Microorganism: the influenza virus belonging to the Orthomyxoviridae family

Disease: influenza or flu

Occurrence of the disease

History: numbers of pandemics (worldwide epidemics) of influenza have caused many deaths. Influenza epidemics are generally associated with mortality rates of ten to 20%; this can rise to more than 50% in “enclosed” populations, such as boarding schools. The pandemics of 1889, 1918, 1957, and 1968 were devastating. The pandemic of 1918-1919 caused 21 million deaths throughout the world.

Current situation: the World Health Organization (WHO) watches this virus very closely. WHO attempts to identify new strains of the virus in order to produce a vaccine each year that will reduce the likelihood of a new pandemic.

Mechanism of action of the microorganism: once it is in our lungs, the virus breaks down the lung’s protective coating, and attaches itself to the epithelial cells of the respiratory system. The symptoms of influenza are due to the death of epithelial cells. Read More

Microorganism: the influenza virus belonging to the Orthomyxoviridae family

Disease: influenza or flu

Occurrence of the disease

History: numbers of pandemics (worldwide epidemics) of influenza have caused many deaths. Influenza epidemics are generally associated with mortality rates of ten to 20%; this can rise to more than 50% in “enclosed” populations, such as boarding schools. The pandemics of 1889, 1918, 1957, and 1968 were devastating. The pandemic of 1918-1919 caused 21 million deaths throughout the world.

Current situation: the World Health Organization (WHO) watches this virus very closely. WHO attempts to identify new strains of the virus in order to produce a vaccine each year that will reduce the likelihood of a new pandemic.

Mechanism of action of the microorganism: once it is in our lungs, the virus breaks down the lung’s protective coating, and attaches itself to the epithelial cells of the respiratory system. The symptoms of influenza are due to the death of epithelial cells.

Symptoms of the disease: flu symptoms are characterized by chills, headache, fever, and generalized muscle aches. The flu lasts between three and seven days, and symptoms similar to those of a cold develop. During this period, the fever drops. Normally, influenza is not fatal, but secondary bacterial infections (Staphylococcus aureus or Streptococcus pneumoniae) can cause death from pneumonia. Therefore, most deaths attributable to the influenza virus are in fact caused by secondary infections. These complications are more frequent in elderly people.

Incubation period: one to two days

Contagious period: the contagious period is from three to five days following the onset of symptoms in adults, and up to seven days after onset among children.

Hosts: humans, but especially birds and pigs; these may be the source of new infectious strains of influenza for humans.

Transmission: large quantities of virus are found in the nasal secretions of an infected person. The disease can therefore be spread by aerosols, that is, through the air.

Treatment: new antiviral medications are effective in reducing symptoms. Patients are advised to get plenty of sleep. One antiviral medication, amantadine, reduces the symptoms of type A influenza. However, this substance produces numerous side effects, such as insomnia and difficulty in concentrating.

Geographical distribution of the microorganism: worldwide

Prevention: since the 1940s, killed-virus vaccines (viruses incapable of infecting) have been used to control influenza. These vaccines are administered particularly to persons over the age of 65, as well as to those with chronic illnesses. The composition of the vaccine is reassessed each year.

Vaccine: each year, the inactivated vaccine is reformulated to ensure its effectiveness against the most dangerous strains of the virus identified by the WHO.

It is very difficult to produce vaccines each year that are effective against the influenza virus; this virus undergoes antigenic modification, that is, it changes its form and the immune system is no longer capable of recognizing it.


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

Influenza virus

Photo : Robert Alain

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


Microorganism: this virus is a member of the genus Morbillivirus of the family Paramyxoviridae.

Disease: measles

Occurrence of the disease

History: following the launch of a widespread vaccination program in 1966, the number of cases of measles has decreased by 98%.

Current situation: between 2,000 and 3,000 cases of measles are reported each year in the United States. However, 90% of these occur in non-vaccinated people. In the developing countries without vaccination programs, 220,000 deaths from measles occur each year. In 1994 the industrialized countries undertook to eradicate the spread of measles by the end of the year 2005. In Canada only 16 cases of measles were reported in 1998.

