Microorganism: the molds Trichophyton rubrum, T. mentagrophytes var. interdigitale, and Epidermophyton floccosum.

Disease: athlete's foot

Mechanism of action of the microorganism: the molds usually multiply between the toes, where the warm, humid, and dark environment provides ideal growth conditions. The molds responsible for athlete's foot form spores and so are very resistant.

Symptoms of the disease: peeling of the skin in thin strips (desquamation), usually between the toes. Itching may be experienced.

Incubation period: unknown.

Contagious period: as long as the condition persists or the molds survive in contaminated materials (shower, bath, socks).

Hosts: humans.

Transmission: direct contact with lesions or with a contaminated surface.

Treatment of the disease: any of a number of fungicides, e.g., clotrimazole. Frequent airing out of the feet.

Geographical distribution of the microorganism Read More

Microorganism: the molds Trichophyton rubrum, T. mentagrophytes var. interdigitale, and Epidermophyton floccosum.

Disease: athlete's foot

Mechanism of action of the microorganism: the molds usually multiply between the toes, where the warm, humid, and dark environment provides ideal growth conditions. The molds responsible for athlete's foot form spores and so are very resistant.

Symptoms of the disease: peeling of the skin in thin strips (desquamation), usually between the toes. Itching may be experienced.

Incubation period: unknown.

Contagious period: as long as the condition persists or the molds survive in contaminated materials (shower, bath, socks).

Hosts: humans.

Transmission: direct contact with lesions or with a contaminated surface.

Treatment of the disease: any of a number of fungicides, e.g., clotrimazole. Frequent airing out of the feet.

Geographical distribution of the microorganism: worldwide.

Prevention: strict personal hygiene, including careful drying of the area between the toes after baths and showers. Application of an appropriate antifungal powder on the feet; regular cleaning of the bath and shower, especially if infected individuals are using them.

Vaccine: none.


© Armand-Frappier Museum, 2008. All rights reserved.

Trichophyton rubrum

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the parasites Plasmodium falciparum, Plasmodium vivax

Disease: malaria, paludism

Occurrence of the disease

History: malaria is the infectious disease that has had the most impact on humans, notably contributing to the fall of the Greek and Roman empires. Ancient Chinese and Hindi texts mention this disease, describing the fever and chills that are typical of malaria. Several researchers, from Hippocrates at the end of the Vth century BC to Ronald Ross in 1902, studied malaria to finally demonstrate that this disease is transmitted by mosquitoes. This explained why people exposed to swampy environments were often affected. In 1955, the Word Health Organization began a malaria eradication program, which was largely unsuccessful: the mosquitoes became increasingly resistant to the insecticides and the parasites became increasingly resistant to medication.

Current situation: In most temperate zones as well as in several sub-tropical regions, malaria has either never existed or has been eradicated. However, it rema Read More

Microorganism: the parasites Plasmodium falciparum, Plasmodium vivax

Disease: malaria, paludism

Occurrence of the disease

History: malaria is the infectious disease that has had the most impact on humans, notably contributing to the fall of the Greek and Roman empires. Ancient Chinese and Hindi texts mention this disease, describing the fever and chills that are typical of malaria. Several researchers, from Hippocrates at the end of the Vth century BC to Ronald Ross in 1902, studied malaria to finally demonstrate that this disease is transmitted by mosquitoes. This explained why people exposed to swampy environments were often affected. In 1955, the Word Health Organization began a malaria eradication program, which was largely unsuccessful: the mosquitoes became increasingly resistant to the insecticides and the parasites became increasingly resistant to medication.

Current situation: In most temperate zones as well as in several sub-tropical regions, malaria has either never existed or has been eradicated. However, it remains one of the most important diseases in nearly all tropical countries. Worldwide, more than 100 million individuals are infected annually and nearly one million of them die.

Mechanism of action of the microorganism: the bite of a Plasmodium-infected mosquito allows the parasite to get into the bloodstream. It travels to the liver to reproduce and then invades the oxygen-carrying blood cells. When the parasite is in the bloodstream, it can be picked up by another mosquito, which can spread the disease to new individuals by biting them.

