BNS NAMS Microbiology

 

NATIONAL ACADEMY OF MEDICAL SCIENCES

BNS FIRST YEAR FINAL EXAM 2081

LEVEL:- Bachelor in Nursing Sciences (BNS)

SUBJECT:- Microbiology / Parasitology / Virology 104-2081

1.     Discuss the modes of transmission of the dengue virus and describe the clinical features of dengue virus infection. What preventive measures can be taken to reduce the risk of dengue virus transmission?

The dengue virus is primarily transmitted to humans through the bite of infected female mosquitoes, predominantly of the species Aedes aegypti and Aedes albopictus. The transmission occurs in the following ways:

• Mosquito-Borne Transmission: Aedes mosquitoes acquire the virus by biting an infected person during their viremic phase (when the virus is present in the bloodstream). The infected mosquito becomes a carrier and can transmit the virus to another person during subsequent bites.
• Maternal Transmission: The virus can be transmitted from a pregnant mother to her fetus, particularly during childbirth.
• Blood Transfusion: Infected blood products can potentially transmit the virus.
• Laboratory Transmission: Accidental exposure to the virus in laboratory settings.

Clinical Features of Dengue Virus Infection

The clinical presentation of dengue virus infection can range from mild to severe and is classified into three main forms:

1. Dengue Fever (Mild Form):
• Symptoms:
• Sudden high fever (104°F or higher).
• Severe headache, retro-orbital (behind the eyes) pain.
• Muscle and joint pain ("breakbone fever").
• Rash: Initially maculopapular (flat and raised areas) followed by petechiae (small red spots).
• Nausea, vomiting, and fatigue.
• The fever typically lasts 2–7 days.
2. Dengue Hemorrhagic Fever (DHF):
• Symptoms:
• High fever with increased capillary permeability.
• Abdominal pain and persistent vomiting.
• Hemorrhagic manifestations: Nosebleeds, gum bleeding, or blood in stool/urine.
• Thrombocytopenia: Low platelet count leading to bleeding tendencies.
• Complications: Fluid leakage can lead to shock.
3. Dengue Shock Syndrome (DSS):
• The most severe form, characterized by:
• Profound shock due to severe plasma leakage.
• Organ failure and potentially fatal outcomes if untreated.

Preventive Measures to Reduce the Risk of Dengue Virus Transmission

1. Mosquito Control:
• Eliminate Breeding Sites: Remove standing water from containers, tires, pots, and gutters where mosquitoes breed.
• Insecticide Use: Apply larvicides to stagnant water and spray insecticides in high-risk areas.
2. Personal Protection:
• Wear Protective Clothing: Long-sleeved shirts and pants reduce exposure to mosquito bites.
• Use Insect Repellents: Apply repellents containing DEET, picaridin, or IR3535 on exposed skin.
• Use Bed Nets: Particularly effective in areas with high mosquito populations.
3. Community Engagement:
• Conduct public awareness campaigns on the importance of mosquito control and protection.
• Encourage community cleanup drives to eliminate mosquito habitats.
4. Structural Measures:
• Install window and door screens to prevent mosquitoes from entering homes.
• Use air conditioning to reduce mosquito activity indoors.
5. Health Surveillance:
• Monitor and report dengue cases to identify and respond to outbreaks promptly.
• Implement vector control measures in affected areas.

2.     Define antimicrobial agents. Explain the major mechanisms by which bacteria become resistant to antibiotics. (2+8=10)

Antimicrobial agents are substances that kill or inhibit the growth of microorganisms, including bacteria, viruses, fungi, and parasites. These agents can be naturally derived (e.g., antibiotics from microorganisms), synthetic, or semisynthetic. Examples include penicillin, tetracycline, and sulfonamides.

Bacteria develop resistance to antibiotics through various mechanisms. These can be categorized into intrinsic resistance (naturally occurring) and acquired resistance (developed through mutations or gene acquisition). The major mechanisms include:

1. Enzymatic Degradation or Modification of Antibiotics- Bacteria produce enzymes that inactivate antibiotics by breaking them down or modifying their structure. Examples: Beta-lactamases: Enzymes that hydrolyze the beta-lactam ring in penicillins and cephalosporins.

