Diagnosis of Rat Lungworm Disease
The diagnosis of disease caused by Angiostrongylus cantonensis infestation is quite often difficult and relies to a large extent on the history of a likely ingestion or consumption of a commonly infested host and the presence of typical features of the disease. The presumed diagnosis is particularly likely when eosinophilic meningoencephalitis can be confirmed. The diagnosis of eosinophilic meningitis can be arrived at through detection of elevated cranial pressure and increased numbers of eosinophils. The diagnosis of the cause of eosinophilic meningitis and the presence of Angiostrongylus cantonensis is remarkably more difficult.
Many tests are unreliable
A spinal tap, or a sample of CSF, must be taken to search for Angiostrongylus cantonensis worms or larvae. Angiostrongylus cantonensis is undetectable in the CSF of more than half of the infected individuals. Current methods of detecting specific antigens associated with Angiostrongylus cantonensis are also unreliable. Consequently, alternative approaches to detect antigen-antibody reactions are being explored, such as Immuno-PCR. A rapid dot-blot ELISA test is also available for quick, effective and economical on-site diagnosis of Angiostrongylus cantonensis.
The severity and clinical course of Angiostrongylus cantonensis disease depends significantly on the ingested load of third-stage larvae, creating great variability from case to case which makes clinical trials difficult to design and effectiveness of treatments difficult to discern.
Typical conservative medical management including analgesics and sedatives provide minimal relief for the headaches and hyperesthesias. Removing cerebrospinal fluid at regular three-to-seven-day intervals is the only proven method of significantly reducing intracranial pressure and can be used for symptomatic treatment of headaches. This process may be repeated until improvement is shown.
Some possible solutions
There is growing evidence of moderate quality that suggests corticosteroid therapy using prednisolone or dexamethasone has beneficial effect in treating the CNS symptoms related to Angiostrongylus cantonensis infections. Although early research did not show treatment with antihelminthic agents (parasite killing drugs) like thiobendazole or albendazole effective in improving the clinical course of the illness, a number or recent studies out of Thailand and China show that the combination of glucocorticoids and antihelminthics are safe and decrease the duration of headaches.
Although the addition of antihelminthic agents for management of Angiostrongylus cantonensis infection has a theoretic risk of precipitating a neurologic crisis by releasing an overwhelming load of antigens though simultaneous death of the larvae, no study has shown this to exist in the clinical setting.
In addition, the failure to kill parasites before they attempt to migrate out of the CNS increases the risk of mechanical damage by migrating larvae. Although combination therapy using albendazole and prednisolone has no significant advantage compared to treatment using prednisolone alone in mild cases, the treatment with antihelminthics is demonstrably safe and may have significant benefit for patients with high parasite loads at risk for permanent disability or death.
More Research needed
Further studies to better define treatment regimens for mild, moderate, and severe disease would be extremely useful but have not yet been performed due to the technical difficulties mentioned above.
If you would like to help further research in Rat Lungworm Disease by making a donation - see the Research support page by clicking here
The incubation period of the species in humans is between 1 to 4 weeks on average, after infection. In humans, symptoms show up after a week or a month upon consuming the infectious meal.
The below table lists the symptoms and their relative frequencies:
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No.
|
Symptoms
|
Relative frequency
|
|
1
|
Headache
|
100%
|
|
2
|
Photophobia
-sensitivity or discomfort of the eyes when exposed to light
|
92%
|
|
3
|
Neck stiffness and fatigue
|
83%
|
|
4
|
Hyperesthesia
-heightened sensitivity to pain or touch
|
75%
|
|
5
|
Vomiting
|
67%
|
|
6
|
Paresthesias
-odd sensation from the skin such as tingling, tickling, pricking, numbness or burning without an external source
|
50%
|
Preliminary Guidelines for the Diagnosis and Treatment of Human Neuroangiostrongyliasis (Rat Lungworm Disease) in Hawaii
The Clinical Subcommittee of the Hawaii Governor’s Joint Task Force on Rat Lungworm Disease has published its report, “Preliminary Guidelines for the Diagnosis and Treatment of Human Neuroangiostrongyliasis (Rat Lungworm Disease) in Hawaii”. The full document can be read here; below are the key points of the report.
