, did not scruple to take a young or old man-servant, whoever he might be, and with no sort of shame, expose every part of their bodies to these men as if they had been women, for they were compelled by the necessity of their sickness to do so. This, perhaps, was a cause of looser morals in those women who survived."

http://www.eyewitnesstohistory.com/plague.htm


Thursday, August 25, 2011

Varying Reactions to Disaster

"...Such fear and fanciful notions took possession of the living that almost all of them adopted the same cruel policy, which was entirely to avoid the sick and everything belonging to them. By so doing, each one thought he would secure his own safety.

Some thought that moderate living and the avoidance of all superfluity would preserve them from the epidemic. They formed small communities, living entirely separate from everybody else. They shut themselves up in houses where there were no sick, eating the finest food and drinking the best wine very temperately, avoiding all excess, allowing no news or discussion of death and sickness, and passing the time in music and suchlike pleasures. Others thought just the opposite. They thought the sure cure for the plague was to drink and be merry, to go about singing and amusing themselves, satisfying every appetite they could, laughing and jesting at what happened. They put their words into practice, spent day and night going from tavern to tavern, drinking immoderately, or went into other people's houses, doing only those things which pleased them. This they could easily do because everyone felt doomed and had abandoned his

A plague victim reveals
the telltale buboe on
his leg. From a
14th century illumination

property, so that most houses became common property and any stranger who went in made use of them as if he had owned them. And with all this bestial behaviour, they avoided the sick as much as possible.

In this suffering and misery of our city, the authority of human and divine laws almost disappeared, for, like other men, the ministers and the executors of the laws were all dead or sick or shut up with their families, so that no duties were carried out. Every man was therefore able to do as he pleased.

Many others adopted a course of life midway between the two just described. They did not restrict their victuals so much as the former, nor allow themselves to be drunken and dissolute like the latter, but satisfied their appetites moderately. They did not shut themselves up, but went about, carrying flowers or scented herbs or perfumes in their hands, in the belief that it was an excellent thing to comfort the brain with such odours; for the whole air was infected with the smell of dead bodies, of sick persons and medicines.

Others again held a still more cruel opinion, which they thought would keep them safe. They said that the only medicine against the plague-stricken was to go right away from them. Men and women, convinced of this and caring about nothing but themselves, abandoned their own city, their own houses, their dwellings, their relatives, their property, and went abroad or at least to the country round Florence, as if God's wrath in punishing men's wickedness with this plague would not follow them but strike only those who remained within the walls of the city, or as if they thought nobody in the city would remain alive and that its last hour had come."


http://www.eyewitnesstohistory.com/plague.htm

Sunday, August 21, 2011

The Signs of Impending Death

"The symptoms were not the same as in the East, where a gush of blood from the nose was the plain sign of inevitable death; but it began both in men and women with certain swellings in the groin or under the armpit. They grew to the size of a small apple or an egg, more or less, and were vulgarly called tumours. In a short space of time these tumours spread from the two parts named all over the body. Soon after this the symptoms changed and black or purple spots appeared on the arms or thighs or any other part of the body, sometimes a few large ones, sometimes many little ones. These spots were a certain sign of death, just as the original tumour had been and still remained.

No doctor's advice, no medicine could overcome or alleviate this disease, An enormous number of ignorant men and women set up as doctors in addition to those who were trained. Either the disease was such that no treatment was possible or the doctors were so ignorant that they did not know what caused it, and consequently could not administer the proper remedy. In any case very few recovered; most people died within about three days of the appearance of the tumours described above, most of them without any fever or other symptoms.

The violence of this disease was such that the sick communicated it to the healthy who came near them, just as a fire catches anything dry or oily near it. And it even went further. To speak to or go near the sick brought infection and a common death to the living; and moreover, to touch the clothes or anything else the sick had touched or worn gave the disease to the person touching. "

Wednesday, August 17, 2011

The Black Death, 1348

Coming out of the East, the Black Death reached the shores of Italy in the spring of 1348 unleashing a rampage of death across Europe unprecedented in recorded history. By the time the epidemic played itself out three years later, anywhere between 25% and 50% of Europe's population had fallen victim to the pestilence.

