Toxoplasmosis

Background/Epidemiology

• Caused by Toxoplasma gondii (protozoa)
  • Incubation period: 7-14 days
  • Transmitted via Ingestion (oral); blood contact.  Most commonly transmitted via cats, in whom the full life cycle of toxoplasma can occur
• One of the TORCH infections
  • High risk of transmission to foetus from mother, particularly during the third trimester (up to 60%)
  • Can cause foetal abnormalities (see below) if caught in the first/early second trimester
  • Important to treat any mothers
• High seroprevalence (16-40%)
  • NB this does not necessarily reflect true prevalence as IgG levels may be raised with old infections.  In any case, the prevalence is still high.

Presentation

• Adults- immunocompetent
  • Most (90%) are asymptomatic and the remainder usually present with vague symptoms e.g. lethargy/mild fever, lymphadenopathy
• Newborns (congenitally acquired)
  • Depends on the duration (i.e. the gestational age at which infection started)
    • If early- can cause abnormalities such as microcephaly; foetalis hydrops; hydrocephalus; even stillbirth
    • If later, can rarely cause retinochoroidosis; developmental delay/epilepsy; prematurity/IUGR; hydrocephalus
      • Usually, neonatal infection is asymptomatic
• Can cause life-threatening infections in immunocompromised hosts (usually a pneumonitis with multi-organ involvement/failure)

Investigations

• Serology
  • IgG
    • NB this persists for life.  A patient (e.g. mother) with no toxoplasma IgG indicates risk of new acquired infection
    • Can indicate current or previous infection- IgG avidity can help to distinguish between the two
• PCR can be used to detect active infection
• Imaging (foetal/neonatal brain USS) can be helpful but is rarely specific for toxoplasmosis.  Changes include hydrocephalus/ventriculomegaly; CNS calcifications

Management

• For immunocompetent patients (non-pregnant)- no treatment is usually required
• For immunocompromised patients
  • Pyrimethamine/sulfadiazine and folinic acid is standard (other combination regimes are available) for 4-6 weeks
• For newly acquired maternal infection
  • avoid pyrimethamine in the 1st trimester- otherwise use the above regime if the foetus is known to be infected
  • use spiramycin ASAP if the foetus is not infected (or status unknown)

NB The UK does not routinely screen pregnant women for toxoplasmosis (unless immunocompromised).  

Infection risk can be reduces by good hand hygiene and other infection control measures.