Microorganism: human immunodeficiency virus (HIV), genus: Lentivirus, family: Retroviridae.

Disease: acquired immunodeficiency syndrome (AIDS)

Occurrence of the disease

History: in 1978, the Centers for Disease Control in Atlanta observed pneumonia and a very rare form of cancer known as Kaposi's sarcoma in some individuals. These patients also exhibited a reduced immune response characterized by a heightened sensitivity to infection and a reduction in the number of cells known as T lymphocytes. In 1981, this disease was identified as AIDS. The disease appears to have begun to spread in central Africa in the 1950s, and a virus that may be the ancestor of the AIDS virus has been isolated from African green monkeys.

Current situation: AIDS is the first worldwide pandemic of the last half of the 20th century. In 1997, it affected 0.13-0.5% of the Canadian population. Every day, 16,000 new cases of HIV infection are recorded around the world. In 1998, 138 cases of AIDS were reported in Quebec.

Projections Read More

Microorganism: human immunodeficiency virus (HIV), genus: Lentivirus, family: Retroviridae.

Disease: acquired immunodeficiency syndrome (AIDS)

Occurrence of the disease

History: in 1978, the Centers for Disease Control in Atlanta observed pneumonia and a very rare form of cancer known as Kaposi's sarcoma in some individuals. These patients also exhibited a reduced immune response characterized by a heightened sensitivity to infection and a reduction in the number of cells known as T lymphocytes. In 1981, this disease was identified as AIDS. The disease appears to have begun to spread in central Africa in the 1950s, and a virus that may be the ancestor of the AIDS virus has been isolated from African green monkeys.

Current situation: AIDS is the first worldwide pandemic of the last half of the 20th century. In 1997, it affected 0.13-0.5% of the Canadian population. Every day, 16,000 new cases of HIV infection are recorded around the world. In 1998, 138 cases of AIDS were reported in Quebec.

Projections: the World Health Organization estimates that 50-100 million people will be infected with AIDS by 2003.

Mechanism of action of the microorganism: the virus first binds to immune system cells known as T lymphocytes. It then enters the cells and multiplies, killing the cells. Because T lymphocytes are one of the body's primary defenses against disease, people infected with HIV develop diseases, known as opportunistic infections, which are usually not dangerous for other people.

There are two types of HIV: HIV-1 and HIV-2. HIV-2 is much less dangerous than HIV-1. HIV preferentially infects CD4+ T lymphocytes. The receptor for the virus is CD4+ and its co-receptors are CXCR4 and CCR5. Individuals who have mutated forms of the genes responsible for the CCR5, CXCR4, CCR2 or SDF-1 molecules are resistant to the disease's development or progression.

Although the virus has occasionally been found in saliva, tears and urine, there have been no reported cases of transmission by contact with these fluids.

Symptoms of the disease: in 1996, 67% of patients diagnosed with a typical AIDS opportunistic infection had survived at least 24 months. By 1998, this rate had increased to 77%, thanks to improvements in the nature and availability of treatments for AIDS and opportunistic diseases.

Incubation of period: variable. Virus antibodies are usually detectable in the blood one to three months after exposure. Symptoms generally appear one to 15 years after HIV infection.

Contagious period: unknown, but several specialists believe that it begins immediately following infection and lasts throughout the infected person's lifetime.

Hosts: humans.

Transmission: heterosexual and homosexual sexual relations, contact with contaminated blood (e.g., during transfusions and the exchange of contaminated syringes by drug users). Transmission from women to children is possible during childbirth or nursing.

Discoverer of the microorganism: Montagnier and Gallo in 1983.

Treatment of the disease: although there is no miracle cure, some drugs may improve patients' quality of life and prolong their lives. These drugs prevent the virus from multiplying, by inhibiting three viral enzymes: inverse transcriptase, protease and integrase. The use of these three inhibitors together is known as triple therapy.

Geographic distribution of the microorganism: worldwide.

Prevention: use of latex condoms with a high-risk partner or with multiple partners. Screening of sexual partners. Use of sterile syringes by intravenous drug users. Screening of pregnant women.

Vaccine: none.


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

Human immunodeficiency virus (HIV)

Photo : Robert Alain

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


Microorganism: rhinoviruses of the family Picornaviridae, which account for more than 30% of colds.

