Parasitic Meningitis In Adults

Overview 

Parasitic meningitis is a rare form of meningitis disease, which causes inflammation of the protective membranes called meninges, around the brain and spinal cord. Bacterial and viral disease-causing meningitis are well known but parasitic meningitis is less frequent and a serious threat with high morbidity and mortality rates. Parasites are extremely small, and they can grow into long worms by feeding off their host and multiplying. The parasite is not a disease but can spread diseases. 

This type of meningitis can manifest in various clinical forms, ranging from acute to chronic, depending on the specific parasite involved, its life cycle, and the host's immune response. The geographic distribution of these parasites is influenced by environmental factors, with higher incidence in tropical and subtropical regions, though cases have been reported worldwide due to global travel and changing ecological patterns. This introduction aims to provide a comprehensive overview of parasitic meningitis in adults, setting the stage for a detailed exploration of its causes, clinical features, diagnostic approaches, treatment strategies, and preventive measures.

Common parasites causing meningitis 

Parasitic meningitis in adults is an uncommon but severe condition caused by a variety of parasites that infect the central nervous system (CNS), leading to inflammation of the meninges. There are three different types of parasites that can affect humans, which are protozoa, helminths and ectoparasites. 

The most common cause of parasitic meningitis is Naegleria fowleri called brain-eating amoeba. This is an organism that can cause Primary Amoebic Meningoencephalitis (PAM) which can be fatal in nearly all cases and granulomatous amebic encephalitis (GAE).¹ It can be found in contaminated lakes, ponds, rivers, and poorly maintained pools.² The next common type is eosinophilic meningitis, Angiostrongylus cantonensis³ commonly referred to as rat lungworm, is a leading cause of eosinophilic meningitis. The parasite's definitive hosts are rats, while intermediate hosts include snails and slugs. Baylisascaris procyonis⁴ an eosinophilic meningitis commonly called the raccoon roundworm, is a nematode with raccoons as its primary host. 

Several other parasites can cause meningitis in adults, though less commonly. These include Schistosoma spp., which can cause schistosomiasis,⁵ which can lead to neurological complications, including meningitis. Toxoplasma gondii, this protozoan is often associated with exposure to cats or undercooked meat. In immunocompromised individuals, it can lead to CNS infections, including meningitis. Trypanosoma spp., known for causing African sleeping sickness⁶ and Chagas disease (Trypanosoma cruzi), these parasites can affect the CNS and result in meningoencephalitis.

Clinical presentation and symptoms

The clinical presentation and symptoms of parasitic meningitis in adults can vary widely, depending on the parasite involved, the severity of the infection, and the host's immune response. While some cases may present typical signs of meningitis, others can manifest with unique or atypical symptoms includes, 

• A sudden intense headache
• Stiff neck or inability to move your neck forwards
• Nausea
• Vomiting
• Light sensitivity
• Confusion
• Painful sensation to touch on the skin
• Weak muscles
• Fever
• Permanent disability
• Coma
• Itchy rash
• A pins and needles sensation.

As parasitic meningitis progresses, the condition can lead to more severe symptoms and complications. Confusion, disorientation, and altered consciousness can occur as the infection impacts brain function. Seizures may develop due to increased intracranial pressure or direct damage to brain tissue. Neurological deficits include muscle weakness, sensory loss, cranial nerve abnormalities, or paralysis, depending on the affected areas of the brain and spinal cord. In severe cases, the infection can lead to coma and, if untreated, death.

 Certain parasites are associated with specific clinical presentations, which can help guide diagnosis and treatment.  Angiostrongylus cantonensis parasite is known to cause eosinophilic meningitis, it can also lead to peripheral nerve damage and hyperesthesia (increased sensitivity to touch). Baylisascaris procyonis parasite can lead to significant neurological damage due to larval migration in the CNS.¹¹

Transmission and risk factors

Parasitic meningitis in adults can be transmitted through various routes, depending on the specific parasite involved, from a range of environmental, behavioural, and demographic elements that contribute to an individual's likelihood of acquiring an infection. In most of the cases, humans are not the natural hosts but can acquire through various modes. 

