Helicobacter pylori

Characteristics and Clinical Significance

Helicobacter pylori is a Gram-negative, highly motile, spiral-shaped bacterium with multiple polar flagella. It is a major human pathogen associated with gastrointestinal diseases.

• Gram-negative, spiral-shaped, highly motile due to multiple polar flagella

• Produces urease, an enzyme that hydrolyzes urea to ammonia, neutralizing stomach acid

• Causes approximately 80% of stomach and duodenal ulcers; acts as a cofactor in stomach cancer

• Individuals with type O blood have a 1.5–2 times higher rate of ulcers

Transmission and Pathogenesis

• Transmitted person-to-person via oral-oral or oral-fecal routes

• Tends to cause chronic infections unless treated with antibiotics

• Chronic gastritis may progress to gastric cancer

Diagnosis and Treatment

• Clinical signs: belching, stomach pain

• Urease test: patient ingests 13C or 14C-labeled urea; presence of labeled CO2 in exhaled breath indicates urease activity

• Definitive diagnosis: recovery of organisms or observation from biopsy; stool antigen tests

• Treatment: combination of antibiotics

• Discovery: Robin Warren and Barry Marshall (Nobel Prize, 2005) for linking H. pylori to peptic ulcers

Hepatitis Viruses

Overview and Classification

Hepatitis refers to inflammation of the liver, commonly caused by several distinct viruses. These viruses differ in their genetic material, transmission, and clinical outcomes.

• DNA virus: Hepatitis B virus (HBV)

• RNA viruses: Hepatitis A virus (HAV), Hepatitis C virus (HCV), Hepatitis E virus (HEV), Hepatitis D virus (HDV; defective, requires HBV)

Major Hepatitis Viruses Comparison

Hepatitis A Virus (HAV)

• Fecal-oral transmission; multiplies in small intestine, enters blood, carried to liver

• Most infections are subclinical or mild; jaundice is rare

• No specific treatment after symptoms begin

• Prevention: inactivated/attenuated vaccines; immune globulin for travelers

Hepatitis B Virus (HBV)

• Transmitted via blood, sexual contact, perinatal

• Chronic infection can lead to cirrhosis and liver cancer

• Pathogenesis: virus enters via skin/mucosa or injection, multiplies in liver, releases into blood; incubation ~7 weeks

• Diagnosis: serological tests (ELISA), screening of blood/organs/semen

• Treatment: interferon for chronic cases; supportive care for mild cases

• Prevention: passive immunization (antibodies), vaccination for high-risk groups and newborns

Hepatitis C Virus (HCV)

• Caused by a flavivirus; transmitted via blood (transfusions, needle sharing)

• Often leads to chronic liver disease and cancer

• Treatment: interferon and ribavirin (no cure)

• No vaccine available

Neisseria gonorrhoeae: The Gonococcus

Pathogenicity and Transmission

Neisseria gonorrhoeae is a Gram-negative diplococcus responsible for gonorrhea, a common sexually transmitted disease (STD).

• Transmission: direct contact (sexual)

• Fimbriae and surface molecules aid attachment and slow phagocytosis

• IgA protease cleaves secretory IgA, aiding immune evasion

• Strictly human infection; does not survive long on fomites

Clinical Manifestations

• Male: Urethritis, yellowish discharge, scarring, infertility; ~10% asymptomatic

• Female: Vaginitis, urethritis, salpingitis (PID), sterility, ectopic pregnancies; 50% asymptomatic

• Children: Eye inflammation, blindness, pharynx/respiratory tract infection; prevented by erythromycin prophylaxis at birth

Diagnosis and Control

• Gram stain: Gram-negative intracellular diplococci in neutrophils from exudate

• Presumptive identification; recurrent infections possible

Treponema pallidum and Syphilis

Characteristics and Transmission

Treponema pallidum is a spirochete bacterium causing syphilis, transmitted sexually and transplacentally.

• Extremely fastidious; cannot survive long outside host

• Transmitted sexually and from mother to fetus (congenital syphilis)

Stages of Syphilis

• Primary: Chancre formation, highly contagious fluid, heals as spirochete enters blood

• Secondary: Rash (skin, palms, soles), fever, headache, sore throat; rash persists for months

• Latency/Tertiary: ~30% enter latent period; tertiary syphilis causes organ damage, gummas

• Congenital syphilis: transplacental transmission, fetal growth inhibition, miscarriage, stillbirth, symptoms in infants (nasal discharge, skin eruptions, bone/nervous system abnormalities)

Diagnosis and Treatment

• Diagnosis: symptoms, history, microscopy, serological tests (RPR, VDRL, FTA-ABS)

• Treatment: single dose penicillin G; tetracycline/doxycycline for penicillin allergy

Chlamydia trachomatis

Characteristics and Strains

Chlamydia trachomatis is an obligate intracellular bacterium with a human reservoir. Two main strains infect humans:

• Trachoma strain: attacks mucous membranes of eyes, genitourinary tract, lungs

• Lymphogranuloma venereum (LGV) strain: invades lymphatic tissues of genitalia

Chlamydial Diseases

• Ocular trachoma: severe infection, deforms eyelid/cornea, may cause blindness

• Inclusion conjunctivitis: occurs in newborns passing through birth canal; prevented by erythromycin/doxycycline

• Chlamydiosis: most prevalent STD; long-term reproductive damage; asymptomatic in 70% women, 10% men

• Nongonococcal urethritis (NGU): inflammation of urethra in males, mimics gonorrhea

• Pelvic inflammatory disease (PID): in women

• Lymphogranuloma venereum: disfiguring disease of external genitalia and pelvic lymphatics

Identification and Treatment

• Sampling: dislodge cells from mucosal surface

• Immunofluorescence and PCR-based tests

• Giemsa/iodine stains for inclusion conjunctivitis

• Not recommended for urogenital specimens due to low sensitivity

• Treatment: doxycycline and azithromycin

Herpes Simplex Viruses (HSV)

Characteristics and Types

Herpes simplex viruses are enveloped DNA viruses infecting humans in two main forms:

• HSV-1: cold sores, fever blisters (early childhood)

• HSV-2: genital lesions, possibly oral (ages 14–29)

• Can be spread without visible lesions

Epidemiology and Clinical Features

• Transmission: direct contact with secretions; active lesions are most infectious

• Genital herpes can be transmitted in absence of lesions

• Recurrent infections are common

Herpes of the Newborn

• HSV-1 and HSV-2 infections can be fatal in neonates/fetuses

• Transmission: before/during birth, hand transmission by mother

• Infection of mouth, skin, eyes, CNS

• Prevention: screening pregnant women, C-section if outbreak at birth

Diagnosis, Treatment, and Control

• Diagnosis: vesicles/exudate, giant cells in lesion scrapings, culture, direct fluorescent antibody tests

• Treatment: acyclovir, famciclovir, valacyclovir, topical medications

Human Papillomavirus (HPV)

Characteristics and Transmission

HPV is a non-enveloped double-stranded DNA virus causing warts (papillomas) and is associated with reproductive cancers.

• Over 100 strains; 14 types increase risk for reproductive cancer

• Transmitted via direct contact or contaminated fomites; incubation 2 weeks to over a year

• Most warts regress over time; can be removed

Clinical Significance and Prevention

• Early detection: inspection of genitals, Pap smear for abnormal cervical cells

• Approved vaccine: Gardasil 9