Symptoms of the disease: fever, cough, chills, sweating, diarrhea, and headaches. Furthermore, the disease can evolve toward renal, pulmonary, or cerebral problems and can even lead to coma and death.

Incubation period: seven to 14 days

Contagious period: a mosquito can transmit malaria during its entire life. In humans, the parasite can be transmitted to mosquitoes for about a year.

Hosts: humans and mosquitoes

Transmission: transmission occurs through the bite of a mosquito of the genus Anopheles. The bite allows the insect to ingest contaminated blood. When the mosquito bites another human, it liberates the parasite into the individual’s blood.

Certain populations of west Africa are resistant to malaria. The hemoglobin of these individuals has a mutation that makes it impossible for the malaria-causing parasite to reproduce. Unfortunately, this mutation is responsible for a disease called falciform anemia, which is accompanied by chronic fatigue. Not an interesting choice to make!

Discoverer or the microorganism: Laveran in 1880

Treatment: chloroquine, if the diagnosis is rapid.

Geographical distribution of the microorganism: the forests of South America, southeast Asia and the southern Sahara in Africa.

Prevention: eliminate the breeding grounds of anopheles mosquitoes when they are near human populations. Administer chloroquine or mefloquine preventively. It is also recommended to use insecticides, to install mosquito nets around the bed and to close the windows in the evening and at night.

Vaccine: not available


© Armand-Frappier Museum, 2008. All rights reserved.

Plasmodium falciparum

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: prion

Disease: Creutzfeldt-Jakob

Occurrence of the disease

Current situation: At the end of the 1950s, the American neurologist, Carleton Gajdusek, was vacationing in Australia where, according to some of his colleagues, a tribe from Papua - New Guinea was affected by a disease known as kuru. Gajdosek went to Papua and settled there to study the disease. In the tribe’s language, the word kuru means “to tremble.” Victims of the disease generally lost control of their movements and died three months to a year after the appearance of the first symptoms. Women were more affected than men (3:1) and children, regardless of their sex, were more affected than were adults.

Autopsies of the brains of people affected by kuru revealed holes in their neurons (spongiform encephalopathy). Gajdusek then discovered that the members of the tribe practiced a post-mortem ritual: cannibalism. The causal agent for the disease, located mostly in the brain, was transmitted through this ritual. Certain parts of the deceased Read More

Microorganism: prion

Disease: Creutzfeldt-Jakob

Occurrence of the disease

Current situation: At the end of the 1950s, the American neurologist, Carleton Gajdusek, was vacationing in Australia where, according to some of his colleagues, a tribe from Papua - New Guinea was affected by a disease known as kuru. Gajdosek went to Papua and settled there to study the disease. In the tribe’s language, the word kuru means “to tremble.” Victims of the disease generally lost control of their movements and died three months to a year after the appearance of the first symptoms. Women were more affected than men (3:1) and children, regardless of their sex, were more affected than were adults.

Autopsies of the brains of people affected by kuru revealed holes in their neurons (spongiform encephalopathy). Gajdusek then discovered that the members of the tribe practiced a post-mortem ritual: cannibalism. The causal agent for the disease, located mostly in the brain, was transmitted through this ritual. Certain parts of the deceased, such as the muscles, were reserved for the men. The brain and the internal organs were reserved for women and children. When cannibalism was discontinued, kuru disappeared.

By searching the literature, William Hadlow discovered that humans suffering from Creutzfeldt-Jakob disease, fatal familial insomnia, and Gerstmann-Straussler-Scheinker disease showed the same symptoms. Furthermore, the symptoms of scrapie and mad cow disease were also identical. In fact, the same type of agent causes all these diseases: prions.

Mechanism of action of the microorganism: prions are mainly found in brain neurons (message transmitters and receptors) and in neurons of the central nervous system (certain types of nerves). The cellular protein PrPc is normally present in the nervous systems of animals. In the presence of PrPsc (sc for scrapie, the term used to designate the disease caused by prions in sheep), PrPc undergoes a change in conformation to become an infectious protein itself: a prion.

