Parasitic Meningitis Causes And Symptoms

Overview

Parasitic meningitis is a form of meningitis that infects the brain. Meningitis is an infection of the meninges (membranes around the spinal cord and brain), and there are different forms including viral, bacterial, and parasitic.¹ Parasitic meningitis is a rare but formidable disease which largely affects animals but can occur in people through contaminated water or infected foods/animals.² The most common symptoms that present first are: an intense sudden onset headache, stiff neck and nausea.³ In the UK alone, a charity called Meningitis Now estimates that there are up to 8,000 cases of the disease in the UK every year.⁴ There are 2 types of parasitic meningitis: Primary Amebic Meningoencephalitis (PAM) and Eosinophilic Meningitis (EM). PAM is an extremely rare infection in humans, however is rapidly fatal. EM is more common but is associated with less severe symptoms with a mortality rate of around 1%.⁵ In this article, we’re on a mission to shed light on the different types of parasitic meningitis, discover their symptoms and causes, and guide you through the clinical journey of the disease. 

Causes of Parasitic Meningitis

Primary Amebic Meningoencephalitis (PAM)

PAM is caused by the amoeba Naegleria fowleri and is typically fatal, however, it is very rare and has an average prevalence of 2-3 cases a year in the US.⁶ The amoeba is typically found in bodies of water such as freshwater lakes, poorly chlorinated pools, polluted water, and hot springs.⁷ It is transmitted up the nose as people usually pick it up when swimming in the infected waters. After entering through the nose it then moves into the respiratory system where it passes through a special bone at the base of the skull called the cribriform plate into the Central Nervous System (CNS).⁸ The infection is highly fatal due to the severity of the immune response from the body that the amoeba elicits, resulting in the destruction of functional brain tissue, swelling and haemorrhaging.⁹  

Eosinophilic Meningitis (EM)

EM is the more common form of parasitic meningitis and is most commonly picked up by eating poorly cooked/raw fish, snails, slugs and contaminated vegetables.¹⁰ There are 3 main parasites that can cause EM:¹ 

Angiostrongylus cantonensis - neurologic angiostrongyliasis 

A.cantonesis is the most common cause of EM and is not typically found in western countries but more localised to SouthEast Asia.¹¹ The organism can infect people through ingestion, it then migrates to the brain where tissue becomes damaged due to the movements of the worms.¹²

Baylisascaris procyonis - neural larva migrans 

This organism is a roundworm which typically infects racoons but there have been 20 recognised human instances in children under the age of 2.¹³ Infection can occur when the children ingest materials that are contaminated with the Baylisascaris eggs.¹⁴

Gnathostoma spinigerum - neurognathostomiasis 

Once in the body, gnathostoma larvae first migrate to the gastrointestinal system, and can spread to the skin, auditory systems, CNS and the eyes.¹⁵ The larvae can get into the CNS through the opening of the skull or openings in the spine both near cranial/spinal nerves and blood vessels.¹⁶ The spread of this organism throughout the body can take as long as several years.¹⁷

Common symptoms and treatment of parasitic meningitis

Primary Amebic Meningoencephalitis (PAM)

The early symptoms present as:¹⁸

• Fever
• Headaches
• Nausea and vomiting
• Fatigue
• Sore throat

Later progression involves:

• Stiff neck
• Sensitivity to light 
• Hallucinations
• Seizures  

The first line of treatment recommended by the CDC is Amphotericin B (AMB) which is the most widely used.¹⁹ As previously mentioned, although the mortality rate of this type of infection is extremely high, the incidence is very low. 2 of the 3 reported survivors underwent controlled hypothermia and showed full neurological recovery.^20,21 This is a technique that involves cooling body temperature and is normally used to improve neurological recovery for people who have had a heart attack.²²

Eosinophilic Meningitis

Symptoms of EM and percentage experienced by case studies:²³

• Headache, 100%
• Light sensitivity and visual disturbance, 92%
• Stiff neck, 83%
• Fatigue, 83%
• Hyperesthesia (extreme sensitivity to touch, pain, and pressure), 75%
• Vomiting, 67% 
• Paresthesias (burning/prickling sensation in hands, arms, legs, feet, 50%

Treating EM primarily focuses on alleviating the symptoms with medicine such as corticosteroids that can reduce the length of a headache.²⁴ The outlook for most patients is generally very positive as the symptoms improve within a few weeks and long-term problems are rare. When the parasite reaches the stomach, severe stomach pain, nausea and vomiting begin and lasts for up to 2-3 weeks before resolving completely.²⁵

Diagnosis

The diagnosis of parasitic meningitis proves to be difficult as it is often hard to locate the parasites in the body. 