Mechanism of action of the microorganism: the measles virus enters the organism via the respiratory system or the ocular conjunctiva (eyes) and multiplies within the cells in the lung. From there it enters the bloodstream and travels to different organs, including the skin.

Symptoms of the disease: Read More

Microorganism: this virus is a member of the genus Morbillivirus of the family Paramyxoviridae.

Disease: measles

Occurrence of the disease

History: following the launch of a widespread vaccination program in 1966, the number of cases of measles has decreased by 98%.

Current situation: between 2,000 and 3,000 cases of measles are reported each year in the United States. However, 90% of these occur in non-vaccinated people. In the developing countries without vaccination programs, 220,000 deaths from measles occur each year. In 1994 the industrialized countries undertook to eradicate the spread of measles by the end of the year 2005. In Canada only 16 cases of measles were reported in 1998.

Mechanism of action of the microorganism: the measles virus enters the organism via the respiratory system or the ocular conjunctiva (eyes) and multiplies within the cells in the lung. From there it enters the bloodstream and travels to different organs, including the skin.

Symptoms of the disease: the first signs of the disease are nasal secretions, fever, cough, headaches, and conjunctivitis. These are followed by eruptions of the skin, rash and eruptions of the mucous membranes in the mouth. These spots in the mouth, which are red with a blue and white center, are called Koplik’s spots.

Incubation period: ten to 14 days

Contagious period: the contagious period lasts from four days before until four days after the appearance of the rash.

Hosts: humans

Tranmission: this is a very contagious disease.

Treatment: no specific treatment

Geographical distribution of the microorganism: before immunization, measles was present throughout the world. Massive immunization programs have considerably reduced the rate of measles infection in industrialized countries.

Prevention: vaccine

Vaccine: the vaccine against measles is attenuated. This vaccine is combined with vaccines against rubella and mumps. This vaccine is called MMR and the injections are recommended at 12 and 18 months. Ninety-nine per cent of those vaccinated with the two recommended doses are protected against measles.


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

Microorganism: the mumps virus is part of the Paramyxoviridae family.

Disease: mumps

Occurrence of the disease

History: vaccination against mumps started in 1967

Current situation: 3,000 cases of mumps are reported in the United States each year. Lately there has been an increase in this disease affecting those children who have not been vaccinated. In 1998, 117 cases of mumps were reported in Canada.

Mechanism of action of the microorganism: the virus first multiplies in the respiratory system and then circulates in the blood throughout the organism.

Symptoms of the disease: the most important symptoms are swelling and pain in the salivary glands. A mild fever occurs. In certain cases, complications of mumps can include meningitis or an inflammation of the testicles.

Incubation period: 14 to 25 days

Contagious period: the contagious period lasts from five to seven days before and up to nine days after the appearance of the disease. Read More

Microorganism: the mumps virus is part of the Paramyxoviridae family.

Disease: mumps

Occurrence of the disease

History: vaccination against mumps started in 1967

Current situation: 3,000 cases of mumps are reported in the United States each year. Lately there has been an increase in this disease affecting those children who have not been vaccinated. In 1998, 117 cases of mumps were reported in Canada.

Mechanism of action of the microorganism: the virus first multiplies in the respiratory system and then circulates in the blood throughout the organism.

Symptoms of the disease: the most important symptoms are swelling and pain in the salivary glands. A mild fever occurs. In certain cases, complications of mumps can include meningitis or an inflammation of the testicles.

Incubation period: 14 to 25 days

Contagious period: the contagious period lasts from five to seven days before and up to nine days after the appearance of the disease.

Hosts: humans

Transmission: the virus is spread through the saliva of infected individuals, and enters through the respiratory system. This disease is very contagious.

Treatment: none

Geographical distribution of the microorganism: worldwide, but absent in restricted populations such as isolated tribes.

Prevention: vaccine

Vaccine: the vaccination against mumps is combined with the vaccines against measles and rubella in a vaccine called MMR. Two injections are necessary in children aged 12 and 18 months. This vaccination is 99% effective in people who have had both doses.


