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.

B.Sc. Nursing questions (NAMS)

 

 B.Sc. Nursing questions (NAMS)

1.     Describe the pathogenesis and laboratory diagnosis of Shigella infection

2.     What do you understand by the term infective endocarditis? List various organisms causing infective endocarditis.

3.     What do you know about the word septicemia? List various organisms that cause septicemia. Describe the laboratory diagnosis of septicemia.

4.     Name various organs causing urinary tract infections. Describe the sample collection and diagnosis of urinary tract infection.

5.     List causative agents of sexually transmitted infections. State the diagnosis of syphilis.

6.     List out the causative agents of meningitides. Describe the clinical features and diagnosis of bacterial meningitis

7.     Write short notes on vaginal discharge and systemic mycoses

8.     Write the biochemical findings in the case of bacterial meningitis

9.     What are the various methods of culturing microorganisms?

10.  List the causative agents of UTI. Describe different methods of urine sample collection.

11.  List causative agents of infective endocarditis. Describe the diagnosis of infective endocarditis.

12.  List causative agents of diarrhoea and describe the lab diagnosis of Salmonella gastroenteritis.

13.  Describe the pathogenesis and laboratory diagnosis of malaria.

14.  What is this sterilization? List different methods of sterilization and disinfection with examples?

15.  Describe the pathogenesis, clinical features, and laboratory diagnosis of malaria

16.  Define bacteria and write about the factors promoting the growth of bacteria

17.  Name for common respiratory pathogens. Describe the collection and transport of respiratory specimens for microbiological diagnosis

18.  List Causative agents of diarrhea. Describe Salmonellosis.

19.  Difference between a live vaccine and a killed vaccine

20.  Principles and uses of the autoclave

21.  State the common urine specimen and their collection methods.

22.  List the various types of reproductive tract infection with the names of common pathogens. How will you diagnose syphilis in the laboratory?

 

 

Herpes virus

 

Herpes virus

Herpes viruses are DNA viruses; they are the leading cause of human viral disease, second only to influenza and cold viruses. Herpes (Latin herpes, Greek herpein, which means to creep). This reflects the creeping or spreading nature of the skin lesions caused by many herpes virus types. It is capable of causing overt disease or remaining silent for many years, only to be reactivated, for example, as shingles.

The Herpesviridae family is a large group of double-stranded DNA viruses. They are classified into three subfamilies: Alpha, Beta, and Gamma herpesviruses.

1. Alpha-herpesviruses (α-herpesvirinae)

• Characteristics:
• Rapid replication cycle
• Latency in sensory nerve ganglia
• Broad host range
• Examples:
• Herpes simplex virus type 1 (HSV-1) → oral herpes
• Herpes simplex virus type 2 (HSV-2) → genital herpes
• Varicella-zoster virus (VZV / HHV-3) → chickenpox (primary), shingles (reactivation)

2. Beta-herpesviruses (β-herpesvirinae)

• Characteristics:
• Slow replication cycle
• Latency in monocytes, lymphocytes, kidney, secretory glands
• Cause enlargement of infected cells (cytomegaly)
• Examples:
• Human cytomegalovirus (CMV / HHV-5) → congenital infections, opportunistic disease in immunocompromised
• Human herpesvirus 6 (HHV-6) → roseola infantum
• Human herpesvirus 7 (HHV-7) → also linked to roseola-like illness

3. Gamma-herpesviruses (γ-herpesvirinae)

• Characteristics:
• Latency in B-lymphocytes
• Associated with tumors (oncogenic potential)
• Examples:
• Epstein-Barr virus (EBV / HHV-4) → infectious mononucleosis, Burkitt’s lymphoma, nasopharyngeal carcinoma
• Kaposi’s sarcoma-associated herpesvirus (KSHV / HHV-8) → Kaposi’s sarcoma, primary effusion lymphoma

Herpes Simplex Virus (HSV)

HSV belongs to the alpha herpesvirus group. HSV are of two types, HSV-1 and HSV-2, with very similar characteristics. The overall sequence homology between HSV-1 and HSV-2 is about 50%. HSV-1 has tropism for oral epithelium, while HSV-2 has tropism for genital epithelium. HSV-1: primarily causes oral herpes, and is generally responsible for cold sores and fever blisters around the mouth and on the face. HSV-2: primarily causes genital herpes, and is generally responsible for genital herpes outbreaks.