Laboratory tools and testing

Diagnosing EM mainly relies on laboratory testing at blood samples and most commonly Cerebrospinal Fluid (CSF). It is characterised by having 10 or more eosinophils (white blood cells indicative of an infection in the body) per litre of CSF, although this isn't necessarily definitive of parasitic meningitis.²⁶ The gold standard for diagnosing the infection looks to find juvenile forms of the parasite within the CSF. Due to the limited volume obtained for testing, this is not viable in many cases. If EM is suspected, a technique called Western blot analysis is used to look for antibodies against the parasites that can cause EM.^27,28 A dot-blot ELISA is a test used to detect the body's antibodies or antigens against the parasite and is thought to have 100% accuracy.²⁹

Other Techniques

While brain scans like a Computed Tomography (CT) won’t show many abnormalities, Magnetic Resonance Imaging (MRIs) can reveal certain changes such as an enlarged Virchow-Robin space (spaces that surround blood vessels) and bright spots around the centre of the brain. As well as these tools, doctors will look at your travel history to help determine the diagnosis. The parasites that cause EM in particular are mainly found in Southeast Asia, the Pacific Islands and various parts of the US.¹ 

Diagnosis of primary Ameba Meningitis 

PAM is clinically indistinguishable from bacterial meningitis. Moreover, most people typically die between 5-10 days of onset due to the severity of the disease.³⁰ The diagnosis for PAM usually starts by looking at the history of swimming in fresh water. Typical CT and CSF tests aren’t sufficient for a full diagnosis so a special technique called Giemsa staining can identify the presence of the Naegleria fowleri.³¹

Difficulty of diagnosis

It can be challenging to distinguish parasitic meningitis from other forms of meningitis such as bacterial, particularly in sub-Saharan African countries where it is the most prevalent.³² In developing countries, the resources needed to diagnose these different types of meningitis are largely not accessible.

Prevention

PAM prevention

The parasites that cause the fatal PAM cannot survive in water that is cool, clean and treated with chlorine. Here are some precautions that you can follow to lower your risk of infection:³³

• Avoid swimming in warm fresh water bodies or pools
• Keep your head above the water's surface when in these bodies of water 
• Ensure that the bodies of water are properly chlorinated and maintained 
• In untreated water, be careful that water doesn’t get up your nose
• Always supervise children playing in bodies of water, as this infection is commonly seen in younger generations
• The CDC recommends to seek medical attention should you develop fever, headache or vomiting after swimming in fresh water with the initial symptoms typically showing at 5 days after infection⁷

EM prevention

For EM, there is currently no approved vaccines for the prevention of this disease however there are a few precautions that can be taken:³⁴

• Ensuring that snails, slugs, freshwater fish, shrimp, frogs and crabs are cooked thoroughly
  • Avoid eating any of the above when they have been marinaded or refrigerated only 
• Wash all vegetables before consuming them raw 
• Washing hands should you ever handle pet African snails or clean their enclosures 
• Reduce and manage populations of primary hosts of the infection such as rodents
  • Avoid populations/use rodenticides 
• Reduce and manage population of intermediate hosts such as snails and slugs
  • Avoid populations/use molluscicides

Summary

This article has delved into the world of parasitic meningitis, specifically, Primary Amebic Meningitis (PAM) and Eosinophilic Meningitis (EM). PAM is a very serious and fatal infection of the brain however it is extremely rare in humans. Although EM is more common, the symptoms resolve themselves and it is often mistaken for food poisoning! Distinguishing parasitic meningitis from other types of meningitis and various other diseases can be complex, particularly in regions with a shortage of healthcare resources. While there are limited cures for these types of meningitis, prevention strategies play a crucial role in reducing the risk of infection.