2. Alteration of Target Sites-  Bacteria modify the target molecule or structure that the antibiotic binds to, reducing the drug's efficacy.Examples: Methicillin-resistant Staphylococcus aureus (MRSA): Alters penicillin-binding proteins (PBPs) to resist beta-lactams.

3. Efflux Pumps- Bacteria use efflux pumps to actively expel antibiotics from the cell, reducing intracellular drug concentration.Examples: Tetracycline resistance: Efflux pumps encoded by genes like tet(A) actively transport tetracycline out of the cell.

4. Reduced Permeability- Bacteria decrease antibiotic entry by modifying or reducing the number of porin channels in the cell membrane. Examples:Gram-negative bacteria: Reduced porin expression prevents entry of beta-lactams and fluoroquinolones.

5. Bypassing Metabolic Pathways- Bacteria develop alternative pathways to bypass the antibiotic's action. Examples: Resistance to sulfonamides and trimethoprim: Bacteria acquire alternate enzymes (e.g., dihydropteroate synthase) to continue folic acid synthesis.

 

3.     List common intestinal protozoa. Describe the life cycle, pathogenesis, and laboratory diagnosis of Entamoeba histolytica.

Some common intestinal protozoa are

·  Entamoeba histolytica: Causes amoebiasis.

·  Giardia lamblia: Causes giardiasis.

·  Cryptosporidium spp.: Causes cryptosporidiosis.

 

The life cycle of E histolytica is relatively simple and consists of infective cysts and the invasive trophozoite stage. The life cycle completes in a single host, i.e, human.

Humans become infected with E. histolytica cysts from contaminated food and water. The mature Cyst is resistant to the low pH of the stomach and remains unaffected by gastric juices. The cyst wall is then lysed by intestinal trypsin, and when the cyst reaches the caecum or lower part of the ileum, excystation occurs. The neutral or alkaline environment and bile components favor excystation.

Excystation of a cyst gives 4 trophozoites.

Trophozoites are active and carried to the large intestine by the peristalsis of the small intestine.

Trophozoites then gain maturity and divide by binary fission.

The trophozoites adhere to the mucus lining of the intestine by lectin and secrete proteolytic enzymes, which cause tissue destruction and necrosis.

Parasite, when it gains access to the blood, migrates and causes extra-intestinal diseases.

When the load of trophozoites increases, some of the trophozoites stop multiplying and revert to cyst form by the process of encystation.

These cysts are released in feces, completing the life cycle.

 

Pathogenesis

a.      Invasive Amoebiasis: Trophozoites invade the intestinal mucosa, causing tissue destruction and ulceration. Leads to amoebic colitis, characterized by dysentery (bloody diarrhea) and abdominal pain.

b.    Extraintestinal Amoebiasis: Trophozoites may enter the bloodstream and disseminate to other organs, particularly the liver, causing amoebic liver abscess.

c. Virulence Factors: Adhesion molecules: Mediate attachment to the intestinal epithelium. Cytotoxins: Induce cell death and tissue damage. Proteolytic enzymes: Degrade host tissues.

 The Laboratory Diagnosis includes

• Microscopic Examination:
• Direct Wet Mount: Detect motile trophozoites or cysts in fresh stool.
• Concentrated Stool Smear: Increases the sensitivity for cyst detection.
• Culture: Stool or tissue samples can be cultured to isolate the parasite.
• Serological Tests: Detect antibodies in cases of extraintestinal amoebiasis (e.g., liver abscess).
• Molecular Methods: PCR is highly sensitive and specific, distinguishing E. histolytica from non-pathogenic species like E. dispar.
• Imaging for Extraintestinal Disease: CT or ultrasound can identify liver abscesses.

4.     Define antigen and antibody. How are neonates protected from infections before their immune system has reached maturity? (2+2+6=10)

Antigen- An antigen is a molecule, usually a protein or polysaccharide, that is recognized by the immune system as foreign. It can trigger an immune response, including the production of antibodies. Examples include toxins, components of pathogens (bacteria, viruses, fungi), and allergens.

Antibody- An antibody is a glycoprotein (also known as an immunoglobulin) produced by B cells in response to an antigen. It specifically binds to the antigen to neutralize it or mark it for destruction by immune cells.