The plague presented itself in three interrelated forms. The bubonic variant (the most common) derives its name from the swellings or buboes that appeared on a victim's neck, armpits or groin. These tumors could range in size from that of an egg to that of an apple. Although some survived


The Plague's Progress
the painful ordeal, the manifestation of these lesions usually signaled the victim had a life expectancy of up to a week. Infected fleas that attached themselves to rats and then to humans spread this bubonic type of the plague. A second variation - pneumonic plague - attacked the respiratory system and was spread by merely breathing the exhaled air of a victim. It was much more virulent than its bubonic cousin - life expectancy was measured in one or two days. Finally, the septicemic version of the disease attacked the blood system.

Having no defense and no understanding of the cause of the pestilence, the men, women and children caught in its onslaught were bewildered, panicked, and finally devastated.




Ref: http://www.eyewitnesstohistory.com/plague.htm

Saturday, August 13, 2011

The Black Plague_My nest Focus

The Black Death, or The Black Plague, was one of the most deadly pandemics in human history. It probably began in Central Asia and spread to Europe by the late 1340s. The total number of deaths worldwide from the pandemic is estimated at 75 million people; there were an estimated 20 to 30 million deaths in Europe alone. The Black Death is estimated to have killed between one-third and two-thirds of Europe’s population. [Wikipedia]

Monday, August 8, 2011

Frequently Asked Questions on Chikungunya


1. What is Chikungunya?

Chikungunya is a viral disease transmitted through mosquito bites. It is usually seen in tropical areas.

2. Who can get infected with Chikungunya?

Anyone can get infected with Chikungunya virus. The virus infection can be serious in new borns and in old people.

3. What are the symptoms of Chikungunya?

Main symptoms are high fever and joint pains. Joint pains can persist even long after recovery from the disease.

4. After infection, how soon I will see symptoms?

Chikungunya symptoms are seen after 1 to 12 days of infection. In rare cases, no symptoms are seen. The symptoms get worse in case of old people.

5. Is there any treatment for Chikungunya?

There are no vaccines or medicines for Chikungunya. Medication is done to reduce symptoms and pain.

6. How can I prevent Chikungunya infection?

Chikungunya is transmitted by mosquito. Taking various steps to minimize mosquito bite is the only effective prevention technique.

7. Can I get Chikungunya from another person?

No. Direct human to human transmission is not possible. The disease is transmitted from one person to another only through mosquito bites.

8. Is Chikungunya fatal?

No. Human immune system is capable of recovery from this disease in almost all cases. But it might take a while for the symptoms to disappear, especially the joint pains. But the outbreak at Reunion island is suspected to have caused 200 deaths. The risk is higher for older people.

9. What is the impact of Chikungunya infection during pregnancy?

Pregnant woman can get Chikungunya infection at any stage of pregnancy. The chances of passing the infection to fetus is very less. If the pregnant woman is infected at the time of delivery, the virus can be transmitted to the new born child. If a new born is infected the risk is considerably higher. So it is important to ensure that in Chikungunya areas pregnant woman is protected from mosquito bite.

10. Is it ok to breast feed if the mother is infected with Chikungunya?

Currently there is no evidence that Chikungunya virus is transmitted through breast milk. Again the best defence for the child is to use mosquito nets and repellents to reduce the risk of mosquito bite.

http://www.chikungunya.in

Wednesday, August 3, 2011

Prevention of Chikungunya

We are yet to find a vaccine for Chikungunya. The good news is that a number of Chikungunya vaccines are in experimental stage. Currently the only way to prevent Chikungunya disease to avoid mosquito bites! Chikungunya virus spreads from human to human only through mosquito carrier. Hence mosquito breeding control is the best way to fight Chikungunya.

http://www.chikungunya.in

Sunday, July 31, 2011

Treatment of Chikungunya

There is no antiviral drug or medicine specifically for Chikungunya. But since chikungunya is cured by immune system in almost all cases there is no need to worry. Treatment usually is for the symptoms and include taking sufficient rest, taking more fluid food and medicines to relieve pain (paracetamol for example). Aspirin should be avoided.
Alternative medical systems such as ayurveda and homeopathy has specific treatments for Chikungunya. Many of these treatments are helpful in reducing the symptoms especially the joint pain.

http://www.chikungunya.in

Thursday, July 28, 2011

Chikungunya Symptoms

Chikungunya typically starts with one or more of the following symptoms - chills, fever, vomiting, nausea, head ache and joint pain. The attack is sudden and sometimes it is accompanied with rashes. Severe joint pain is the main and the most problematic symptom of Chikungunya.
Other less commonly seen symptoms include mouth ulcers, loss of taste and conjunctivitis. The fever usually subsides in a couple of days, but other symptoms may last for a longer duration. In some cases joint pain persisted for years.

http://www.chikungunya.in

Monday, July 25, 2011

What causes Chikungunya Fever?