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

The measles and the mumps are members of the genus Morbillivirus of the family Paramyxoviridae.

Photo : Robert Alain

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


Microorganism: Epstein-Barr virus (EBV)

Disease: mononucleosis

Occurrence of the disease

Mechanism of action of the microorganism: the virus enters the lymphatic tissue and infects the B cells of the immune system. The infected cells multiply and take on a characteristically deformed appearance that allows diagnosis of the disease.

The Epstein-Barr virus also causes Burkitt’s lymphoma, a malignant tumor. This was the first type of cancer to be associated with a viral infection.

Symptoms of the disease: enlargement of the lymph nodes and spleen, sore throat, headache, nausea, and generalized fatigue.

Incubation period: four to six weeks

Contagious period: if the virus remains in the secretions of the pharynx, contagious period may persist for more than one year.

Host: humans

Transmission: this disease, which is not highly contagious, can be transmitted from mouth to mouth – hence the name “kissing disease.” Read More

Microorganism: Epstein-Barr virus (EBV)

Disease: mononucleosis

Occurrence of the disease

Mechanism of action of the microorganism: the virus enters the lymphatic tissue and infects the B cells of the immune system. The infected cells multiply and take on a characteristically deformed appearance that allows diagnosis of the disease.

The Epstein-Barr virus also causes Burkitt’s lymphoma, a malignant tumor. This was the first type of cancer to be associated with a viral infection.

Symptoms of the disease: enlargement of the lymph nodes and spleen, sore throat, headache, nausea, and generalized fatigue.

Incubation period: four to six weeks

Contagious period: if the virus remains in the secretions of the pharynx, contagious period may persist for more than one year.

Host: humans

Transmission: this disease, which is not highly contagious, can be transmitted from mouth to mouth – hence the name “kissing disease.”

Treatment: none. Rest is generally recommended.

Geographical distribution of the microorganism: worldwide

Prevention: avoid contact with sick persons

Vaccine: not available


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

Haemophilus influenzae

Illustration by Bruno Laporte

© Illustration by Bruno Laporte


Microorganism: poliomyelitis virus, the polio virus, is part of the Picornaviridae family.

Disease: poliomyelitis or polio

President Roosevelt of the United States contracted poliomyelitis as an adult. He was never able to walk normally afterwards.

Occurrence of the disease

History: several hieroglyphic drawings which date from around 2000 BC show people with small arms and legs (atrophy), leading us to believe that poliomyelitis already existed at that time. Before the development of the vaccine in 1955, between 15,000 and 20,000 cases of poliomyelitis were reported each year in the United States.

Current situation: Cases of poliomyelitis are extremely rare in Canada.

Forecast: The eradication of poliomyelitis is predicted for the year 2004.

Mechanism of action of the microorganism: the virus enters the cells of the throat and the intestine to multiply. Subsequently it invades the tonsils and lymph nodes of the neck. In certain cases, the virus may enter the bloodstream causi Read More

Microorganism: poliomyelitis virus, the polio virus, is part of the Picornaviridae family.

Disease: poliomyelitis or polio

President Roosevelt of the United States contracted poliomyelitis as an adult. He was never able to walk normally afterwards.

Occurrence of the disease

History: several hieroglyphic drawings which date from around 2000 BC show people with small arms and legs (atrophy), leading us to believe that poliomyelitis already existed at that time. Before the development of the vaccine in 1955, between 15,000 and 20,000 cases of poliomyelitis were reported each year in the United States.

Current situation: Cases of poliomyelitis are extremely rare in Canada.

Forecast: The eradication of poliomyelitis is predicted for the year 2004.

Mechanism of action of the microorganism: the virus enters the cells of the throat and the intestine to multiply. Subsequently it invades the tonsils and lymph nodes of the neck. In certain cases, the virus may enter the bloodstream causing viremia, a viral infection of the blood.

Symptoms of the disease: this disease is asymptomatic at first. The next stage involves fever, headache, sore throat, vomiting, and a loss of appetite. In the case of an invasion of the bloodstream by the virus, it may affect the nervous system and result in paralysis.

