Parasitic CNS Infections

Primary Category

Neuroinfectious

P-Category

Secondary Category

S-Category

Authors

Ha Phan Thann Le MD
Junaid Kalia MD

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	ㅤ	ㅤ	ㅤ
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	ㅤ	ㅤ	ㅤ
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.

Bibliography

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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 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4926779/

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