Chikungunya disease is a viral disease transmitted in humans by the bite of infected mosquitoes. Aedes aegypti mosquito (also called yellow fever mosquito) is the primary transmission agent of Chikungunya Virus. This is usually found in tropics and hence Chikungunya is predominantly seen in asian countries. In recent cases, another mosquito species named Aedes albopictus is found to be a carrier. Aedes aegypti bites during day time and hence day time mosquito bite is the main reason for transmission.
Presence of stagnated water in and around human inhabitation is one of the main causes of increased aedes mosquito population. This in turn causes a large number of mosquito bites leading to the rapid spread of Chikungunya virus.

http://www.chikungunya.in

Saturday, July 23, 2011

History of Chikungunya Disease


Chikungunya (pronounced as chiki-en-GUN-yah) disease was first detected in 1952 in africa at a place called Makonde Plateau. This is a border area between Tanzania and Mozambique. The name "chikungunya" is from the Makonde language and its meaning is "that which bends up". This is a reference to the Chikungunya symptom where patients walk in a stooped posture due to joint pain. Chikungunya is also known as Chicken guinea, Chicken gunaya and Chickengunya. The presence of the word Chicken has also lead to a lot of misconceptions about the disease.

Chikungunya outbreaks are usually recorded within an interval of 7-8 years. Between 1960 and 1980 a number of outbreaks were reported from Asia and Africa. It made a comeback in recent years and is now being reported regularly from India, Indonesia, Maldives and Thailand. In 2006, a large outbreak of Chikungunya was reported from La RĂ©union Island (France) with estimates of over 100,000 people infected and 200 deaths. In 2010, many cases were reported from Delhi. Due to its non fatal nature, a large number of Chikungunya infections go unreported.

http://www.chikungunya.in

Tuesday, July 19, 2011

What is Chikungunya?


Chikungunya is a viral disease spread by mosquitoes. Chikungunya symptoms include severe and persistent joint pain, body rash, headache and fever. Initial symptoms are similar to dengue fever. It is usually NOT life threatening. But the joint pains can last for a long time and full recovery may take months. Usually patient gets life long immunity from infection and hence re-infection is very rare.

ref: http://www.chikungunya.in


Monday, January 11, 2010

Chikungunya: next focus

I was out of station for some time and unable to continue posts and update my blog here. But now I am back and hope to carry forward my blog with good posts. You can personally ask me any questions regarding human disease and I will try my level best to clear your minds regarding disease facts. In recent times a disease called Chikungunya is making a lot of headlines and many of us do not even know the name of the disease. So I have thought to give some insight on this disease in my following posts. I hope that will be of some help regarding understanding the disease. Thank you everybody for the support and comments I got from others in the past & hope to receive the same in the future.

Wednesday, October 7, 2009

Vaccination to prevent TB

Vaccine which is used against TB infection is BCG. The BCG vaccine contains a live but weakened form of Mycobacterium bovis, which is one of the bacterium that causes tuberculosis (see previous posts). The vaccine is known as BCG vaccine because a strain of bacterium known as Bacillus Calmette-Guerin is used in this process. The vaccine is used to prevent tuberculosis and works by stimulating the body’s immune response to the bacteria without actually causing the disease.

Wednesday, September 16, 2009

Prevention of TB

Several points should be kept in mind regarding prevention of TB (Tuberculosis) disease. The prevention of spreading the disease from infected to healthy individual is of utmost importance. The following points may be noted in order to achieve this gaol: -

#Early detection of TB, prompt isolation and immediate treatment of the patient.
#Educating health care workers/close members of the patient about TB
#Screening health care workers/close members of the patient for TB
#Implementing effective work practices including wearing proper respiratory protection
#Preventing the spread of infectious droplets into the air by using appropriate exhaust #ventilation
#Controlling the direction of air flow to prevent air contamination adjacent to the infectious source
#Diluting the air through general ventilation
#Cleaning the air through air filtration