Incubation period: usually from seven to 14 days, but this may vary between three and 35 days.

Contagious period: the transmission period lasts for as long as the virus is excreted, which corresponds to three days after the start of the infection and continues for six weeks.

Hosts: humans

Transmission: the spread of this virus occurs through contact with throat secretions or with excrement of an infected person. The virus may also be spread through food, water, or air.

Treatment: none

Geographical distribution of the microorganism: before immunization, poliomyelitis was present throughout the world. Today poliomyelitis persists in India, as well as in west and central Africa. In the industrialized nations, poliomyelitis is now extremely rare. In the United States between five and ten cases are reported each year, caused by the oral vaccine.

Prevention: vaccine

Vaccine: attenuated vaccine (oral, Sabin) or inactive (Salk). Jonas Salk successfully immunized humans in 1953, using a vaccine that was inactivated by formaldehyde. This vaccine was officially approved in 1955. In 1962 Albert Sabin developed an attenuated vaccine that could be taken orally. The two vaccines dramatically reduced the number of cases of paralytic poliomyelitis in the majority of developed nations. The vaccine is effective in 99% of cases provided the individual receives the recommended doses. The inactivated vaccine has been used in Quebec since 1996.


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

Poliomyelitis virus

Photo : Robert Alain

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


Microorganism: a virus of the family Rhabdoviridae.

Disease: rabies

Occurrence of the disease

History: in 1885, Louis Pasteur became famous for using a vaccine he had developed to cure a young shepherd bitten by a rabid dog.

Current situation: rabies kills 35,000 to 40,000 people annually; most cases occur in developing countries. A single case of rabies, caused by a bat bite, was reported in Quebec in 2000. This was the first reported case in years.

Mechanism of action of the microorganism: the rabies virus multiplies in the salivary glands and eventually spreads to the muscles and nervous system. Once it reaches the brain, it produces masses known as Negri bodies. Because the virus grows in the salivary glands, it can be transmitted through bites.

Symptoms of the disease: anxiety, irritability, fatigue, depression, loss of appetite, and fever. More serious effects include muscle hypersensitivity, paralysis, convulsions and delirium. If untreated, the disease results in the destructio Read More

Microorganism: a virus of the family Rhabdoviridae.

Disease: rabies

Occurrence of the disease

History: in 1885, Louis Pasteur became famous for using a vaccine he had developed to cure a young shepherd bitten by a rabid dog.

Current situation: rabies kills 35,000 to 40,000 people annually; most cases occur in developing countries. A single case of rabies, caused by a bat bite, was reported in Quebec in 2000. This was the first reported case in years.

Mechanism of action of the microorganism: the rabies virus multiplies in the salivary glands and eventually spreads to the muscles and nervous system. Once it reaches the brain, it produces masses known as Negri bodies. Because the virus grows in the salivary glands, it can be transmitted through bites.

Symptoms of the disease: anxiety, irritability, fatigue, depression, loss of appetite, and fever. More serious effects include muscle hypersensitivity, paralysis, convulsions and delirium. If untreated, the disease results in the destruction of the part of the brain responsible for the control of breathing.

Incubation period: three to eight weeks.

Contagious period: in cats and dogs, usually three to seven days.

Hosts: wild animals such as skunks, raccoons, bats, and foxes are the most common hosts for rabies, although cats and dogs may also act as hosts.

Transmission: rabies is transmitted through contact with the saliva or blood of infected animals, most commonly through bites.

Treatment: bites from rabid animals should be immediately washed with soap and water. Consult a hospital emergency department as soon as possible, to obtain vaccination against rabies. While vaccines are usually preventive rather than curative, the long incubation period of rabies allows this vaccine to actually prevent the development of the disease.

Geographical distribution of the disease: worldwide.

Prevention: vaccination of pets and, in some cases, immunization of wild animals through the use of oral vaccines. For example, a mass immunization program of wild animals around the Canada-United States border has been undertaken, using air-dropped food containing an oral vaccine.

Vaccine: inactivated vaccine.


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

Rabies virus

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.

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