Disease: colds

Occurrence of the disease

Current situation: colds are common infections in humans of all ages.

Mechanism of action of the microorganism: the virus infects the nasal mucosa (the skin cells lining the inside of the nose).

Symptoms of the disease: partial obstruction of the nose, nasal discharge, throat irritation, cough, sneezing.

Incubation period: usually 48 hours.

Contagious period: 24 hours to five days.

Hosts: humans.

Transmission: contact with nasal secretions, airborne droplets generated by sneezing, and contact with contaminated objects.

Because there are a wide variety of rhinoviruses, and because other types of viruses, such as the coronaviruses, the parainfluenza virus, and adenoviruses, may also cause colds, this disease is common. Immunity against colds does not last long. Read More

Microorganism: rhinoviruses of the family Picornaviridae, which account for more than 30% of colds.

Disease: colds

Occurrence of the disease

Current situation: colds are common infections in humans of all ages.

Mechanism of action of the microorganism: the virus infects the nasal mucosa (the skin cells lining the inside of the nose).

Symptoms of the disease: partial obstruction of the nose, nasal discharge, throat irritation, cough, sneezing.

Incubation period: usually 48 hours.

Contagious period: 24 hours to five days.

Hosts: humans.

Transmission: contact with nasal secretions, airborne droplets generated by sneezing, and contact with contaminated objects.

Because there are a wide variety of rhinoviruses, and because other types of viruses, such as the coronaviruses, the parainfluenza virus, and adenoviruses, may also cause colds, this disease is common. Immunity against colds does not last long.

Treatment of the disease: none.

Geographical distribution of the microorganism: worldwide.

Prevention: regular hand washing.

Vaccine: oral vaccines containing attenuated live viruses exist for some types of cold, but are not generally available, as colds are not usually dangerous.


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

Picornaviridae

Photo : Robert Alain

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


Microorganism: group A rotavirus, a member of the Reoviridae family

Disease: gastroenteritis

Occurrence of the disease

Current situation: diarrheal diseases, which include diarrhea caused by the rotaviruses, are the most important cause of death among young children. Every year, especially in developing countries, these diseases kill between five and ten million children around the world. In the United States, the rotaviruses are responsible for 35% of cases of gastroenteritis, and for 75 to 150 deaths each year.

Mechanism of action of the microorganism: the virus attacks the cells of the intestine, thereby preventing them from carrying out their function, that is, absorbing nutrients.

Symptoms of the disease: vomiting, fever, headache, and severe diarrhea causing dehydration which, in young children, necessitates hospitalization.

Incubation period: 24 to 48 hours

Contagious period: the contagious period begins during the symptomatic phase and continues until Read More

Microorganism: group A rotavirus, a member of the Reoviridae family

Disease: gastroenteritis

Occurrence of the disease

Current situation: diarrheal diseases, which include diarrhea caused by the rotaviruses, are the most important cause of death among young children. Every year, especially in developing countries, these diseases kill between five and ten million children around the world. In the United States, the rotaviruses are responsible for 35% of cases of gastroenteritis, and for 75 to 150 deaths each year.

Mechanism of action of the microorganism: the virus attacks the cells of the intestine, thereby preventing them from carrying out their function, that is, absorbing nutrients.

Symptoms of the disease: vomiting, fever, headache, and severe diarrhea causing dehydration which, in young children, necessitates hospitalization.

Incubation period: 24 to 48 hours

Contagious period: the contagious period begins during the symptomatic phase and continues until about the eighth day following infection.

Hosts: humans

Transmission: fecal and oral routes

Discoverer of the microorganism:

Treatment: treatment consists of giving large quantities of fluids to the patient to prevent dehydration. Viral gastroenteritis normally disappears of its own accord.

Geographical distribution of the microorganism: worldwide

Prevention: vaccine

Vaccine: in 1998, a live vaccine (RRV-TV) against the rotavirus was approved for use in the United States. This vaccine can be given orally. RRV-TV was withdrawn from the market in 1999 because it caused intussuceptions (penetration of one part of an organ into an immediately adjoining part, like a glove turned inside out) among newborns. The vaccine caused intestinal invagination, which in turn provoked obstruction of the intestines.


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

Diarrheal diseases, which include diarrhea caused by the rotaviruses, are the most important cause of death among young children.

Photo : Robert Alain

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


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.

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans