Parasitic diseases of the central nervous system: lessons for clinicians and policy makers

Figures & data

Table 1. Classification of parasitic infections of the central nervous system.

Protozoa	Metazoa
Malaria	Flatworms	Trematoda	Schistosomiasis
American trypanosomiasis			Paragonimiasis
African trypanosomiasis		Cestoda	Cysticercosis
Toxoplasmosis			Coenurosis
Amebiasis			Hydatidosis
Microsporidiasis			Sparganosis
Leishmaniasis	Roundworms or Nematoda	Gnathostomisasis
		Angiostrongyliasis
		Toxocariasis
		Strongyloidiasis
		Filariasis
		Baylisascariasis
		Dracunculiasis
		Dicronemiasis
		Lagochilascariasis

Table 2. Characteristics of main parasitic infections of the central nervous system.

Parasite disease	Causative organism	Vector/intermediate host	Mode of transmission	Endemic regions
Taeniasis/Cysticercosis	Taenia solium	Pigs, humans	Fecal–oral, ingestion of eggs from human feces (ingestion of larval cyst from pig muscle leads to taeniasis)	Widespread throughout rural areas, with poor sanitation, where humans and pigs cohabitate: Latin America, Africa, Asia
Toxoplasmosis	Toxoplasma gondii	Cats, intermediate hosts in nature (including birds and rodents)	Ingestion of oocysts (cat feces) or tissue cysts (undercooked meats), blood transfusion, transplacentally from mother to fetus	Worldwide, greatest burden in Sub-Saharan Africa and Asia
Echinococcosis (Hydatidosis)	Echinococcus granulosus, Echinococcus multilocularis	EG: Sheep, goats, cattle, pigs, yaks or other farm animals EM: Small mammals (rodents and lagomorphs)	Ingestion of contaminated soil, water or food, contact with infected animals	Middle East, Europe, Pacific, Latin America; Inuit populations in North America
Schistosomiasis	Schistosoma japonicum, mansoni, and haematobium	Fresh water snail	Penetration of skin by cercariae in freshwater	Tropical and subtropical areas of Sub-Saharan Africa, Latin America and Asia
Paragonimiasis	Paragonimus westermani	Freshwater snails, crustacean-eating mammals	Fecal–oral, raw, undercooked freshwater crustaceans	East and Southeast Asia, West and Central Africa, Central and South America
Malaria	Plasmodium falciparum	Vector borne, Anopheles mosquito	Insect bite	Tropics from Sub-Saharan Africa, Latin America, Asia and Oceania
Toxocariasis	Toxocara canis, Toxocara cati	Cats, humans	Fecal–oral, contaminated soil	Worldwide
Onchocerciasis	Onchocerca volvulus	Blackfly (Similium)	Insect bite	West and Central Africa, as well as parts of Central and South America
Chagas disease	Trypanosoma cruzi	Triatomine bug	Insect bite	Latin America
African trypanosomiasis	Trypanosoma brucei gambiense, Trypanosoma brucei rhodesiense	Tsetse fly	Insect bite	Africa

Figure 1. Parasitic diseases of central nervous system according to presentation.

Figure 2. Imaging findings in patients with neurocysticercosis. A) MRI of parenchymal vesicular cyst with scolex. B) MRI of colloidal cysticerci with perilesional edema. C) CT scan of many calcified parasites. D) MRI of intraventricular cysts.

Table 3. Currently available antiparasitic drug regimens for parasitic infections of the CNS.

Neurocysticercosis	Albendazole with corticosteroids Praziquantel (alternative to albendazole) with corticosteroids Combined albendazole/praziquantel with corticosteroids if >2 active parenchymal cysts
Toxoplasmosis	Sulfadiazine + pyrimethamine with leucovorin Clindamycin (or atovaquone) + pyrimethamine with leucovorin (alternative) Trimethoprim-sulfamethoxazole (alternative)
Echinococcosis	Albendazole or mebendazole (alone or with surgery)
Schistosomiasis	Praziquantel (after starting corticosteroid treatment)
Paragonimiasis	Praziquantel Triclabendazole
Cerebral malaria	Severe falciparum malaria IV artesunate IV quinine dihydrochloride or quinidine gluconate ∘ + doxycycline, tetracycline, or clindamycin
Toxocariasis	Albendazole with corticosteroids Mebendazole (alternative to albendazole) with corticosteroids
Onchocerciasis	Ivermectin Doxycycline
American trypanosomiasis	Acute or chronic infection Benznidazole Nifurtimox
African trypanosomiasis	Early infection Trypanosoma brucei gambiense ∘ Pentamidine ∘ Suramin (alternative) Trypanosoma brucei rhodesiense ∘ SuraminLate infection Trypanosoma brucei gambiense ∘ Eflornithine + nifurtimox ∘ Eflornithine monotherapy ∘ Melarsoprol (alternative) with corticosteroids Trypanosoma brucei rhodesiense Melarsoprol
Angiostrongyliasis	None (corticosteroids and symptomatic treatment only)

Table 4. Approximate prevalence and disability-adjusted life years (DALYs) of common parasitic infections.

Parasitic disease	Approximate worldwide prevalence	Estimated DALYs (in millions) – From Global Burden of Disease (GBD) 2010 (95% CI)
Cysticercosis	50 million	0.50 (0.38–0.66)
Echinococcosis (Hydatidosis)	1 million	0.14 (0.07–0.29)
Schistosomiasis	207 million	3.31 (1.70–6.26)
Malaria	214 million	82.7 (63.4–109.8)
Onchocerciasis	42 million	0.49 (0.36–0.66)
American trypanosomiasis	10 million	0.55 (0.27–1.05)
African trypanosomiasis	50,000 to 70,000	0.56 (0.08–1.77)

Figure 3. Countries and areas at risk for cysticercosis.

Reprinted from: World Health Organization. Assembling a Framework for Intensified Control of Taeniasis and Neurocysicercosis caused by Taenia solium, 2013. Available at: http://apps.who.int/iris/bitstream/10665/153237/1/9789241508452_eng.pdf?ua=1 [Last accessed 29 December 2015].