Parasitic CNS Infections

CNS parasitic involvement is associated with high morbidity and mortality. • Depending on the infection stage, location, and host immunization, CNS parasitic infections can cause local or widespread damage

Introduction

  • Parasitic infections present systemically, including in the central nervous system (CNS).
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CNS parasitic involvement is associated with high morbidity and mortality.
  • Depending on the infection stage, location, and host immunization, CNS parasitic infections can cause local or widespread damage.
  • Clinical CNS associations are encephalitis, meningitis, myelitis, cerebral cysts, and cerebral calcification.

Pathophysiology

  • Parasites enter the body directly through the 2 most common pathways:
    • Skin
    • Gastrointestinal tract
    • Other parasites can enter through insect bites.
  • Parasites invade CNS mostly through the blood
    • After entering the body → circular blood → blood-brain barrier → brain.
    • In some cases, the parasite invades the olfactory neuroepithelium → subarachnoid space/neural skulls foramina → the brain.

Etiology

  • Parasitic CNS infections are generally classified into two groups
    • Single-celled (protozoa)
    • Multicellular helminth (metazoa).
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The most common CNS infection is cysticercosis.
  • Less frequent infections are toxoplasmosis, echinococcosis, schistosomiasis, paragonimiasis, malaria, toxocariasis, onchocerciasis, and Chagas disease (American trypanosomiasis), sleeping sickness (African trypanosomiasis), and angiostrongyliasis.

Table 1: Characteristics of Parasitic CNS Infections

Parasitic disease
Pathogen
Mode of transmission
Geographic region
Metazoa
Cysticercosis
Taenia Solium
Fecal-oral; Eggs ingestion
Worldwide, mostly in Sub-Saharan Africa and Asia
Echinococcosis
Echinococcus
Contaminated water/food, contact with infected animals
Middle East, Europe, Pacific, Latin America; Inuit populations in North America
Schistosomiasis
Schistosoma species
Skin penetration
Tropical and sub-tropical regions; mostly in Africa, Asia, and Latin America.
Protozoa
Toxoplasmosis
Toxoplasma gondii
Oral-fecal: Oocytes/cysts ingestion from cat’s feces, undercooked meat Transplacentally
Worldwide, mostly in Sub-Saharan Africa and Asia
Malaria
Plasmodium falciparum
Insect bite
Tropics from Sub-Saharan Africa, Latin America, Asia, and Oceania
Primary amoebic meningoencephalitis
Naegleria fowleri
Olfactory penetration through swimming, bathing, diving
Worldwide.
Chagas disease
Trypanosoma cruzi
Insect bite: triatomine bug
Latin America
Sleeping sickness
Trypanosoma brucei.
Insect bite: Tsetse fly
Africa
Derived from Carpio, A., Romo, M. L., Parkhouse, R. M., Short, B., & Dua, T. (2016). Parasitic diseases of the central nervous system: lessons for clinicians and policymakers. Expert review of neurotherapeutics, 16 (4), 401–414. https://doi.org/10.1586/14737175.2016.1155454

Clinical manifestations

Neurocysticercosis (NCC)

  • Intraparenchymal NCC
    • Common: seizure, headache
    • Less common: altered vision, focal neurologic signs, and meningitis.
  • Extraparenchymal NCC
    • Appears in ventricles, subarachnoid space, spine, and/or the eye
    • Elevated intracranial pressure: headache, nausea, and vomiting.
    • Accompanied by altered mental status.
  • Extraparenchymal NCC occurs in >60% of cases while intraparenchymal NCC carries higher complications than extraparenchymal NCC.
  • Extraneural cysticercosis: Asymptomatic nodule 0.5-2cm in diameter, calcified cysts in muscular and subcutaneous tissues.

Toxoplasmosis

  • Cerebral toxoplasmosis subtype
    • Immunocompetent: Asymptomatic
    • Immunocompromised: Altered mental status, seizure, weakness, cranial nerves deficits, sensory abnormalities.
  • Congenital infection
    • Microcephaly
    • Hydrocephaly
    • Chorioretinitis
    • Hepatosplenomegaly, jaundice
    • Rash, petechia
    • Developmental delay
    • Anemia.

