Neurological infections

The 8 most parasitic infestations of the nervous system

They will use any natural orifice to gain access to our bodies, or they will create their own. They will burrow and nibble their way to the most accommodating organ they can find, and then latch on with hookstentacles, or just sheer determination. They will permanently ingratiate themselves to their unwary and unwelcoming hosts. They will use every trick and guile to perpetuate their species. We call them parasites, but they see themselves as survivors.

By Magdalena ZZOwn work, CC BY-SA 3.0, Link

Parasites set out on a mission to cause just enough damage to incapacitate their benefactors, but falling just short of totally annihilating them. These creatures are too wise to pursue a course of mutually assured destruction; they have not survived the centuries by killing the goose that lays the golden eggs.

By Rjgalindo, CC BY-SA 3.0, Link

The global destruction inflicted by parasites far outstrips the combined harm of many popular neurological diseases, not that one could tell by reading the key journals. Parasites have learned to avoid the limelight by thriving on the weak and deprived, the dregs of the earth who live in the backwaters of the world. In this way they avoid the curiosity of the headline writers, and evade the attention of health policy makers.

By GanímedesOwn work, CC BY-SA 4.0, Link

Parasites have had the upper hand over humanity for eons even though they are not faceless aliens or strange extraterrestrials. On the contrary, we have mastered their complex biology, and we know their intricate life cycles like the backs of our hands. We have charted their natural habitats, defined their intermediate hosts, and know their strengths and weaknesses. But, somehow, these cestodes and nematodes, these protozoa and trematodes, continue to evade our traps, perhaps even sniggering at our futile efforts to eradicate them.

By Alan R WalkerOwn work, CC BY-SA 3.0, Link

The brain is a favoured organ for many parasites. They recognise that the highly nutritious habitat of the nervous system provides succour for the teeming generations they lets loose on their hosts daily. By disabling the brain, they limit the host’s capacity for strategic planning to mount a counterattack. By hiding behind the blood-brain barrier, they tactically evade the body’s immune defences. Who are these most tenacious of ingenious invaders? In no specific order of virulence, (pardon the pun), here is our shortlist of the eight most parasitic infestations of the nervous system.



By image by Ute Frevert;false color by Margaret Shear –, CC BY 2.5, Link

This infestation is caused by Plasmodium falciparum, a parasite which primarily infects red blood cells. Using a membrane protein called PfEMP1, it adheres to the walls of blood vessels thereby clogging the brain’s blood supply. It causes further damage by breaking down red cells, haemolysis, and by disrupting the blood-brain barrier. Check out more on cerebral malaria in the neurochecklists:



Toxoplasmosis. Pseudocyts containing bradyzoites. Yale Rosen on Flickr.

The harbinger of neurotoxoplasmosis is Toxoplasma gondii. Humans acquire this by ingesting raw meat or drinking water contaminated by cat faeces. It may also be transmitted congenitally from mother to child. The parasite goes through different developmental phases which the biologists have labelled sporozoites, bradyzoites, and tachyzoites! See more in the neurochecklists:



By USCDC –, Public Domain,

Naegleria fowleri, the causative parasite of PAM, is a thermophylic free-living amoeboflagellate. It accesses the nervous system through the nose, casually destroying the olfactory bulbs and orbitofrontal cortex in the process. The typical victim of N. Fowleri is someone who swims in freshwater or geothermal springs, or who ritually rinses the nose with neti pots. Read all about PAM in the neurochecklist:



Tsetse fly. Oregon State University on Flickr.

The twin agents of sleeping sickness are Trypanosoma brucei gambiense and rhodesiense. The are transmitted by the dreaded tsetse fly, and they cause two forms of the disease: the early hemolymphatic stage in blood and lymph nodes, and the later meningoencephalitic stage in the central nervous system. They leave a trail of destruction in their path, from a skin trypanosomal chancre, to the classical Winterbottom sign: rubbery lymph nodes in the neck. Much more on these two parasites, and their equally nefarious cousin Trypanosoma cruzi, in the neurochecklists:



By علاءOwn work, CC BY-SA 4.0, Link

There are three major species of schistosoma that bedevil humans, all with fancy names: mansoni, haematobium, and japonicum. Their intermediate hosts are snails which inhabit fresh water and where they lay their eggs. These ova reach the nervous system either through arteries or via the Batson vertebral epidural venous plexus. More on these creatures in the neurochecklists:



By IndmanuabaOwn work, CC BY-SA 3.0, Link

The pig is the natural ally of Taenia solium, the pork tapeworm that causes the much feared neurocysticercosis. The disease is classified into parenchymal and extra-parenchymal forms, and these classically present with epilepsy and hydrocephalus respectively. The parasite has a striking appearance on brain imaging, multiple cysts containing a scolex visible to the trained eye. There is more to neurocysticercosis in the neurochecklists:



By United States Department of Agriculture – From [1], Public Domain, Link

The parasite Onchocerca volvulus is a filaria worm which is transmitted by the black fly species, Simulium. It is a burrowing worm which is found just under the skin, from where it releases loads of baby microfilaria daily. It is of interest to neurologists because it causes two forms of seizure disorder: onchocerciasis associated epilepsy (OAE) and nodding syndrome. It also causes Nakalanga syndrome which is associated with mental retardation. For more details, check out the following neurochecklists:



