CNS Infections: Protozoa

Snapshot

• A 56-year-old nurse is brought to the emergency room for altered mental status. She spent a year in West Africa volunteering at a hospital. She returned to the US about 4 weeks ago. At that time, she had intermittent fevers with general malaise and a transient urticarial rash and noted a bug bite on her right forearm. She was then treated for malaria, though diagnostic testing was equivocal. In the past week, she became increasingly somnolent during the day. She also lost 15 lbs within the past 2 weeks. A lumbar puncture is done and diagnostic studies are sent. Meanwhile, she is started on empiric therapy. (African sleeping syndrome caused by Trypanosoma brucei)

Introduction

• Protozoa
• single-celled eukaryotes, often parasitic, that feed on organic tissues

Toxoplasma gondii

• Introduction
  • clinical syndrome
    • toxoplasmosis
  • reservoirs
    • domestic cats
  • transmission
    • ingestion of cysts in meat
    • ingestion of food contaminated with oocysts from cat excretion
    • can be transmitted via placenta to neonate 
      • congenital toxoplasmosis 
        • triad of chorioretinitis, hydrocephalus, and intracranial calcifications 
  • pathogenesis
    • tachyzoites are rapidly reproductive and invasive
    • cysts are slow-dividing and latent, arising 1 week after infection 
      • can remain in hosts for a lifetime in the CNS
    • oocysts contain sporozoites, can spread them to other hosts, and can survive in the environment for up to a year
  • risk factors
    • exposure to cats
• Presentation
  • immunocompetent patients
    • mononucleosis-like syndrome
  • immunosuppressed patients
    • brain abscesses
    • focal neurologic deficits including aphasia, hemiparesis, and seizures
• Imaging and studies
  • serologic detection of immunoglobulins with enzyme linked immunosorbent assay (ELISA)
  • microscopy showing tachyzoites in blood or cerebral spinal fluid (CSF) 
  • brain MRI
    • multiple ring-enhancing lesions 
• Treatment
  • sulfadiazine and pyrimethamine
• immunosuppressed patients

Naegleria fowleri

• Introduction 
  • clinical syndrome
    • meningoencephalitis 
  • risk factors
    • swimming in warm freshwater
  • pathogenesis
    • protozoa enters the CNS via cribriform plate
  • prognosis
    • fatal in majority of cases within 1 week
• Presentation 
  • sudden headache
  • photophobia and stiff neck
  • altered sense of taste or smell
  • nose bleeds
  • altered mental status
• Imaging and studies
  • cerebral spinal fluid
    • presence of motile trophozoites  
    • elevated pressure
  • culture and direct fluorescence antibody stain 
  • brain CT
    • obliteration of cisternae and subarachnoid spaces
• Treatment
• amphotericin B

Trypanosoma brucei

• Introduction
  • clinical syndrome
    • African sleeping sickness or African trypanosomiasis
  • transmission via tsetse fly bite
  • demographics
    • endemic to sub-Saharan Africa
  • prognosis
    • good prognosis if treated appropriately
• Presentation
  • early stage
    • chancre at bite site
    • intermittent fevers, malaise, myalgia, and arthralgia
    • lymphadenopathy
    • facial edema
    • transient rash (urticarial or macular) 2 months after onset
  • late stage
    • persistent headaches
    • daytime somnolence and nighttime insomnia (African sleeping sickness)
    • weight loss
• Imaging and studies
  • peripheral blood smear with trypomastigotes 
  • card agglutination test for trypanosomiasis (CATT)
    • results available immediately
    • high sensitivity (96%)
  • lymph node biopsy
  • CSF studies
    • visualization of trypanosome
    • detection of immunoglobulins
• Treatment 
  • suramin
    • for early stage disease
  • melarsoprol
• for late stage disease or CNS involvement

Acanthamoeba

• Introduction
  • clinical syndrome
    • granulomatous amoebic encephalitis
  • risk factors
    • immunosuppression
  • transmission
    • via nasopharyngeal or breaks in skin
  • pathogenesis
    • cysts are dormant and resistant to treatment
    • trophozoites are infective and replicate via fission
  • prognosis
    • high rate of mortality
• Presentation
  • headache
  • photophobia and stiff neck
  • altered mental status
  • skin lesions
    • ulcers, nodules, or abscesses
• Imaging and studies
  • cerebral spinal fluid
    • presence of amoebas
    • elevated pressure
  • brain CT
    • nonspecific findings of single or multiple low-density masses with hydrocephalus
  • brain or skin biopsy 
    • granulomas, necrosis, amoebas, and inflammatory infiltrates
• Treatment
  • no first-line treatment is recommended
  • a combination of antibiotics and antifungals are usually used
• Complications
• residual vision or hearing impairment