Neonatal Protection from Infections

Neonates have an immature immune system at birth, making them vulnerable to infections. However, they are protected by passive immunity and other mechanisms until their immune system matures.

1. Maternal Antibodies (Passive Immunity)

• During pregnancy, maternal IgG antibodies are transferred across the placenta to the fetus via the neonatal Fc receptor (FcRn).
• These antibodies provide protection against infections the mother has encountered.
• Levels are highest at birth but decline over the first few months of life.

2. Breastfeeding

• Colostrum (the first milk) and breast milk provide antibodies, mainly IgA.
• IgA protects the mucosal surfaces of the respiratory and gastrointestinal tracts.
• Breast milk also contains immune cells, cytokines, and antimicrobial proteins like lactoferrin and lysozyme.

3. Innate Immunity

• Neonates rely on innate immune mechanisms, including:
• Phagocytic cells (e.g., neutrophils, macrophages).
• Complement proteins for pathogen lysis.
• Physical barriers like the skin and mucous membranes.

4. Vaccination-

• Early immunization helps stimulate the neonate’s adaptive immune system against specific pathogens (e.g., BCG for tuberculosis, Hepatitis B vaccine).

5. Write short notes on: (any two) (5 x 2 = 10)

a. Normal flora and their functions in the human body

b. Superficial mycoses

c. Safety Precaution in Microbiology lab

a. Normal flora, also known as microbiota, refers to the group of microorganisms (bacteria, fungi, and viruses) that reside on or in the human body without causing harm under normal conditions. Examples- Skin: Staphylococcus epidermidis, Gastrointestinal Tract: Escherichia coli, Lactobacillus.

Functions:

·       The normal flora synthesize and excrete vitamins in excess of their own needs, which can be absorbed as nutrients by their host. For example, in humans, enteric bacteria secrete Vitamin K and Vitamin B12, and lactic acid bacteria produce certain B-vitamins.

 

·       The normal flora prevent colonization by pathogens by competing for attachment sites or for essential nutrients. 

·      
The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species. The intestinal bacteria produce a variety of substances like fatty acids and peroxides to highly specific bacteriocins, which inhibit or kill other bacteria. 

·       The normal flora stimulate the development of certain tissues, i.e., the caecum and certain lymphatic tissues (Peyer's patches) in the GI tract.

 

·       The normal flora stimulate the production of natural antibodies. Since the normal flora behave as antigens in an animal, low levels of antibodies produced against components of the normal flora are known to cross react with certain related pathogens, and thereby prevent infection or invasion. 

 b. Superficial Mycoses

Superficial mycoses are fungal infections that affect the outermost layers of the skin, hair, and nails without invading deeper tissues.

Common Types:

1. Tinea Versicolor: Caused by Malassezia species, leading to hypo- or hyperpigmented patches on the skin.
2. Tinea Nigra: Caused by Hortaea werneckii, resulting in dark patches on the palms or soles.
3. Black Piedra: Affects the hair shaft, caused by Piedraia hortae.
4. White Piedra: Affects the hair, caused by Trichosporon species.

Treatment:

• Topical antifungal agents (e.g., ketoconazole, terbinafine).
• Good hygiene practices to prevent recurrence.

c. Safety Precautions in a Microbiology Lab

Safety precautions are required to prevent contamination, infection, and accidental exposure to potentially harmful microorganisms.

Major Precautions:

1.     Personal Protective Equipment (PPE):

• Wear lab coats, gloves, and masks.
• Use eye protection when handling hazardous materials.

2.     Sterilization and Disinfection:

• Use autoclaves to sterilize equipment and culture media.
• Disinfect work surfaces before and after use.

3.     Proper Handling of Specimens:

• Avoid direct contact with samples.
• Use aseptic techniques to transfer cultures.

4.     Waste Disposal:

• Dispose of biological waste in designated biohazard bins.
• Sharps (e.g., needles) must be discarded in puncture-proof containers.

5.     Behavioral Practices:

• No eating, drinking, or smoking in the lab.
• Tie back long hair and avoid touching the face.

6.     Emergency Procedures:

• Know the location of eyewash stations and fire extinguishers.
• Report all accidents and spills immediately.