Echinococcosis

  • Ruptured or super-infected cysts can cause severe infection.
  • Associated with the space-occupying lesion, increase intracranial pressure: headache, nausea, vomiting, and seizures.
  • Some Echinococcus can secondarily infect the CNS from either the liver or lungs.

Schistosomiasis

  • Swimmer itch
    • Localized dermatitis: pruritic papular or urticarial rash at the larva’s entry site after swimming in freshwater
  • Acute Schistosomiasis syndrome (Katayama syndrome)
    • Appears 3-10 weeks after infection, associated with swimming, bathing, diving, skiing in freshwater.
    • Sudden onset of fever, urticaria, angioedema, chills, myalgias, arthralgias, dry cough, diarrhea, abdominal pain, and headache.
    • Severe infection can cause acute myelopathy, encephalitis
  • Chronic infection
    • Symptoms depend on the infected organs: intestinal, liver, lung, urinary tract, and CNS.
  • Neuroschistosomiasis
    • Spinal cord involvement
      • Lower limb pain, lower motor dysfunction
      • Bladder paralysis
      • Bowel dysfunction.
    • Brain involvement
      • Delirium, loss of consciousness
      • Seizures
      • Dysphasia, visual field impairment
      • Focal motor deficits
      • Ataxia.

Malaria

  • Uncomplicated malaria
    • Mild symptoms of malaria and absence of severe malaria
    • Symptoms of mild malaria
      • Headache
      • Tachycardia, tachypnea
      • Chills, malaise, fatigue, diaphoresis
      • Anorexia, nausea, vomiting, abdominal pain, diarrhea
      • Arthralgias, myalgias
      • Anemia, and palpable spleen.
  • Complicated malaria
    • Altered consciousness
    • Respiratory distress, circulatory collapse
    • Metabolic acidosis, hypoglycemia
    • Renal failure, hemoglobinuria
    • Hepatic failure
    • Coagulopathy, severe anemia, or massive intravascular hemolysis.
  • Cerebral malaria
    • Onset: gradual or sudden following a convulsion
    • Symptoms: impaired consciousness, delirium, and/or generalized seizures; focal neurologic signs are unusual

Primary amoebic meningoencephalitis

  • Acute hemorrhagic meningoencephalitis
  • Symptoms
    • High fever
    • Severe headache, photophobia, nausea, vomiting, meningeal signs
    • Behavioral abnormalities, smell and taste abnormalities
    • Cranial nerve palsy
    • Altered mental status, seizures
  • Rapid progression and high mortality rate: rapid, profound alter mental status, severe cranial hypertension → herniation, and death in a few days.

Chagas disease (American Trypanosomiasis)

  • Acute phase
    • Fever
    • Generalized lymphadenopathy
    • Hepatosplenomegaly
    • Swelling at the bite site
    • Unilateral painless edema of eyelids and periocular tissue.
  • Chronic phase: mainly involved in cardiomyopathy, gastrointestinal tract.
  • CNS involvement in a small percentage of patients in the acute phase. In the chronic phase, CNS involvement mainly presents as meningoencephalitis.

Sleeping sickness (African Trypanosomiasis)

  • Hemolymphatic phase
    • Intermittent fever
    • Painless cervical lymphadenopathy in the posterior triangle of the neck (Winterbottom’s sign)
    • Hepatosplenomegaly
    • Cutaneous symptoms: erythematous, targetoid, nodular, ulcer
    • Anemia, facial edema.
  • Neurologic phase
    • Headache
    • Behavioral changes: apathy, psychosis, confusion
    • Daytime somnolence, nighttime insomnia
    • Ataxia, rigidity
    • Hypothermia/hyperthermia
    • Coma.

Further Reading

  • Breakdown of parasitic CNS infections - web.stanford.edu. (n.d.). Retrieved February 9, 2022, from https://web.stanford.edu/group/parasites/ParaSites2010/Adnan_and_Rehan_Syed/Parasites%20and%20Pestilence%20Paper_ParaSites%20Submission%20for%20Carlos%20Seligo_Rehan%20Syed%20and%20Adnan%20Syed.doc

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