Parasite, Eosinophilic Meningitis / Rat lung worm

Eosinophilic meningitis is an infection of the brain occurring in association with an increase in the number of eosinophils. The organism most commonly causing eosinophilic meningitis is a rat lung worm called angiostrongylus cantonensis. Other worm infections that can cause a similar picture include paragonimiasis, gnathostomiasis and schistosomiasis.

Angiostrongylus is a worm of around 20 mm in length, which lives in the pulmonary artery in the rat, hence its name rat lung worm. Adult worms lay eggs in the arteries which hatch into first stage larvae. These larvae penetrate the artery wall to enter the lungs and migrate up the windpipe and into the gut and are expelled in the feces of the rodent. Once outside the body, they survive in damp conditions and penetrate the skin of snails and slugs. Snails and slugs can also become infected by eating rodent feces containing the larvae. There follows a further development stage within the snails and slugs. Infection is spread back to the rat when rats eat snails and slugs, and larvae in the tissues of these mollusks penetrate through the gut wall into the circulation and reach the rat brain. In the rat brain the larvae develop further, and when mature migrate through the rat body to the pulmonary artery where they mature to an adult worm.

In this complicated life cycle, humans become infected by accident when they eat an infected snail, or food that has been contaminated by slugs or snails, particularly SALADS. In the intestines the larvae penetrate the lining and migrate to the brain, spinal cord and eye. There they attempt to develop into final stage larvae but are generally unable to do this because development can only occur in rats. The larvae gather on the surface of the brain and spinal cord, causing intense inflammation. Very occasionally a larva will reach maturity and become an adult worm in the lung.

Angiostrongylus is found predominantly in south-east Asia, particularly Thailand and the Pacific Islands. It is a rare infection in travelers. It turns out to be more common than thought even in Hawaii.

Mollusks intended for human consumption should be cooked thoroughly, or frozen for 12 hours to kill the larvae. Mollusk numbers should be controlled in food growing areas. Measures should be taken to eradicate rodents near human habitations and farming areas.

The severity of eosinophilic meningitis varies widely depending on the number of larvae present. The infection is generally benign and self-limiting, but can be severe with neurological complications or even death. Symptoms reach their peak around 2 weeks after onset, but tend to settle after another 2 weeks at the most.

The diagnosis is made based on clinical features, a knowledge of whether the area is high risk for this infection, abnormalities on examination of cerebrospinal fluid from a lumbar puncture and scanning of the head. Larvae can sometimes be found in cerebrospinal fluid or in the eye. Both blood and cerebrospinal fluid have elevated levels of eosinophils. Antibody tests may be of benefit.

In many patients the infection is mild and as mentioned above tends to resolve within a month. The mortality rate is low, around 2 to 3%. However patients who develop weakness or blindness as a result of eosinophilic meningitis are unlikely to regain power or their sight.

 


Signs, symptoms & indicators of Parasite, Eosinophilic Meningitis / Rat lung worm

Lab Values - Cells  

(Slightly/highly) elevated eosinophil count



Symptoms - Gas-Int - General  

Unexplained nausea

Patients may develop nausea and vomiting and abdominal pain shortly after eating suspect food.



Symptoms - General  

General weakness

In severe cases patients develop changes in their sensation and weakness of the limbs.



Symptoms - Head - Eyes/Ocular  

Vision disturbances

Up to 10% of individuals have involvement of the eyes and blindness occurs occasionally.



Symptoms - Muscular  

Having recent neck stiffness



Symptoms - Respiratory  

Recent productive cough

If adult worms reach the lungs, patients may have a cough with sputum, crackles on listening to the chest and abnormalities of the chest X-ray.




Conditions that suggest Parasite, Eosinophilic Meningitis / Rat lung worm

Metabolic  

Headaches, Migraine/Tension

After an incubation period of around 2 weeks headache develops either suddenly or insidiously, with nausea, vomiting and neck stiffness.




Recommendations for Parasite, Eosinophilic Meningitis / Rat lung worm

Drug  

Conventional Drugs / Information

In severe cases steroids may help to reduce inflammation and symptoms. The worms generally die without treatment after a few weeks. Giving a patient anti-worm treatment can make their condition much worse by killing all worms present at the same time which results in even greater brain inflammation.



Key

Weak or unproven link
Strong or generally accepted link
Likely to help

Glossary

Eosinophil

The eosinophils, ordinarily about 2% of the granulocyte count (60 to 75% of the white blood cells), increase in number in the presence of allergic disorders and parasitic infestations.

Millimeter

(mm): A metric unit of length equaling one thousandth of a meter, or one tenth of a centimeter. There are 25.4 millimeters in one inch.

Pulmonary

Pertaining to the lungs.

Benign

Literally: innocent; not malignant. Often used to refer to cells that are not cancerous.

Antibody

A type of serum protein (globulin) synthesized by white blood cells of the lymphoid type in response to an antigenic (foreign substance) stimulus. Antibodies are complex substances formed to neutralize or destroy these antigens in the blood. Antibody activity normally fights infection but can be damaging in allergies and a group of diseases that are called autoimmune diseases.

Nausea

Symptoms resulting from an inclination to vomit.

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