HSV-1 (Herpes Simplex Virus Type 1): Primarily causes oral herpes, including cold sores or fever blisters around the mouth. It can also cause genital herpes through oral-genital contact.

HSV-2 (Herpes Simplex Virus Type 2): Primarily causes genital herpes, leading to sores or blisters in the genital and anal areas.

 Morphology 

Family: Herpesviridae

• Structure:
• Genome: Double-stranded DNA (linear).
• Capsid: Icosahedral symmetry, composed of 162 capsomeres.
• Tegument: Protein layer between the capsid and envelope, aiding in virus replication.
• Envelope: Lipid bilayer derived from host cells, studded with glycoproteins (e.g., gB, gC, gD, and gE) important for attachment and immune evasion.
• Size: 120-200 nm in diameter.

Replication of Herpes

Attachment and Entry-

The replication of Herpes Simplex Virus begins when the viral glycoproteins present on its envelope, such as gB, gC, gD, and gH/gL, interact with specific receptors on the host cell surface, including heparan sulfate and nectin-1. 

Penetration

After attachment, the viral envelope fuses with the cell membrane, and the viral capsid (protein shell) carrying the DNA enters the cytoplasm.

Transport to the Nucleus

Once inside the cell, the viral capsid does not stay in the cytoplasm. It moves along tiny cellular “tracks” (microtubules) until it reaches the nucleus. At the nuclear pore, the capsid releases the viral DNA into the nucleus, where further steps of replication will take place.

Biosynthesis

In the nucleus, the viral DNA becomes circular and begins making viral proteins in a stepwise manner. First, immediate early proteins are produced, which regulate viral activity. Then, early proteins are made, which include enzymes needed for copying the DNA, making more DNA. Finally, late proteins are produced, which are mainly structural proteins, the Capsid that will form the new virus particles

Assembly

The newly made DNA is inserted into empty protein shells (capsids) inside the nucleus. This process forms immature virus particles that still need their final outer covering (envelope).

Maturation and Release

The capsids move out of the nucleus and pick up their envelope by budding through membranes in the cell that contain viral glycoproteins. These mature viruses are then carried to the cell surface and released by exocytosis, or sometimes by breaking open the cell.

Latency

Unlike many viruses that immediately destroy host cells, HSV has a special feature: it can remain hidden in nerve cells without causing active infection. In this latent state, the viral DNA stays in the nucleus but only produces a few special RNA molecules called latency-associated transcripts (LATs). No new viruses are formed during latency. Later, under stress, fever, or weakened immunity, the virus can “wake up” and start a new cycle of replication, causing recurrent infection.

Pathogenesis of Herpes

• Entry → virus enters via mucosa/skin.
• Local replication → vesicles and ulcers form.
• Neural spread & latency → virus establishes latency in sensory ganglia.
• Reactivation → virus returns to skin/mucosa causing recurrent lesions.
• Severe disease → in immunocompromised, can cause encephalitis, keratitis, or disseminated infection.

Herpes Simplex Virus (HSV) usually enters the body through mucous membranes (such as the mouth, eyes, or genitals) or broken skin. At the site of entry, the virus infects epithelial cells, where it multiplies and causes local cell damage. This leads to the formation of painful blisters or ulcers, which are the typical lesions of herpes infection.

After primary infection, HSV spreads to nearby sensory nerve endings and travels along the nerves to reach the nerve cell bodies in ganglia (trigeminal ganglion for HSV-1 and sacral ganglion for HSV-2). Here, the virus becomes latent and remains hidden inside the neurons for the lifetime of the host. During latency, no infectious particles are produced, but the viral DNA stays inside the nucleus of neurons.