Clinicians in Hawaii should have a high index of suspicion for neuroangiostrongyliasis.
Suspect cases should be discussed with the Department of Health (DOH) Disease Investigation Branch (DIB) at the earliest opportunity to facilitate prompt, accurate diagnosis and appropriate patient management. Call (808) 586-4586 for the Disease Reporting Line.
Typical symptoms in adults include severe headaches, neck stiffness, nausea, paresthesias, and limb pains. Highly suggestive symptoms include migratory hyperesthesias, cranial nerve abnormalities, ataxia, and focal neurologic findings which are migratory or do not follow a dermatomal distribution.
Typical symptoms in children include fever, abdominal pain, vomiting, irritability, poor appetite, muscle weakness, fatigue, and lethargy.
Lumbar puncture (LP) is an essential part of the evaluation of suspected neuroangiostrongyliasis. It is a low-risk procedure and has therapeutic benefits, including relief of headaches, nausea, and vomiting.
A presumptive diagnosis of neuroangiostrongyliasis requires all three of the following:
A history of suggestive symptoms and signs,
Evidence of eosinophilic meningitis in the cerebrospinal fluid (CSF), and
An exposure history, which includes residence in or recent travel to an endemic area.
Eosinophilic meningitis is the hallmark of the disease and is defined as the presence of 10 or more eosinophils per μL of CSF and/or eosinophils accounting for more than 10% of CSF white blood cells when there are at least 6 total WBC per μL in CSF.
CSF eosinophil counts may be absent or low early in the course of the disease, requiring repeat LPs if neuroangiostrongyliasis is still suspected.
Real-time polymerase chain reaction (RTi-PCR) of CSF for A. cantonensis DNA is the best way to confirm the infection and is available in Hawaii through the DIB or from the Centers for Disease Control and Prevention (CDC) for the rest of the United States.
CSF RTi-PCR may be negative in the early stages of infection.
Repeat LP and testing is indicated if neuroangiostrongyliasis is still suspected.
Baseline studies should include a complete blood count (CBC) with differential, serum electrolytes, liver function tests, renal function tests, blood glucose, urinalysis, and chest x-ray.
Peripheral eosinophil counts of ≥ 500 cells/μL are often present during the course of the illness but may be absent.
Magnetic resonance imaging (MRI) of the brain, although not required, may be helpful in diagnosing suspected neuroangiostrongyliasis. Focused MRI of the spine may be appropriate if indicated by clinical presentation.
Serological tests for antibodies against A. cantonensis in the serum or CSF are not recommended for the diagnosis of neuroangiostrongyliasis.
High dose corticosteroids have been shown to improve clinical outcomes. Start corticosteroids as soon as a presumptive diagnosis of neuroangiostrongyliasis is made and assuming no contraindications.
Individuals with diabetes or glucose intolerance should be closely monitored.
Modifications to the patient’s diabetes medications may be needed.
The addition of albendazole, an anthelminthic drug, may provide additional benefits, although there is limited evidence of this in humans.
If albendazole is used, combine with corticosteroids to blunt any possible increase in the inflammatory response to dying worms.
Careful clinical monitoring is recommended in all patients, and specialist consultation (e.g., infectious disease, neurology, etc.) may be advisable.
Pain management may require early consultation with a pain specialist.
Reporting
HDOH requires that clinicians report patients with eosinophilic meningitis, i.e., signs and/or symptoms consistent with meningitis plus eosinophils in the cerebrospinal fluid (CSF) without possible alternative causes, including CNS infection with other microbes, reaction to foreign material in the CNS (e.g., intracranial hardware or myelography dye), medications (e.g., intrathecal vancomycin or gentamicin), neoplasms, multiple sclerosis, and neurosarcoidosis by calling (808) 586-4586.
Resources for Clinicians
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