Microbial disease and application of microbiology

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  • Microorganism is defined as a microbiological entity, cellular or non- cellular, which is capable of replication or transferring genetic materials.
  • Microorganisms are classified into four risk groups, based on the degree of hazard to individuals, communities and the environment. They are:
  • Risk Group 1 (no or low individual or community risk): The microorganisms that are unlikely to cause any human or animal disease are grouped under the Risk Group I. eg E. coli, Saccharomyces cerevisae, Adeno associated virus etc.
  • Risk Group 2 (moderate individual risk or low community risk): The pathogens that are likely to cause diseases on human beings or animals but unlikely to be a serious hazard to laboratory workers, community, livestock or the environment fall in this group.eg Herpes virus, Diptheria, Ringworm, Measles etc.
  • Risk Group 3 (high individual risk, low community risk): A pathogen that usually causes a serious human disease or animal disease but does not spread from one infected individual to another is categorized in this group. Effective treatment and preventive measures are available. Eg Vibrio cholerae, HIV, Mycobacterium tuberculosis, SARS etc
  • Risk Group 4 (high individual and community risk): A pathogen that usually causes a serious human disease or animal disease and that can be transmitted from one individual to another falls in this group. Effective treatment and preventive measures are not usually available. Eg Ebola virus, Marburg virus, Lassa virus, Corona virus etc
  • Health: According to WHO, Health is define as the state of complete physical, mental and social well being and not merely an absence of any disease or infirmity.
  • Disease: It is defined as any change from the normal state that causes discomfort or disability or disturbs the health. All human diseases are broadly classified into two groups. i.e Congenital diseases and acquired diseases.
  • Congenital diseases: Congenital diseases are anatomical or physiological abnormalities present in the person from birth. eg sickle cell anaemia, diabetes mellitus, haemophilia etc.
  • Acquired disease: These diseases are acquired by the person during his life time. Acquired disease are further classified into two groups.
  • Communicable diseases: The disease which transmit from one person to another person is called communicable diseases. These diseases are caused by microorganism. Eg Tuberculosis, Typhoid, Chicken pox etc.
  •  Non- Communicable diseases: The disease which are not transmit from one person to another person is called Non- communicable disease. eg Cancer, Arthritis, Mental disorder etc

  • Typhoid (Enteric Fever)
  •   It is highly communicable disease caused by bacteria.

  •   It is an acute infection of intestine.
  •   It is most most common in those area where sanitation and hygiene is not properly maintained.
  •   It is one of the most common disease in Nepal specially during rainy seasons.
  •   Causative agent: It is caused by bacterium Salmonella typhi. It is rod shaped, flagellated, gram negative bacteria having size 1- 1.5μm in length.
  •   Mode of infection: It is transmitted through faeco-oral route i.e. transmitted through food, water that is contaminated with faeces or urine.
  • Incubation period: It is a period between the entry of pathogen to first appearance of sign and symptoms. I.P is ranging from 1-3 weeks (average about 2 weeks).
  • Symptoms
  •   Constant high fever lasting for 1-3 weeks
  •   Intestine shows lesions, hemorrhage & ulceration
  •   Loss of appetite
  •   Nausea and vomiting
  •   Enlargement of spleen, abdominal tenderness
  •   Rose spots appears on the trunk.
  •   Intestinal discomfort such as constipation and diarrhea (Constipation is more common than diarrhea
  • Laboratory diagnosis
  •   Widal test: It is the test that detect antibody present in the patient serum.
  •   Blood and stool culture
  • Treatment
  • Chloramphenicol, Ampicillin, Ciprofloxacin, Cotrimoxazole Prevention and control
  • Proper sanitation and personal cleanliness
  • Sanitary disposal of human excreta
  • Protection and purification of water
  • Protection of water and food from microorganism, flies etc Immunization with TAB vaccine.

  • Tuberculosis(TB) is a highly communicable chronic bacterial disease.
  •   It primarily affects lungs and cause pulmonary tuberculosis.
  •   Tuberculosis remains a worldwide public health problem because

  • one third of the world's population is infected with TB.
  •   In Nepal about 45% of the total population is infected with TB.

  • Types of TB: There are two types of TB on the basis of site of infection.
    •   Pulmonary TB: Site of infection is lungs only
    •   Extra pulmonary TB: Site of infection is other parts or organ except lungs such as bone, kidney, lymph gland, meninges, skin etc.
    • Causative agent: It is caused by Mycobacterium tuberculosis. Which is rod shaped acid fast bacilli.

    • Mode of infection
    • It is an airborne disease so transmitted through droplet infection.
    •   Ingestion of infected milk of diseased cows may also infect healthy people.
    •   It is also transmitted from infected mother to fetus (trans placental route).

    • Incubation period
    • It is quite variable ranging from some weeks to years.
    • Symptoms

    • Persistent cough for more than 2 weeks.
    • Chest pain
    • Mild fever (especially temperature rise in the evening) Sweating at night
    • Loss of appetite and weight loss
    • Appearance of blood in sputum
    • Diagnosis
    • Chest X-ray
    • Tuberculin or Montoux test
    • Ziehl-Neelsen staining of sputum specimen
    • Culture of sputum and other specimen
    • Genetic test(PCR, Gene xpert) 
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