Microbiology Study Notes: Hepatitis C, Neisseria gonorrhoeae, and Treponema pallidum (Syphilis)

Chapter 25.4: Hepatitis C

Overview of Hepatitis C Virus (HCV)

Hepatitis C is a viral infection caused by the flavivirus known as HCV. It primarily affects the liver and is a major cause of chronic liver disease worldwide.

• Transmission: Acquired through blood contact, including blood transfusions and needle sharing among drug abusers.

• Infection Characteristics: Infections can vary in severity; chronic liver disease is more common than acute cases.

• Complications: Chronic HCV infection can lead to liver cancer (hepatocellular carcinoma).

• Treatment: Interferon and ribavirin are used to lessen liver damage, but there is no definitive cure.

• Prevention: No vaccine is currently available for HCV.

Example: A patient with a history of intravenous drug use presents with elevated liver enzymes and is diagnosed with chronic hepatitis C.

Chapter 18.3: Neisseria gonorrhoeae (The Gonococcus)

General Characteristics and Transmission

Neisseria gonorrhoeae is a Gram-negative diplococcus responsible for the sexually transmitted disease gonorrhea. Transmission occurs via direct contact, typically sexual.

• Strictly Human Infection: The bacterium only infects humans and is among the top five most common STDs.

• Survival Outside Host: Does not survive more than 1-2 hours on fomites.

Pathogenicity Factors

• Fimbriae and Surface Molecules: Aid in attachment to host cells and slow phagocytosis by immune cells.

• IgA Protease: Cleaves secretory IgA, helping the bacterium evade mucosal immunity.

Clinical Manifestations

Genital Gonorrhea in Males

• Symptoms: Urethritis, yellowish discharge, scarring, and potential infertility.

• Asymptomatic Cases: Approximately 10% of males may not show symptoms.

Genitourinary Gonorrhea in Females

• Symptoms: Vaginitis, urethritis, and salpingitis (pelvic inflammatory disease, PID), often leading to mixed anaerobic abdominal infection.

• Complications: Common cause of sterility and ectopic tubal pregnancies.

• Asymptomatic Cases: About 50% of females may be asymptomatic.

Gonococcal Infections in Children

• Transmission: Infants can be infected during passage through the birth canal of infected mothers.

• Symptoms: Eye inflammation (ophthalmia neonatorum), blindness, and possible infection of the pharynx and respiratory tract.

• Prevention: Prophylactic treatment with erythromycin immediately after birth.

Diagnosis and Control

• Microscopy: Gram stain reveals Gram-negative intracellular (within neutrophils) diplococci from urethral, vaginal, cervical, or eye exudate.

• Identification: Presumptive identification based on microscopy; recurrent infections can occur.

Chapter 21.1: Treponema pallidum (Syphilis)

General Characteristics

Treponema pallidum is a spirochete bacterium that causes syphilis. It is highly fastidious and sensitive, unable to survive long outside the host. Transmission is sexual or transplacental (from mother to fetus).

• Habitat: Found in oral cavity, intestinal tract, and perigenital regions of humans and animals.

• Congenital Syphilis: Can cross the placenta at any trimester, causing fetal infection.

Stages of Syphilis

• Primary Syphilis: T. pallidum multiplies at the site of entry, forming a lesion called a chancre (commonly mouth or genitals). Fluid from the chancre is highly contagious. The chancre heals as the spirochete enters the bloodstream.

• Secondary Syphilis: Spirochete multiplies in the bloodstream, causing a generalized skin rash (palms, soles), fever, headache, and sore throat. The rash is non-pruritic and can persist for months before disappearing spontaneously.

• Latency and Tertiary Syphilis: About 30% of untreated cases enter a latent period (up to 20 years). Tertiary syphilis involves damage to multiple organs (heart, skin, bones) and may result in gummas (painful swollen tumors).

Congenital Syphilis

• Transmission: T. pallidum passes through the placenta, inhibiting fetal growth and causing miscarriage or stillbirth.

• Symptoms in Infants: Nasal discharge, skin eruptions, bone deformation, and nervous system abnormalities.

Diagnosis and Testing

• Clinical Assessment: Consider symptoms and medical history.

• Microscopy: Staining techniques to visualize spirochetes.

• Serological Tests: Detect antibodies against T. pallidum (RPR, VDRL, FTA-ABS).

Treatment

• First-line: Single dose of penicillin G.

• Alternatives: Tetracycline and doxycycline for penicillin-allergic patients.

Summary Table: Key Features of Three Pathogens

Pathogen	Disease	Transmission	Main Symptoms	Diagnosis	Treatment
Hepatitis C Virus	Hepatitis C	Blood contact	Chronic liver disease, risk of cancer	Serology, liver function tests	Interferon, ribavirin (no cure)
Neisseria gonorrhoeae	Gonorrhea	Direct contact (sexual)	Urethritis, discharge, PID, eye infection in neonates	Gram stain, culture	Antibiotics (e.g., ceftriaxone)
Treponema pallidum	Syphilis	Sexual, transplacental	Chancre, rash, gummas, congenital defects	Microscopy, serology (RPR, VDRL, FTA-ABS)	Penicillin G, tetracycline, doxycycline

Additional info: These notes expand on the original points with definitions, clinical context, and a summary table for comparison. All three pathogens are significant in medical microbiology due to their public health impact and diagnostic challenges.