Symptoms of the disease: confusion, motor disturbances (lack of coordination), dementia, nervous tics, memory impairment, insomnia, etc.

Incubation period: from 15 months to 30 years

Contagious period: the tissues of the central nervous system are contagious while symptoms are present but a few studies have shown that the disease may be transmissible even before the symptoms appear.

Hosts: humans and possibly animals

Transmission: poorly defined. Often, propagation is associated with the transplantation or the injection of infected tissues. Some researchers also believe that the consumption of meat containing prions responsible for mad cow disease can lead to Creutzfeldt-Jakob disease.

Mad cow disease is often associated with Creutzfeldt-Jakob disease because prions are responsible for both diseases. Because the inter-species incubation period is between ten and 40 years, it will take some time before we are able to attribute Creutzfeldt-Jakob disease to the ingestion of prion-contaminated bovine meat.

Discoverer of the microorganism: Stanley B. Prusiner

Treatment: none

Geographical distribution of the microorganism: this disease has been reported worldwide

Prevention: being very careful, during organ transplantation, to avoid using tissue infected with prions. In Canada, we do not accept blood donors who have recently spent time in England.

Vaccine: not available


© Armand-Frappier Museum, 2008. All rights reserved.

Creutzfeldt-Jakob

Illustration by Bruno Laporte

© Illustration by Bruno Laporte


Microorganism: the protozoa Giardia lamblia

Disease: giardia

Occurrence of the disease

History: van Leeuwenhoek, the inventor of the microscope, discovered this microorganism while he was examining his own feces.

Current situation: in Canada and in the United States, the giardia microorganism is endemic in day care centers. In 1998, 5,519 cases of giardia were registered in Canada of which 983 were in the province of Quebec. Worldwide, nearly 200 million people are infected.

Mechanism of action of the microorganism: the microorganism lives in the environment in the form of a cyst. It enters the body following absorption of contaminated water and moves down to the intestines where the cyst breaks open. The microorganism then attaches itself to the intestinal wall and invades the intestine while multiplying. An accumulation of these microorganisms in the intestines can hinder food absorption.

Symptoms of the disease: some people are asymptomatic, i.e., they have no symptoms. Others, Read More

Microorganism: the protozoa Giardia lamblia

Disease: giardia

Occurrence of the disease

History: van Leeuwenhoek, the inventor of the microscope, discovered this microorganism while he was examining his own feces.

Current situation: in Canada and in the United States, the giardia microorganism is endemic in day care centers. In 1998, 5,519 cases of giardia were registered in Canada of which 983 were in the province of Quebec. Worldwide, nearly 200 million people are infected.

Mechanism of action of the microorganism: the microorganism lives in the environment in the form of a cyst. It enters the body following absorption of contaminated water and moves down to the intestines where the cyst breaks open. The microorganism then attaches itself to the intestinal wall and invades the intestine while multiplying. An accumulation of these microorganisms in the intestines can hinder food absorption.

Symptoms of the disease: some people are asymptomatic, i.e., they have no symptoms. Others, however, have serious diarrhea, cramps, and considerable flatulence, which often lead to weight loss.

Giardia can be either acute or chronic. Intermittent diarrhea is a symptom of chronic giardia.

Incubation period: three to 25 days

Contagious period: the whole duration of the infection. This may extend over several months.

Hosts: humans and possibly rodents, cervidae (deer), cattle, and domestic animals. In Quebec, a large proportion of cattle is infected with Giardia lamblia and they contaminate water with their feces.

Transmission: the microorganism is transmitted through contaminated water.

Discoverer of the microorganism: van Leeuwenhoek

Treatment: some medications exist, such as mepacrine hydrocloride, metronidazole or furazolidone.

Geographical distribution of the microorganism: worldwide

Prevention: adequate treatment of water reserves

Vaccine: not available


© Armand-Frappier Museum, 2008. All rights reserved.

Giardia lamblia

Photo : Joel Mancuso

© Joel Mancuso


Microorganism: the protozoan Toxoplasma gondii

Disease: toxoplasmosis. Toxoplasmosis is also known by other names: litter box disease and sandbox disease.

