Contact Diseases (9)

contact diseases (overview)

• direct contact transmission: person-to-person

  • sexual dz = STDs (STIs)

  • non-sexual dz = non-STDs

• indirect contact transmission: person-to-fomite

non-STDs

• trachoma (bacterial)

• hepatitis C (viral) (by contaminated blood → not an STD)

STDs

bacterial

• gonorrhea

• genital chlamydia

• syphilis

protist

• trichomoniasis

viral

• genital herpes

• hepatitis B

• HIV/AIDs

chlamydial (Chlamydia trachomatis) infections

• cause dz called “Chlamydia” (bacterial infections)

• serotype determines type of dz:

1. non-sexual = dz of eye (trachoma)

2. sexual = dz of genital tract (genital chlamydia, cervicitis, pelvic inflammatory dz (PID) → infertility)

• VF: replicates in epithelial cells of reproductive tract (obligate intracellular parasite)

• MOT: contact (STD & non-STDs), arthropodborne (ex. sandflies; non-STDs)

trachoma

• cause: Chlamydia trachomatis serotype, gram — coccobacillus, obligate intracellular parasite

• VF: 2 forms (life cycle)

  • elementary bodies: infectious, invades epithelial cells

  • reticulate bodies: non-infectious, intracellular, replicates

• reservoir: humans

• MOT:

  • (direct) hand-to-eye contact w/ eye discharge

  • (indirect) shared objects (fomites)

  • (arthropod) sand flies carrying eye discharge

• sxs: conjuctivitis of upper eye lid → scarring/contracting of conjunctiva → eyelashes turn inward → eyelashes scratch cornea → corneal cloudiness → permanent blindness

• PF: unsanitary conditions, overcrowding, children

• dx: based on sxs (vision)

• prevention: wash hands, sand fly control, no vaccine

• tx: abx, surgery

• misc: portal of entry = mucous membranes (conjunctiva), leading preventable cause of blindness worldwide, most in Africa (children < 5 yo greater than 60%)

gonorrhea

• cause: Neisseria gonorrhoeae, gram — diplococcus (coffee bean-shaped)

• VF: capsule, fimbriae, opa proteins (bind T-cell receptors → inhibit immune response)

• reservoir: humans

• MOT: sexual contact

• sxs: urethritis (gonococcal urethritis)

  • men: painful urination, yellow discharge, epididymitis

  • women: fewer sxs, pelvic inflammatory disease (PID)

  • if untreated: (systemic) endocarditis, meningitis, arthritis

  • neonatal complication: ophthalmia neonatorum (blindness after vaginal birth)

• dx: urine test, oral/urethral/rectal swab, PCR, culture (gonococci)

• prevention: education, safe sex practices

• tx: abx (injection, oral)

• misc: ↑ teens/YA, coinfection w/ genital chlamydia (tx both @ same time)

genital chlamydia

• cause: Chlamydia trachomatis serotype, gram — coccobacillus, obligate intracellular parasite

• VF: 2 forms → elementary body, reticulate body

• reservoir: humans

• MOT: sexual contact through epithelial mucosa

• sxs: non-gonococcal urethritis (NGU)

  • men: mostly sxs, painful urination, clear/watery discharge

  • women: mostly asxs, pelvic inflammatory disease (PID)

• dx: NAATs (nucleic acid amplification tests)

  • PCR (type of NAAT), use vaginal/urethral swabs or urine

• prevention: education, safe sex practices

• tx: abx

• misc: can cause ophthalmia neonatorum, coinfection w/ gonorrhea, most common bacterial STD in US

syphilis

• cause: Treponema pallidum, gram — spirochete (spiral), motile

• VF: lipid outer layer → weak immune response

• reservoir: humans

• MOT: sexual contact

• sxs:

  • stage 1: chancre (painless sore) 3 weeks after exposure, highly infectious, disappears after 2 weeks

  • stage 2: skin & mucosal rash, palms/soles, can lead to → latent stage (no sxs for decades)

  • stage 3: appears decades after latency, gummas (soft, tumor-like lesions on many organs → bone, brain, heart, skin), arthritis

    • CV syphilis, neurosyphilis (dementia)

• dx: serology, direct detection (T. pallidum), indirect detection (Abs)

