Microorganism: the virus responsible for chicken pox and shingles (VZV or varicella-zoster virus) is a member of the Herpesviridae family.

Disease: chickenpox

Occurrence of the disease: in 1998, 180 cases of chickenpox were reported in Canada, but since this is not a notifiable disease, this number does not accurately reflect the true situation.

Mechanism of action of the microorganism: the virus is inhaled and then develops in the respiratory system. Anyone who has had chickenpox is subsequently immune to the disease. Nevertheless, the virus stays dormant in the host, remaining in the nerves of the back. If such a person is weakened, due to infection by the AIDS virus, for example, or because of a psychological or physiological shock, the virus can multiply and cause another disease known as shingles. Shingles usually appears in adults over the age of 50.

Symptoms of the disease: fever, skin rash resembling small pimples on the face and upper body. These pimples fill with pus and eventually form scabs. Severe itching accompanies Read More

Microorganism: the virus responsible for chicken pox and shingles (VZV or varicella-zoster virus) is a member of the Herpesviridae family.

Disease: chickenpox

Occurrence of the disease: in 1998, 180 cases of chickenpox were reported in Canada, but since this is not a notifiable disease, this number does not accurately reflect the true situation.

Mechanism of action of the microorganism: the virus is inhaled and then develops in the respiratory system. Anyone who has had chickenpox is subsequently immune to the disease. Nevertheless, the virus stays dormant in the host, remaining in the nerves of the back. If such a person is weakened, due to infection by the AIDS virus, for example, or because of a psychological or physiological shock, the virus can multiply and cause another disease known as shingles. Shingles usually appears in adults over the age of 50.

Symptoms of the disease: fever, skin rash resembling small pimples on the face and upper body. These pimples fill with pus and eventually form scabs. Severe itching accompanies this disease. The mortality rate is lower among children (1/100,000) than among adults (1/5,000).

Incubation period: ten to 23 days

Contagious period: the contagious period begins five days before the appearance of the skin rash and continues until there are scabs on all lesions, or about five days after the rash begins.

Hosts: humans

Transmission: chickenpox is a very contagious skin disease that usually affects children from the ages of two to seven. It is spread by direct contact, or by droplets of respiratory secretions.

Chickenpox is one of the most contagious diseases, particularly among children under ten years of age. This viral infection remains latent, and disease may recur years later as herpes zoster in about 15% of older adults, and sometimes in children.

Treatment: a treatment exists based on an antiviral substance called acyclovir.

Geographical distribution of the microorganism: worldwide

Prevention: isolation of affected individuals and use of a vaccine against chickenpox.

Vaccine: a live attenuated vaccine, Varivax, has been approved for use in the United States since 1995 and in Canada since 1999.


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

Virus responsible for chicken pox

Photo : Robert Alain

© Robert Alain, SME, INRS-Institut Armand-Frappier


Microorganism: herpes simplex type 1 virus, family: Herpesviridae.

Disease: cold sores

Occurrence of the disease

History: Hippocrates, the ancient Greek physician, described the symptoms of cold sores in approximately 400 BC.

Current situation: this virus is the greatest cause of blindness in the United States. It is estimated that 50-90% of all adults in the world have been infected by this virus.

Mechanism of action of the microorganism: the virus attacks skin cells, most commonly of the lips, mouth or gums. The accumulation of the virus and of dead cells causes blisters to form. The virus remains present even after the small eruptions caused by the virus have healed (within a week) and migrates to lymph glands, where they remain in an inactive form for the rest of the individual's life. From time to time, the virus becomes active again and reinfects the lips, mouth or gums, causing new cold sores to appear. Cold, fever, excessive sunlight, and stress appear to be triggers for the reactivation of the virus. Read More

Microorganism: herpes simplex type 1 virus, family: Herpesviridae.

Disease: cold sores

Occurrence of the disease

History: Hippocrates, the ancient Greek physician, described the symptoms of cold sores in approximately 400 BC.

Current situation: this virus is the greatest cause of blindness in the United States. It is estimated that 50-90% of all adults in the world have been infected by this virus.