Reactivation can occur when the immune system is weakened or due to triggers like stress, fever, or sunlight. When reactivated, the virus travels back along the nerve fibers to the skin or mucosa, causing recurrent lesions at or near the original site of infection. These recurrent infections are usually milder than the primary infection but are an important feature of HSV pathogenesis.

In immunocompromised individuals, HSV can cause more severe disease, including encephalitis, keratitis (eye infection leading to blindness), or widespread skin infections.

Transmission

Herpes spreads through direct contact with an infected person, even if they are asymptomatic. Common ways of transmission include:

• HSV-1:
• Saliva (kissing, sharing utensils, or towels).
• Oral-genital contact.
• HSV-2:
• Sexual contact (vaginal, anal, or oral).
• Skin-to-skin contact in the genital area.

Both types of HSV can remain dormant in the body and reactivate under certain conditions.

2. Symptoms

Oral Herpes (HSV-1):

• Blisters or cold sores around the mouth and lips.
• Tingling, itching, or burning sensations before blisters appear.
• Fever, sore throat, or swollen lymph nodes (especially in first-time infections).

Genital Herpes (HSV-2):

• Painful blisters or sores in the genital or anal area.
• Itching or tingling in the affected area.
• Pain during urination.
• Flu-like symptoms (fever, body aches) during initial outbreaks.

Asymptomatic Cases:

• Many people with HSV do not experience noticeable symptoms but can still transmit the virus.

Laboratory Diagnosis

Specimen collection

• The best specimens are fluid from vesicles, swabs from ulcers, throat or genital swabs, cerebrospinal fluid (in suspected encephalitis), and corneal scrapings (for keratitis).

• Ø  Tzanck smear → multinucleated giant cells.
• Ø  Culture → cytopathic effect.
• Ø  Antigen detection → immunofluorescence/ELISA.
• Ø  PCR → most sensitive, especially for encephalitis.
• Ø  Serology → IgM (recent), IgG (past infection).

1. Direct Microscopy
• Tzanck smear: A smear is made from the base of a vesicle, stained, and examined under the microscope. The presence of multinucleated giant cells suggests HSV infection, but this test is not very specific.

2. Antigen Detection
• Viral antigens can be detected directly from lesion samples using immunofluorescence or ELISA. This method is faster than culture.

3. Virus Isolation (Culture)
• The specimen is inoculated into cell cultures (e.g., Vero cells) . HSV produces a characteristic cytopathic effect (CPE): cells become rounded, enlarged, and form multinucleated giant cells. Culture is considered a reliable diagnostic method but takes time.

4. Molecular Methods
• PCR (Polymerase Chain Reaction) is the most sensitive and specific test. It is especially important for detecting HSV in encephalitis or cases with low viral load.

5. Serology
• Blood tests can detect HSV antibodies (IgM and IgG). IgM indicates recent infection, while IgG shows past exposure. Serology is not very useful for routine diagnosis but may help in epidemiological studies.

 Prevention and Control

A. Prevention

1. Personal Hygiene:
• Avoid direct contact with active lesions.
• Avoid sharing personal items like razors or towels.
2. Safe Sexual Practices:
• Use condoms during sexual activity.
• Avoid sexual contact during outbreaks.
3. Vaccination:
• Currently under development; no licensed HSV vaccine available.
4. Neonatal Prevention:
• Cesarean delivery in pregnant women with active genital herpes to prevent neonatal transmission.

B. Control

1. Antiviral Medications:
• Acyclovir, valacyclovir, and famciclovir reduce symptoms, duration, and viral shedding.
• Prophylactic antivirals for frequent recurrences.
2. Public Health Measures:
• Education about HSV transmission and symptoms.
• Screening high-risk individuals (e.g., pregnant women).

C. Special Considerations

• Immunocompromised Patients:
• Aggressive antiviral therapy is required.
• Prevention of secondary infections.
• Neonatal Herpes:
• Immediate antiviral therapy (intravenous acyclovir).