Occurrence of the disease

History: this disease attracted public attention when it became known that some severe congenital malformations, and even fetal death, were associated with it.

Current situation: today, toxoplasmosis is often involved in the death of persons suffering from AIDS.

Mechanism of action of the microorganism: the microbe enters the host through the oral or fecal route. It eventually attacks several organs, such as the lungs, heart, liver, and the retina of the eye. The immune system normally overcomes this infection.

However, the organism may form resistant cysts in some organs. When an infected individual's immune system weakens, the organism may start to multiply again and cause illness.

Symptoms of the disease: except in cases of congenital malformations or fetal death, most affected people do not hav Read More

Microorganism: the protozoan Toxoplasma gondii

Disease: toxoplasmosis. Toxoplasmosis is also known by other names: litter box disease and sandbox disease.

Occurrence of the disease

History: this disease attracted public attention when it became known that some severe congenital malformations, and even fetal death, were associated with it.

Current situation: today, toxoplasmosis is often involved in the death of persons suffering from AIDS.

Mechanism of action of the microorganism: the microbe enters the host through the oral or fecal route. It eventually attacks several organs, such as the lungs, heart, liver, and the retina of the eye. The immune system normally overcomes this infection.

However, the organism may form resistant cysts in some organs. When an infected individual's immune system weakens, the organism may start to multiply again and cause illness.

Symptoms of the disease: except in cases of congenital malformations or fetal death, most affected people do not have symptoms (they are asymptomatic). Symptoms that may eventually appear are swelling of lymph nodes or symptoms associated with mononucleosis.

Incubation period: ten to 20 days following consumption of undercooked meat; five to 20 days in the case of contamination by an infected cat.

Contagious period: this disease does not spread from person to person, except from a mother to her child. However, the organisms excreted by an affected cat are infectious for one to five days following excretion. Moreover, the microorganism can survive in water for more than one year.

Hosts: cats, dogs, cattle, sheep, and humans.

Transmission: transmission is generally through the fecal or oral route. However, the disease can also be spread through ingestion of raw meat, by blood transfusion, by organ transplantation, or from mother to child.

Treatment: there are medications for treating toxoplasmosis, such as pyrimethamine and sulfadiazine.

Geographical distribution of the microorganism: worldwide

Prevention: avoid consumption of raw meat; wash hands after gardening; clean cat litter boxes regularly and wash hands afterwards; keep pet cats indoors, and feed them commercial cat food.

Vaccine: no vaccine available


© Armand-Frappier Museum, 2008. All rights reserved.

Toxoplasma gondii

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Microorganism: the protozoan Trypanosoma

Disease: trypanosomiasis (sleeping sickness)

Occurrence of the disease

Current situation: because these protozoa can cause very serious diseases in humans as well as in animals, the World Health Organization has mobilized many resources in the search for a vaccine against Trypanosoma. In Canada, no cases of trypanosomiasis were reported in 1998.

Mechanism of action of the microorganism: as soon as the parasite enters the bloodstream, it multiplies. The protozoan then invades the central nervous system and causes lesions.

Symptoms of the disease: a deep lethargy, saliva traces around the mouth, and insensitivity to pain.

There is an American equivalent to this disease known as American tripanosomiasis or Chagas’ disease. The symptoms differ (generalized discomfort, fever, and liver problems), but it is caused by the same type of protozoan, namely Trypanosoma.

Incubation period: the incubation period lasts between t Read More

Microorganism: the protozoan Trypanosoma

Disease: trypanosomiasis (sleeping sickness)

Occurrence of the disease

Current situation: because these protozoa can cause very serious diseases in humans as well as in animals, the World Health Organization has mobilized many resources in the search for a vaccine against Trypanosoma. In Canada, no cases of trypanosomiasis were reported in 1998.

Mechanism of action of the microorganism: as soon as the parasite enters the bloodstream, it multiplies. The protozoan then invades the central nervous system and causes lesions.

Symptoms of the disease: a deep lethargy, saliva traces around the mouth, and insensitivity to pain.