Mechanism of action of the microorganism: the virus attacks skin cells, most commonly of the lips, mouth or gums. The accumulation of the virus and of dead cells causes blisters to form. The virus remains present even after the small eruptions caused by the virus have healed (within a week) and migrates to lymph glands, where they remain in an inactive form for the rest of the individual's life. From time to time, the virus becomes active again and reinfects the lips, mouth or gums, causing new cold sores to appear. Cold, fever, excessive sunlight, and stress appear to be triggers for the reactivation of the virus.

Symptoms of the disease: eruptions (blisters) around the mouth, lips or gums. In serious cases, the virus may infect the cornea (the transparent covering of the eye), causing a condition known as herpetic keratitis that may cause a loss of vision.

Incubation period: two to 12 days.

Contagious period: two to seven weeks.

Hosts: humans.

Transmission: direct contact with cold sores.

Treatment of the disease: acyclovir and vidarabine are antiviral agents that partially eradicate the virus.

Geographical distribution of the microorganism: worldwide.

Prevention: avoidance of kissing individuals with cold sores.

Vaccine: none.


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

Microorganism: the herpes simplex type 2 virus belongs to the family Herpesviridae

Disease: genital herpes

Occurrence of the disease

History: in the United States, genital herpes can be found in 20 to 30% of adults. This rate increases dramatically (to more than 60%) among people with several sexual partners.

Mechanism of action of the microorganism: the virus penetrates inside the cell and multiplies, causing an immune system reaction that gives rise to sores. When the sores heal, the virus withdraws to neighboring nerve cells from where it returns periodically to re-infect the genitals.

Symptoms of the disease: fever, burning sensation, pain in the genitals. Some sores can appear and disappear on the penis and in the vagina. A large quantity of viruses is produced inside these sores.

Incubation period: about one week

Contagious period: the contagious period is intermittent. It is often associated with the presence of sores but these are not required for th Read More

Microorganism: the herpes simplex type 2 virus belongs to the family Herpesviridae

Disease: genital herpes

Occurrence of the disease

History: in the United States, genital herpes can be found in 20 to 30% of adults. This rate increases dramatically (to more than 60%) among people with several sexual partners.

Mechanism of action of the microorganism: the virus penetrates inside the cell and multiplies, causing an immune system reaction that gives rise to sores. When the sores heal, the virus withdraws to neighboring nerve cells from where it returns periodically to re-infect the genitals.

Symptoms of the disease: fever, burning sensation, pain in the genitals. Some sores can appear and disappear on the penis and in the vagina. A large quantity of viruses is produced inside these sores.

Incubation period: about one week

Contagious period: the contagious period is intermittent. It is often associated with the presence of sores but these are not required for the disease to be transmitted.

Hosts: humans

Transmission: sexual contact. An infected woman can also transmit the disease to her child during childbirth. This infection, known as congenital herpes, can be fatal in newborns. This type of infection affects nearly 2,000 babies per year in the United States.

The sores heal in a few weeks but small quantities of the virus remain. This is why the sores reappear periodically for no apparent reason. Some researchers believe that stress, fever, or sunlight can cause the reappearance of the sores. This disease is said to be latent which means that it remains even if the affected person has no symptoms. The viruses are always present but in variable quantities.

Treatment: no treatment exists. However, some antiviral substances, such as acyclovir (Zovirax) can reduce the frequency of appearance of the sores.

Geographical distribution of the microorganism: worldwide

Prevention: use of a condom during sexual relations

Vaccine: not available


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

Cold sores, the herpes simplex type 1 virus, and genital herpes, the herpes simplex type 2 virus, are a part of the Herpesviridae family.

Photo : Robert Alain

© Robert Alain, SME, INRS-Institut Armand-Frappier


Microorganism: the Ebola virus, from the Filoviridae family

Disease: Ebola virus disease, or Ebola hemorrhagic fever

Occurrence of the disease

History: in 1976, 550 cases of Ebola virus disease were reported in Zaire and Sudan; 430 of these patients died.

Current situation: in industrialized countries, cases of Ebola virus disease are extremely rare.