• Consumption of contaminated food or water is a common transmission pathway. This includes eating raw or undercooked snails, slugs, or vegetables contaminated with larvae.⁷
• Drinking untreated water from lakes or rivers can also pose a risk.^8,9
• Activities like camping, hiking, or gardening in areas where the parasites or their hosts are prevalent increase the risk of contact with contaminated sources. Swimming in these environments, especially during warmer months, increases the risk of exposure. 
• Certain occupations, such as agriculture, wildlife management, or field research in endemic regions, can increase the risk of encountering parasitic hosts or vectors.
• Some populations are more vulnerable to parasitic meningitis, and people with weakened immune systems, such as those with HIV/AIDS, undergoing chemotherapy, or taking immunosuppressive drugs, are at higher risk of severe infections and complications.¹⁰
• People who travel to tropical or subtropical regions with a higher prevalence of parasitic infections are at increased risk. This includes tourists, business travellers, and those visiting friends or family in endemic areas.

Medical evaluation and diagnosis

The initial step in diagnosing parasitic meningitis involves a detailed clinical assessment, focusing on the patient's medical history, symptoms, and risk factors. Some tests used to diagnose meningitis are as follows,

• Nasal or throat swab, using a soft-tipped stick to take samples from the nose or throat. A lab will test your sample for signs of infection. 
• Lumbar puncture for cerebrospinal fluid (CSF) is the primary diagnostic tool for PAM, whereas tissue diagnostic is essential for GAE.¹ It involves collecting cerebrospinal fluid for analysis, which can provide valuable information about the underlying cause of meningitis. 
• Serological tests are used to detect antibodies or antigens associated with specific parasitic infections. Blood tests for antibodies against common parasitic infections, such as Toxoplasma gondii or Schistosoma spp., can help confirm a diagnosis. In some instances, additional tests like enzyme-linked immunosorbent assays (ELISA) or Western blotting are used to detect specific parasitic antigens or proteins.¹²
• Imaging studies help assess the extent of CNS involvement and identify any structural abnormalities or complications. CT scans can reveal signs of increased intracranial pressure, hydrocephalus, or other structural changes in the brain. MRI provides more detailed images of the brain and spinal cord, helping identify areas of inflammation, oedema, or other abnormalities.

Management and supportive measures

Pharmacological treatment is a cornerstone of managing parasitic meningitis, with antiparasitic medications and anti-inflammatory drugs forming the basis of therapy. The choice of medications depends on the identified parasite and the severity of the infection. For example, Angiostrongylus cantonensis (rat lungworm) is treated with medications like albendazole and ivermectin are commonly used, though evidence of their efficacy is variable.¹³ For Baylisascaris procyonis, albendazole is the primary treatment, often combined with corticosteroids to reduce inflammation caused by larval migration.¹⁴

Symptom management is crucial to alleviate discomfort and prevent complications. Non-steroidal anti-inflammatory drugs (NSAIDs) and other analgesics help control headaches and pain. Anticonvulsants, such as phenytoin or levetiracetam, are used to manage seizures, which are common in severe cases of parasitic meningitis. Antipyretics like acetaminophen can help manage fever and reduce discomfort. Adequate hydration, nutrition, and monitoring of vital signs are essential components of supportive care during treatment.

Follow-up and preventive strategies 

After the initial treatment phase, ongoing care and monitoring are necessary to ensure complete recovery and address any long-term complications. Physical therapy, occupational therapy, and speech therapy may be needed for patients with neurological deficits or motor impairments. Periodic CT or MRI scans can help track the resolution of inflammation and detect any persistent abnormalities. Neurological assessments help evaluate recovery progress.

Preventive strategies focus on reducing the risk of exposure to the parasites known to cause meningitis in adults. Proper handling, and thorough washing of fruits and vegetables, especially when traveling to regions with known parasitic risks, is crucial. Avoid swimming in warm freshwater lakes, rivers, or hot springs known to harbour parasites. Individuals working in agriculture, wildlife management, or field research in endemic regions should use protective clothing, gloves, and other safety equipment to minimize contact with parasites or their vectors. 

The prognosis and long-term outcomes for adults with parasitic meningitis can vary considerably, with some individuals experiencing significant recovery and others facing lasting complications. Early diagnosis and prompt treatment are critical for improving outcomes and reducing the risk of severe long-term effects. Comprehensive rehabilitation and support are essential to help individuals regain functionality and achieve the best possible quality of life.

FAQs

Is parasitic meningitis common?

Parasitic meningitis is much less common than viral and bacterial meningitis. 

How long does parasitic meningitis last?

Parasitic meningitis can progress rapidly, and usually over the course of 1 to 12 days. Almost fatal in almost all cases.

What is the survival rate for parasitic meningitis?

Parasitic infection is almost invariably fatal, with a mortality rate of 95%, which usually occurs within 72 hours from the onset of symptoms. 

Is parasitic meningitis curable?

There is no specific treatment, medications may be used to reduce the body's reaction rather than for the infection itself.