• prevention: education, safe sex practices

• tx: abx (effective only early stages)

• misc: congenital syphilis (developmental damage to fetus, stillbirths)

trichomoniasis (trich)

• cause: Trichomonas vaginalis, kingdom protista, protozoan parasite, motile (flagella, undulating membrane), pear-shaped

• VF: axostyle (structure w/ sharp point that anchors to epithelial cells)

• MOT: sexual contact

• reservoir: men

• sxs:

  • men: usually asxs carriers (in urine & semen), some urethral discharge, painful urination

  • women: sxs, frothy greenish-yellow discharge, foul odor, painful urination

• dx: sxs, microscopic observation of live protozoa from swab

• prevention: education, safe sex practices

• tx: antiparasitic/antiprotozoal

• misc: ↓ birth weight/premature birth risk, >1 mil/year in US, most common non-viral STD in US

genital herpes

• cause: HSV-2 (HHV-2), herpesviridae family, enveloped, DNA virus

• VF: latent viral infection → hide in NS

• reservoir: humans

• MOT: sexual contact

• sxs: painful fluid-filled vesicles on genitals, painful urination, heal w/n 2 weeks (not cured)

  • “outbreaks” of vesicles: primary episodes → recurrent episodes

• dx: culture, PCR

• prevention: education, safe sex practices

• tx: management/suppression only w/ antivirals (-vir)

• misc: 1 in 4 adults over age 30 infected in US (2nd most common STD)

neonatal herpes

• cause: herpesvirus crosses placenta

• sxs: CNS damage, developmental delays, blindness, hearing loss

• survival: 40%

• MOT: during delivery

hepatitis B

• cause: hepatitis B virus, enveloped DNA virus

• MOT: sexual contact, accidental needle sticks

• sxs:

  • acute: fever, N/V, ↓ appetite, jaundice

  • chronic: liver failure, cirrhosis, liver cancer

• dx: blood tests (IgM), liver ultrasound, liver biopsy

• prevention: vaccine, education, safe sex

• tx: no cure, antivirals (Tenofovir), interferon injections, liver transplant

• misc: 10% become chronic

hepatitis C

• cause: hepatitis C virus, enveloped RNA virus

• MOT: contaminated blood, blood transfusions, tattoos, IV drug use

• sxs: asxs initially

  • chronic: liver failure, cirrhosis, liver cancer

• dx: blood tests (IgM), liver ultrasound, liver biopsy

• prevention: no vaccine, universal blood precautions

• tx: no cure, daily antivirals (2-6 mo), liver transplant

• misc: 85% become chronic, new antivirals can “cure” up to 95%, drugs = expensive

HIV/AIDS

• cause: human immunodeficiency virus (HIV), retroviridae, enveloped RNA virus

  • strains: HIV-1, HIV-2

• VF: gp120 spikes

• target cells: CD4+ T cells

• MOT: sexual contact

  • secondary: shared IV needles, breast milk, transplacental, blood transfusion, organ transplant

• viral replication:

  • reverse transcriptase: RNA → DNA

  • integrase inserts DNA into host DNA

  • active infection → lytic cycle

  • latent infection → provirus (lysogenic cycle)

HIV phases (sxs)

phase 1

• asymptomatic or lymphadenopathy

• seroconversion

phase 2

• CD4 cells decline

• persistent candida & diarrhea

• fever

phase 3 (clinical AIDS)

• opportunistic infections

• Kaposi’s sarcoma

• atypical pneumonia

• miliary TB

• CD4 count <200 cells/µL

HIV diagnosis & prevention

• dx: (tests) ELISA, plasma viral load (PVL), rapid tests, self-testing kits

• prevention: no vaccine, education, safe sex, PrEP (Truvada)

HIV treatment

• tx: no cure, antiretroviral therapy (ART)

  • goal: undetectable plasma viral load

• drug classes:

  • HAART

  • fusion/cell entry inhibitors

  • reverse transcriptase inhibitors (NRTIs & NNRTIs)

  • integrase inhibitors

  • protease inhibitors

human herpes virus (HHV)

• HHV-1: cold sores

• HHV-2: genital herpes

• HHV-3: chicken pox

• HHV-8: HIV cancer → Kaposi sarcoma