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

Primary Category
Secondary Category


  • Parasitic infections present systemically, including in the central nervous system (CNS).
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.


  • 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.


  • Parasitic CNS infections are generally classified into two groups
    • Single-celled (protozoa)
    • Multicellular helminth (metazoa).
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
Mode of transmission
Geographic region
Taenia Solium
Fecal-oral; Eggs ingestion
Worldwide, mostly in Sub-Saharan Africa and Asia
Contaminated water/food, contact with infected animals
Middle East, Europe, Pacific, Latin America; Inuit populations in North America
Schistosoma species
Skin penetration
Tropical and sub-tropical regions; mostly in Africa, Asia, and Latin America.
Toxoplasma gondii
Oral-fecal: Oocytes/cysts ingestion from cat’s feces, undercooked meat Transplacentally
Worldwide, mostly in Sub-Saharan Africa and Asia
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
Chagas disease
Trypanosoma cruzi
Insect bite: triatomine bug
Latin America
Sleeping sickness
Trypanosoma brucei.
Insect bite: Tsetse fly
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.

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.


  • 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.


  • 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.


  • 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.


  • 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 - (n.d.). Retrieved February 9, 2022, from


  • JE;, P. (n.d.). Pathology of CNS parasitic infections. Handbook of clinical neurology. Retrieved February 9, 2022, from
  • Abdel Razek AA, Watcharakorn A, Castillo M. Parasitic diseases of the central nervous system. Neuroimaging Clin N Am. 2011 Nov;21(4):815-41, viii. doi: 10.1016/j.nic.2011.07.005. Epub 2011 Sep 3. PMID: 22032501.
  • Carpio, A., Romo, M. L., Parkhouse, R. M. E., Short, B., & Dua, T. (2016). Parasitic diseases of the central nervous system: Lessons for clinicians and policy makers. Expert review of neurotherapeutics. Retrieved February 9, 2022, from
  • Weiss, L. M., & Dubey, J. P. (2009, July 1). Toxoplasmosis: A history of clinical observations. International journal for parasitology. Retrieved February 9, 2022, from
  • Visser LG, Polderman AM, Stuiver PC. Outbreak of schistosomiasis among travelers returning from Mali, West Africa. Clin Infect Dis. 1995 Feb;20(2):280-5. doi: 10.1093/clinids/20.2.280. PMID: 7742430.
  • Ferrari TC. Spinal cord schistosomiasis. A report of 2 cases and review emphasizing clinical aspects. Medicine (Baltimore). 1999 May;78(3):176-90. doi: 10.1097/00005792-199905000-00004. PMID: 10352649.
  • Carod-Artal FJ. Neurological complications of Schistosoma infection. Trans R Soc Trop Med Hyg. 2008 Feb;102(2):107-16. doi: 10.1016/j.trstmh.2007.08.004. Epub 2007 Oct 1. PMID: 17905371.
  • Svenson JE, MacLean JD, Gyorkos TW, Keystone J. Imported malaria. Clinical presentation and examination of symptomatic travelers. Arch Intern Med. 1995 Apr 24;155(8):861-8. doi: 10.1001/archinte.155.8.861. PMID: 7717795.
  • White, A. C., Coyle, C. M., Rajshekhar, V., Singh, G., Hauser, W. A., Mohanty, A., Garcia, H. H., & Nash, T. E. (2018, April 3). Diagnosis and treatment of neurocysticercosis: 2017 clinical practice guidelines by the Infectious Diseases Society of America (IDSA) and the American Society of Tropical Medicine and Hygiene (ASTMH). UTMB Health Research Expert Profiles. Retrieved February 9, 2022, from
  • ; (n.d.). Prevention and control of schistosomiasis and soil-transmitted helminthiasis. World Health Organization technical report series. Retrieved February 9, 2022, from
  • Tsang VC, Wilkins PP. Immunodiagnosis of schistosomiasis. Screen with FAST-ELISA and confirm with immunoblot. Clin Lab Med. 1991 Dec;11(4):1029-39. PMID: 1802520.
  • Sulahian A, Garin YJ, Izri A, Verret C, Delaunay P, van Gool T, Derouin F. Development and evaluation of a Western blot kit for diagnosis of schistosomiasis. Clin Diagn Lab Immunol. 2005 Apr;12(4):548-51. doi: 10.1128/CDLI.12.4.548-551.2005. PMID: 15817765; PMCID: PMC1074383.
  • Ferrari TC. A laboratory test for the diagnosis of neuroschistosomiasis. Neurol Res. 2010 Apr;32(3):252-62. doi: 10.1179/016164110X12644252260718. PMID: 20406603.
  • Abanyie FA, Arguin PM, Gutman J. State of malaria diagnostic testing at clinical laboratories in the United States, 2010: a nationwide survey. Malar J. 2011 Nov 10;10:340. doi: 10.1186/1475-2875-10-340. PMID: 22074250; PMCID: PMC3225402.
  • White NJ. The treatment of malaria. N Engl J Med. 1996 Sep 12;335(11):800-6. doi: 10.1056/NEJM199609123351107. PMID: 8703186.
  • Walker, M. D., & Zunt, J. R. (2005). Neuroparasitic infections: cestodes, trematodes, and protozoans. Seminars in neurology25 (3), 262–277.
  • Ma P, Visvesvara GS, Martinez AJ, Theodore FH, Daggett PM, Sawyer TK. Naegleria and Acanthamoeba infections: review. Rev Infect Dis. 1990 May-Jun;12(3):490-513. doi: 10.1093/clinids/12.3.490. PMID: 2193354.
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