Forecast: many researchers worry that under favorable circumstances, the viruses causing hemorrhagic fevers such as Ebola could cause many more casualties than the current AIDS pandemic. Our susceptibility to these viruses is one of the great weaknesses of mankind.

Mechanism of action of the microorganism: the devastating effects of the virus make it very difficult to study its mechanism of action. It is generally accepted that the destruction of tissue is a direct result of the multiplication of the virus.

Symptoms of the disease: sudden fever, discomfort, myalgia (muscle pain), headache, pharyngitis, vomiting, s Read More

Microorganism: the Ebola virus, from the Filoviridae family

Disease: Ebola virus disease, or Ebola hemorrhagic fever

Occurrence of the disease

History: in 1976, 550 cases of Ebola virus disease were reported in Zaire and Sudan; 430 of these patients died.

Current situation: in industrialized countries, cases of Ebola virus disease are extremely rare.

Forecast: many researchers worry that under favorable circumstances, the viruses causing hemorrhagic fevers such as Ebola could cause many more casualties than the current AIDS pandemic. Our susceptibility to these viruses is one of the great weaknesses of mankind.

Mechanism of action of the microorganism: the devastating effects of the virus make it very difficult to study its mechanism of action. It is generally accepted that the destruction of tissue is a direct result of the multiplication of the virus.

Symptoms of the disease: sudden fever, discomfort, myalgia (muscle pain), headache, pharyngitis, vomiting, skin rash, hemorrhage accompanied by the failure of one or more organs, death.

Incubation period: from two to 21 days

Contagious period: as long as secretions or blood contain the virus.

Hosts: unknown, in spite of much research

Transmission: person to person transmission occurs by direct contact with blood, secretions, organs, or infected serum.

Treatment: not available

Geographical distribution of the microorganism: Africa

Prevention: isolation of infected individuals

Vaccine: not available


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

Ebola hemorrhagic fever

Illustration by Bruno Laporte

© Illustration by Bruno Laporte


Microorganism: this virus is an hepatovirus from the Picornaviridae family.

Disease: hepatitis A

Occurrence of the disease

Current situation: this disease has a low mortality rate. In 1998, 1,090 cases were reported in Canada.

Mechanism of action of the microorganism: the virus travels to the intestine where it reproduces.

Symptoms of the disease: the symptoms are usually benign. They include fever, weight loss, nausea, and abdominal discomfort. In the most severe cases, the virus can enter the bloodstream and move to the liver, the kidneys, and the spleen. However, we usually find the virus in the intestine. For this reason, feces are very infectious. Jaundice will develop if the liver is infected. The symptoms last between two and 20 days.

Incubation period: the incubation period is about 28 to 30 days.

Contagious period: the second half of the incubation period is the most contagious period and it continues a few days after the appearance of jaundice when th Read More

Microorganism: this virus is an hepatovirus from the Picornaviridae family.

Disease: hepatitis A

Occurrence of the disease

Current situation: this disease has a low mortality rate. In 1998, 1,090 cases were reported in Canada.

Mechanism of action of the microorganism: the virus travels to the intestine where it reproduces.

Symptoms of the disease: the symptoms are usually benign. They include fever, weight loss, nausea, and abdominal discomfort. In the most severe cases, the virus can enter the bloodstream and move to the liver, the kidneys, and the spleen. However, we usually find the virus in the intestine. For this reason, feces are very infectious. Jaundice will develop if the liver is infected. The symptoms last between two and 20 days.

Incubation period: the incubation period is about 28 to 30 days.

Contagious period: the second half of the incubation period is the most contagious period and it continues a few days after the appearance of jaundice when this symptom is present.

Transmission: this disease is transmitted through human feces (oral-fecal transmission). Recent epidemics in the homosexual population, intravenous drug users and handlers of contaminated foods.

It is estimated that 40 to 80% of the population of the United States has natural antibodies against this disease. This means that these people have been unknowingly in contact with the hepatitis A virus.

Hosts: humans

Treatment: no specific treatment exists

Geographical distribution of the microorganism: this disease is present worldwide, but particularly in developing countries.

