Infectious Teratogens (TORCH+)

Infectious teratogens cause structural and neurodevelopmental anomalies through several mechanisms: direct cytopathic effect on developing tissues, inflammatory disruption of organogenesis, and persistent infection of the fetal CNS leading to progressive injury postnatally. TORCH is the historical mnemonic (Toxoplasmosis, Other, Rubella, Cytomegalovirus, Herpes simplex), but several "Other" agents (parvovirus B19, syphilis, varicella, Zika) are now important enough to deserve separate mention. The acronym TORCH+ captures the modern list.

The diagnostic challenge: many TORCH infections share a phenotypic core (chorioretinitis, microcephaly, hepatosplenomegaly, intracranial calcifications) but differ in the specific pattern of these findings; that pattern is the clinical discriminator that lands the diagnosis.

• Organism: Toxoplasma gondii (protozoan).
• Maternal exposure: undercooked meat, cat-feces contact, contaminated soil/water. Most maternal infections are asymptomatic or flu-like.
• Transmission: increases with gestational age (~10–15% in 1st trimester, ~60–70% in 3rd). Severity is inverse: 1st-trimester transmission is rarer but more devastating.
• Classic triad:
  • Chorioretinitis (most common finding overall; may present at birth or years later)
  • Hydrocephalus
  • Diffuse intracranial calcifications
• Other findings: microcephaly, seizures, intellectual disability, sensorineural hearing loss, anemia.
• Distinguishing feature: diffuse (not periventricular) intracranial calcifications.
• Diagnosis: maternal serology (IgM/IgG, avidity testing); fetal PCR on amniotic fluid.
• Treatment: spiramycin during pregnancy if maternal infection identified; pyrimethamine + sulfadiazine + leucovorin postnatally for confirmed congenital infection.
• Prevention: avoid undercooked meat, hand hygiene with cat litter, no soil contact without gloves.

Congenital Syphilis

• Organism: Treponema pallidum.
• Early findings (within first 2 years): maculopapular rash, snuffles (bloody nasal discharge), hepatosplenomegaly, pseudoparalysis of Parrot, periostitis, jaundice, lymphadenopathy.
• Late findings (after 2 years):
  • Hutchinson teeth (notched permanent incisors)
  • Mulberry molars
  • Saddle nose
  • Saber shins (anterior tibial bowing)
  • Interstitial keratitis
  • Sensorineural deafness (CN VIII)
  • The triad Hutchinson teeth + interstitial keratitis + deafness = Hutchinson triad.
• Diagnosis: nontreponemal (RPR/VDRL) + treponemal tests; CSF VDRL if neurosyphilis suspected.
• Treatment: penicillin G, the only adequate treatment in pregnancy. Alternative regimens fail to treat the fetus.
• Surge in resurgence: congenital syphilis rates rising in the US since 2013, paralleling adult primary/secondary syphilis trends.

Parvovirus B19

• Mechanism: tropism for erythroid precursors (P-antigen receptor) → fetal anemia → high-output cardiac failure → hydrops fetalis.
• Maternal exposure: erythema infectiosum (fifth disease) outbreaks among children; occupational exposure (school, daycare).
• Risk window: fetal loss highest at 13–20 weeks; minimal risk after 20 weeks. Overall fetal loss ~5–10%; hydrops in 3–5% of infected.
• Diagnosis: maternal IgM/IgG; if maternal infection confirmed, serial fetal ultrasound for hydrops with MCA-PSV Doppler to detect anemia.
• Management: intrauterine fetal transfusion can reverse hydrops. No vaccine; no specific antiviral.
• Distinguishing feature: hydrops without structural malformation. Parvo doesn't cause classic dysmorphism; the injury is hematologic.

Varicella (Chickenpox)

• Organism: varicella-zoster virus (VZV).
• Congenital varicella syndrome, when maternal infection occurs at 8–20 weeks gestation:
  • Cicatricial skin scars (in dermatomal distribution)
  • Limb hypoplasia
  • Microcephaly, cortical atrophy
  • Chorioretinitis, cataracts
  • Cognitive impairment
• Neonatal varicella, when maternal infection within 5 days before to 2 days after delivery: severe disseminated infection in newborn, ~30% mortality without VZIG.
• Vaccine is live-attenuated → contraindicated in pregnancy; vaccinate susceptible women preconceptionally.

Zika Virus

• Vector: Aedes mosquitoes; sexual transmission also reported.
• Major findings: severe microcephaly, intracranial calcifications (subcortical/cortical pattern), ventriculomegaly, brain stem and cerebellar hypoplasia, ocular abnormalities (chorioretinal atrophy, optic nerve abnormalities), arthrogryposis.
• "Congenital Zika syndrome" is now recognized as a defined teratogenic phenotype.
• Risk: highest with first-trimester exposure but documented across pregnancy.
• Prevention: avoid travel to endemic areas; barrier protection if partner exposed.

• Organism: rubella virus.
• Critical window: first 12 weeks gestation (highest risk in first 8 weeks; minimal after 20 weeks).
• Congenital rubella syndrome (CRS) classic triad:
  • Sensorineural deafness (most common single defect)
  • Cardiac defects, most often patent ductus arteriosus and peripheral pulmonary artery stenosis
  • Cataracts ("salt and pepper" chorioretinopathy is also common)
• Other findings: microcephaly, intellectual disability, "blueberry muffin" rash (extramedullary hematopoiesis), hepatosplenomegaly, late-onset diabetes mellitus.
• Vaccine is live-attenuated → contraindicated in pregnancy. CRS is now rare in vaccinated populations; pre-conception screening (rubella IgG) is standard.

• Organism: human cytomegalovirus (HHV-5).
• The most common congenital infection in the developed world (~0.5–1% of live births).
• Most infections are asymptomatic at birth. ~10% are symptomatic; ~10–15% of asymptomatic newborns develop late sequelae (especially sensorineural hearing loss).
• Symptomatic congenital CMV:
  • Periventricular calcifications (this is the classic discriminator from toxoplasmosis, which has diffuse calcifications)
  • Sensorineural hearing loss (most common cause of non-genetic SNHL)
  • Microcephaly
  • Chorioretinitis
  • Hepatosplenomegaly, jaundice, petechiae ("blueberry muffin" rash)
  • Intellectual disability
• Diagnosis: PCR of urine or saliva within 21 days of life. Newborn dried-blood-spot testing increasingly used for retrospective diagnosis when SNHL detected later.
• Treatment: oral valganciclovir × 6 months for symptomatic newborns reduces hearing-loss progression.

• Organism: HSV-1 or HSV-2.
• Congenital (intrauterine) HSV is rare; most neonatal HSV is acquired during passage through an infected birth canal.
• Intrauterine HSV: skin vesicles/scarring, chorioretinitis, microcephaly, intracranial calcifications.
• Neonatal HSV (perinatally acquired): three patterns (skin/eye/mouth [SEM], CNS, disseminated). CNS and disseminated forms are devastating.
• Risk highest with primary maternal infection at delivery; lower with recurrent. C-section indicated for active genital lesions at delivery.
• Treatment: acyclovir IV × 14 days (SEM) or 21 days (CNS/disseminated).