By GanímedesOwn work, CC BY-SA 4.0, Link

Last, but by no means the least, comes Echinococcus granulosus, the agent of cerebral echinococcosis or hydatid disease. Echinococcus eggs are transmitted through the faeces of canines such as dogs and wolves. The full blown disorder, hydatid disease, is a scourge of the nervous system, manifesting as seizures, focal deficits, raised intracranial pressure, and cranial nerve palsies. Radiologists recognise hydatid disease by its tell-tale water lily sign on CT scans. Check out more in the neurochecklists:



And this is just the tip of an infernal iceberg of parasitic infestations. Check out the full list of parasites in the neurochecklist:

Parasitic infections of the nervous system: classification

Red blood cells infected with malaria. NIH Image gallery on Flickr.
Neurological infections

The 7 most devastating viral neurological infections

One may be forgiven for thinking that neurology is all about neuroinflammatory and neurodegenerative diseases. This is because these disorders seem to get a lot of attention. But nothing could be further from the truth-globally, infections impose a heavier burden on neurological practice than say Multiple Sclerosis (MS) or Parkinson’s disease (PD). And medical advances have done very little to deter all sorts of creatures from invading the nervous system.

Bacteria. Cesar Herada on Flikr.

The major types of organisms that infect the nervous system are viruses and bacteria, but fungi and parasites also take their toll. In this blog we will focus on the 7 most devastating viral neurological infections.

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1.  Viral encephalitis

Encephalitis is infection of the brain substance, as opposed to meningitis which is infection of the covering of the brain. Viral encephalitis, for some reason, tends to favour the temporal lobes of the brain causing seizures and memory problems, amongst other symptoms. The main villain responsible for viral encephalitis is herpes simplex type 1 (HSV1), but almost every other virus can carry out the job with deadly precision. The list is long and includes geographically specific viruses as West Nile and Japanese B. Check out the full list of causes of viral encephalitis and its management.

Herpes Simplex Virus Type 1: Procapsid and Mature Capsid. NIH Image gallery on Flikr.

2. HIV associated neurological infections

No part of the nervous system is immune to the ravages of the dreaded HIV. The list includes HIV  associated neurocognitive disorders (HAND)myelopathiesneuropathies, drug-induced syndromes, and tumours. The worst aspect of HIV, of course, is that it opens the flood gates for opportunistic infections to invade the nervous system.

By BruceBlausOwn work, CC BY-SA 4.0, Link

3. Hepatitis E virus (HEV)

Hepatitis E virus is just emerging as a scourge of neurology. It is particularly villainous because of its protean manifestations, from Guillain Barre syndrome (GBS) to neuralgic amyotrophy (brachial neuritis), from transverse myelitis to idiopathic intracranial hypertension (IIH). Check out the full neurological manifestations of HEV.

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4. Influenza H1N1

Influenza is bad, and H1N1 is a particularly nasty variant. This subtype of Influenza A is epidemic in pigs and birds, and unleashes havoc when it crosses over to humans. Its nervous system manifestations include encephalopathyGuillain Barre syndrome (GBS), acute demyelinating encephalomyelopathy (ADEM), and stroke. Not one to be treated lightly at all. Check out everything about Influenza H1N1 and the different ways influenza affects the nervous system.

H1N1 influenza viral particles. NIAID on Flikr.

5. Zika virus infection (ZIKV)

This new kid on the infection block is fast establishing itself as a menace. Apart from causing myelitis, meningoencephalitis, encephalitis, encephalomyelitis, Guillain-Barre syndrome (GBS), and myasthenia gravis (MG), it is responsible for a variety of congenital defects, particularly microcephaly. Zika virus pathology and management are extensively covered in neurochecklists. Or check out 20 things we now know for certain about the Zika virus on our sister blog, The Neurology Lounge.

By Manuel Almagro RivasOwn work, CC BY-SA 4.0, Link

6. Ebola virus disease (EVD)

This ancient virus gained recent notoriety when it ravaged a large section of West Africa, sending chilling waves across the world. It is an RNA filovirus whose main reservoir is bats. It causes, among other things, an encephalitis and meningoencephalitis. It appears to be on vacation in the meantme, but it will surely rear its ugly head sometime soon. Check out the comprehensive clinical features and management of Ebola virus disease on neurochecklists.

By Scientific Animations –, CC BY-SA 4.0, Link

7. Varicella zoster virus (VZV)

The varicella virus must take the prize for the most diverse ways a virus affects the nervous system. Neurochecklists has listed >20 neurological manifestations of VZV, ranging from herpes zoster to post herpetic neuralgia (PHN), from meningitis to encephalitis. VZV also causes all forms of cranial and peripheral neropathy, and may result in stroke, aneurysms, and giant cell arteritis (GCA). Not to mention the curiously named progressive outer retinal necrosis (just don’t mention its acronym!). Check out the full VZV on neurochecklists.


Check out the other deadly viral neurological infections on neurochecklists:

Dengue virus infection (DENV)

West Nile virus (WNV) infection

Japanese encephalitis virus (JEV)

Rabies encephalitis