Tuesday, September 1, 2009

Mycobacterium tuberculosis

Staining means coloring of the bacteria for proper viewing under the microscope. It is very important part of identifying TB bacteria. Mycobacterium tuberculosis (MTB) is a slow growing aerobic bacterium that divides in every 16 to 20 hours; this is extremely slow compared to other bacteria that have division times measured in minutes. In contrast, one of the fastest growing bacteria is a strain of E. coli that can divide roughly every 20 minutes. As MTB only has one phosphorlipid outer membrane, it is classified as Gram-positive bacteria. But if a Gram stain is performed, MTB either stains very weakly Gram-positive or does not retain dye, due to high lipid content of its cell wall. MTB is a small rod shaped bacteria (Bacillus), which can withstand weak disinfectants and can survive in a dry state for weeks. Normally the bacteria can only grow inside a host, so in vitro (outside host) culture of M. tuberculosis took a long time to develop, but is now a routine laboratory procedure. MTB is identified microscopically by its staining characteristics; it retains certain stains often being treated with acid solution & thus is classified as an “acid-fast bacillus” or AFB. This can also be visualized by fluorescent microscopy and by an auramine-rhodomine stain.

Friday, July 31, 2009

Treatment of TB

Treatment for TB uses antibiotics to kill bacteria. The two antibiotics most commonly used are rifampicin and isoniazid. However, these treatments are more difficult than the short courses of antibiotics used to cure most other bacterial infections as long periods of treatments (around 6 to 12 months) are needed to entirely eliminate mycobacterium from the body. Latent TB treatment usually uses a single antibiotic, while active TB disease is best treated with combinations of several antibiotics to reduce the risk of the bacteria developing antibiotic resistance. People with latent infections are treated to prevent them from progressing to active TB disease later in life. Treatment using rifampicin & pyrazinamide (often used) is also not always risk free. It may cause liver damage & death due to combination of these drugs.

Friday, July 10, 2009

What is microbiology?

Since I am writing on human disease, we have to deal a lot with microbes as infectious diseases are caused by microorganisms. So I am giving a small introduction about microbiology for clear understanding of common people.
Biology is the branch of science that deals with living organisms and microbiology is a part of biology. Microbiology deals with the microscopic organisms. They include bacteria, yeasts, molds, algae & protozoa. By microscopic it means that the organism can only be seen with the aid of microscope. If an object has a diameter of less than 0.1 mm, human eye cannot perceive it. In fact anything less than 1 mm cannot be properly perceived by our eye. So organisms, whose diameter falls below 1 mm, can be regarded roughly as microorganisms & fall under the domain of microbiology. For long these organisms were not known to human being for this reason. After the invention of microscope at early seventeenth century, this new world of biology has evolved and by far this is biggest community of life. In fact all the other groups of organisms (i.e. the macro world) together do not have the number or diversity and abundance as possessed by microorganisms.
Microscopes in the early stages were of two kinds - the first was simple microscope with a single lens of very short focal length consequently capable of high magnification (just like magnifying glasses of modern world). The second one was known as compound microscope with double lens system & hence completely displaced the simple one in modern world. But in early stages the compound microscopes were full of various optical defects render them less effective than simple microscope with very short focal length (although it is extremely difficult to produce a simple microscope with that short focal length). It takes a lot of skill to make such simple microscopes.
Now everybody may think that it is not possible to see bacteria or other microbes through naked eye. It is not possible to see a bacterium off course, but you can definitely visualize them when they are in clusters. The distinction of microbes as plants or animals are not very strong. Many of them specially the bacteria are closely resemble plants in many ways. So they can be seen as unicellular plants, but many of them has no similarity with plants or may have similarity with animals. Most of them are prokaryotes (has primitive cell) but many are eukaryotes (cells with prominent nucleus) as well. Microorganisms usually possess only one cell i.e. they are unicellular organisms. For their small size they have a very high ratio of surface area to volume, which is approximately 200,000 times greater than a similar ratio for an adult human being. They absorb nutrients through their body surfaces & have high metabolic rates & rapid rate of multiplication, which results in proliferation of a certain species in small time. This way they can affect an environment enormously in very short time. This particular aspect of microbes is very important in its interaction with higher organisms. This ability can be used very efficiently for detection of pollution in the environment or can be a detrimental factor while producing disease of mankind/other useful animals (but if the disease is against an organism harmful to human then it can be regarded as a beneficial issue also).
In modern classification of living kingdom bacteria has been placed separately. There are three groups —- Archea, Bacteria and Eukaryota. Archea & Bacteria are definitely microorganisms. But some of the eukaryotes are also microbes as they are unicellular. All the bacteria have prokaryotic cell, whereas the eukaryotes have eukaryotic cell. Archea have something common of both bacteria and eukaryota.
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