Prevention: rigorous personal hygiene and an adequate water purification system. There also exists an inactivated hepatitis A vaccine.

Vaccine: an inactivated vaccine is recommended to people travelling to regions where hepatitis A is highly present. A combined hepatitis A and B vaccine is also recommended for homosexuals, intravenous drug users, and patients suffering from liver disease.


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

Hepatitis A

Illustration by Bruno Laporte

© Illustration by Bruno Laporte


Microorganism: the hepatitis B virus is a member of the family Hepadnaviridae.

Disease: hepatitis B

Occurrence of the disease

Current situation: In 1998, 970 cases of hepatitis B were reported in Canada. In industrialized countries, persons most susceptible to this virus are those who use contaminated needles for injecting intravenous drugs. Throughout the world, 200 million people suffer from a chronic infection caused by the hepatitis B virus.

Mechanism of action of the microorganism: the microorganism enters the blood and infects the hepatic cells, that is, the cells of the liver. The infection can cause the breakdown of certain blood components, which can result in jaundice.

Symptoms of the disease: most persons infected with the hepatitis B virus show no symptoms during the first six weeks, or even up to six months, following infection. After a certain period, the disease gradually becomes apparent through fever, loss of appetite, abdominal pain, nausea, and fatigue. There is often jaundice, a condition i Read More

Microorganism: the hepatitis B virus is a member of the family Hepadnaviridae.

Disease: hepatitis B

Occurrence of the disease

Current situation: In 1998, 970 cases of hepatitis B were reported in Canada. In industrialized countries, persons most susceptible to this virus are those who use contaminated needles for injecting intravenous drugs. Throughout the world, 200 million people suffer from a chronic infection caused by the hepatitis B virus.

Mechanism of action of the microorganism: the microorganism enters the blood and infects the hepatic cells, that is, the cells of the liver. The infection can cause the breakdown of certain blood components, which can result in jaundice.

Symptoms of the disease: most persons infected with the hepatitis B virus show no symptoms during the first six weeks, or even up to six months, following infection. After a certain period, the disease gradually becomes apparent through fever, loss of appetite, abdominal pain, nausea, and fatigue. There is often jaundice, a condition in which the skin becomes yellow. The disease is generally not fatal; nevertheless, in five to ten per cent of cases, the virus persists in the host for many years. A chronic, or long-term, infection may eventually cause liver cancer, or hepatocellular carcinoma. This type of cancer, while rare in the United States, is more common in certain regions of Africa and south Asia.

Incubation period: 60 to 90 days, on average

Contagious period: the contagious period begins several weeks before the appearance of symptoms and continues during the acute phase of the disease.

Hosts: humans

Transmission: through contaminated blood products or through sexual contact. The virus can also be transmitted from a mother to her baby.

Transmission by means of blood transfusion is now rare in industrialized countries, since blood is systematically tested for the presence of the hepatitis B virus at the time of donation.

Treatment: a person who believes that he or she has been in contact with contaminated blood may receive an injection of anti-hepatitis antibodies (immunoglobulins) within the next seven days.

Geographical distribution of the microorganism: worldwide

Prevention: vaccine. Use of condoms is another means of prevention, as is limiting the number of sexual partners. Good hygiene in other respects is advised, that is, regular hand washing, especially following contact with blood. Finally, one should avoid sharing syringes, razors, and even toothbrushes.

Vaccine: the vaccine against hepatitis B was the first human vaccine developed through recombinant DNA technology. This vaccine consists of a part of the virus called the surface antigen. In Quebec, elementary school children in fourth grade, as well as women with high-risk behavior, are vaccinated against hepatitis B.

Side-effects of the vaccine: in most cases, the vaccine has no side-effects. Nevertheless, some people may have redness or slight swelling at the site of the injection. Very rarely, the vaccine can cause headaches, fever, muscle pain and allergic reactions. The vaccine is effective in 90% of cases.


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

Hepadnaviridae

Illustration by Bruno Laporte

© Illustration by Bruno Laporte


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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