There is an American equivalent to this disease known as American tripanosomiasis or Chagas’ disease. The symptoms differ (generalized discomfort, fever, and liver problems), but it is caused by the same type of protozoan, namely Trypanosoma.

Incubation period: the incubation period lasts between three days and many years, depending on the strain of protozoan that has infected the person.

Contagious period: an infected fly can propagate the disease as long as it lives. Animals can transmit the parasite to flies as long as they transport the protozoa in their blood.

Hosts: tsetse flies, humans, and certain domesticated and wild animals.

Transmission: transmission occurs when tsetse flies, infected by the protozoa, bite animals (including humans).

Treatment: many drugs, such as suramin, melarsoprol and eflornithine

Geographical distribution of the microorganism: the protozoan is confined to tropical Africa and it follows the distribution of the tsetse fly.

Prevention: protection against bites from tsetse flies.

Vaccine: not available


© Armand-Frappier Museum, 2008. All rights reserved.

Trypanosoma

Armand-Frappier Museum

© Armand-Frappier Museum, 2008. All rights reserved.


Microorganism: the yeast Candida albicans.

Disease: thrush.

Occurrence of the disease

History: descriptions of mouth lesions resembling thrush date back as far as the 1800s. In 1839, Bernard Langenbeck described the microorganism responsible for thrush, the yeast we know today as Candida albicans. The prevalence of candidiases (infections caused by C. albicans) increased once antibiotics began to be widely used for other conditions. This phenomenon is thought to be due to the antibiotics' ability to kill the bacteria that normally inhibit the growth of Candida. Freed from the inhibiting effect of the bacteria, the yeast grows unfettered.

Mechanism of action of the microorganism: Thrush is rather common among newborns, as they have not yet developed a balanced natural microbial flora. Candida albicans may cause many other candidiases, depending on the organ it infects. Vaginitis, for example, is a C. albicans infection.

C. albicans is naturally present in the Read More

Microorganism: the yeast Candida albicans.

Disease: thrush.

Occurrence of the disease

History: descriptions of mouth lesions resembling thrush date back as far as the 1800s. In 1839, Bernard Langenbeck described the microorganism responsible for thrush, the yeast we know today as Candida albicans. The prevalence of candidiases (infections caused by C. albicans) increased once antibiotics began to be widely used for other conditions. This phenomenon is thought to be due to the antibiotics' ability to kill the bacteria that normally inhibit the growth of Candida. Freed from the inhibiting effect of the bacteria, the yeast grows unfettered.

Mechanism of action of the microorganism: Thrush is rather common among newborns, as they have not yet developed a balanced natural microbial flora. Candida albicans may cause many other candidiases, depending on the organ it infects. Vaginitis, for example, is a C. albicans infection.

C. albicans is naturally present in the respiratory tract and mouth of most people, and the vagina of most women. The yeast causes no problem in healthy individuals, as its numbers are controlled by naturally occurring microorganisms. If the natural balance between these microorganisms and Candida is perturbed, the virus may multiply, producing a candidiasis such as thrush.

Symptoms of the disease: small white plaques, usually observed on the tongue and in the mouth.

Incubation period: two to five days.

Contagious period: as long as lesions are present.

Hosts: humans.

Transmission: direct contact with oral, dermal or vaginal secretions or excretions from infected individuals. Transmission may also occur from mother to infant during birth.

Treatment of the disease: nystatin and azole, both taken orally.

Geographical distribution of the microorganism: worldwide.

Prevention: disinfection of beds in nurseries, in order to avoid transmission of thrush from one infant to another.

Vaccine: none.


© Armand-Frappier Museum, 2008. All rights reserved.

Candida albicans

Dennis Kunkel Microscopy, Inc.

© Dennis Kunkel Microscopy, Inc.


Learning Objectives

The learner will:
  • familiarize himself with the vocabulary used in microbiology;
  • explain the relationship between developments in imaging technology and the current understanding of the cell;
  • identify which microorganisms are infectious, how the immune system fights against them, and the reinforcements of modern medicine;
  • describe the benefits of microorganisms.

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