Visceral Larva Migrans: Symptoms, Types, Causes and Treatment

Visceral Larva Migrans (VLM) is a fascinating and sometimes overlooked parasitic disease that bridges the world of veterinary and human medicine. Most commonly caused by the migration of animal roundworm larvae through human tissues, VLM can present with a range of symptoms, often making it a diagnostic challenge. Understanding the symptoms, types, causes, and treatment options for VLM is crucial for clinicians, caregivers, and anyone interested in infectious diseases.

Symptoms of Visceral Larva Migrans

Recognizing the symptoms of Visceral Larva Migrans can be challenging, as its signs often mimic those of more common illnesses. However, understanding its characteristic features can aid in early identification and treatment, especially in children and at-risk adults.

Symptom	Typical Patient	Common Organs Affected	Source(s)
Eosinophilia	Children, adults	Blood, liver	1 2 5 8
Hepatomegaly	Children	Liver	1 2 8 14
Fever	Preschoolers, adults	Systemic	2 8
Pulmonary	Children, adults	Lungs	2 11 14
Neurologic	Some children	CNS	2 6
Anemia	Children	Blood	2 14
Skin/Rash	Adults	Skin	3
Eye Complications	Children, adults	Eyes	7 14

Table 1: Key Symptoms of Visceral Larva Migrans

Classic Clinical Features

• Eosinophilia: Marked elevation in eosinophil count is a hallmark of VLM. This can be extreme, sometimes accompanied by overall white blood cell elevation (leukocytosis) 1 2 5 8.
• Hepatomegaly: Enlargement of the liver is commonly seen, particularly in young children, and may be the first clue noticed on physical exam or imaging 1 2 8 14.
• Fever and Malaise: Many patients present with low-grade persistent fever, irritability, and a general sense of being unwell 2 8.
• Pulmonary Symptoms: Cough, wheezing, and pulmonary infiltrates may develop due to larvae migrating through the lungs 2 11 14.

Less Frequent Symptoms

• Neurologic Involvement: In rare cases, the central nervous system (CNS) may be affected, resulting in convulsions, headaches, or even fatal meningoencephalitis 2 6.
• Anemia and Poor Weight Gain: Especially in children, chronic blood loss or inflammation can lead to anemia, fatigue, and failure to thrive 2 14.
• Skin Manifestations: Pruritus and rash, more commonly seen in adults, reflect allergic inflammation 3.
• Eye Involvement: Ocular larva migrans, while related, is a distinct syndrome but is important to consider due to the risk of vision loss 7 14.

Laboratory and Imaging Findings

• Hypergammaglobulinemia: Elevated immunoglobulins are frequently seen, indicating immune system activation 2 8.
• Imaging: Liver imaging may reveal abscess-like lesions. Pulmonary infiltrates are sometimes seen on chest X-rays 11 16.

Types of Visceral Larva Migrans

Visceral Larva Migrans is not a single disease but encompasses several clinical syndromes depending on the location and extent of larval migration. Recognizing these types is essential for proper management and prognosis.

Type	Main Features	Typical Age Group	Source(s)
Classical/Visceral	Systemic symptoms, hepatomegaly, eosinophilia	Children	1 2 7 8
Ocular	Visual loss, eye granuloma, minimal systemic signs	Children/adults	7 14
Covert	Mild, non-specific symptoms	Children/adults	13
Neurologic	CNS involvement, seizures	Children/adults	2 6
Hepatic	Liver abscess, granulomatous lesions	Children/adults	1 16

Table 2: Types of Visceral Larva Migrans

Classical (Systemic) VLM

• Definition: The most well-known form; involves migration of larvae through various organs, most notably the liver and lungs.
• Presentation: Fever, hepatomegaly, marked eosinophilia, anemia, and pulmonary symptoms 1 2 8.

Ocular Larva Migrans

• Definition: A distinct entity where larvae localize in the eye, often without systemic symptoms 7.
• Key Features: Visual disturbances, retinal granuloma, potential for misdiagnosis as retinoblastoma, risk of blindness if untreated 7 14.

Covert Toxocariasis

• Definition: A milder, more subtle form with vague symptoms such as abdominal pain, irritability, and mild eosinophilia 13.
• Importance: May be overlooked; important in seroprevalence studies.

Neurologic VLM

• Definition: Rare but severe involvement of the CNS, including meningoencephalitis and seizures 2 6.
• Clinical Impact: Can be fatal; often associated with raccoon roundworm infection (Baylisascaris procyonis) in the U.S. 6.

Hepatic VLM

• Definition: Dominant liver involvement, sometimes presenting as abscesses or granulomas 1 16.
• Imaging: May show persistent lesions even after clinical recovery 16.

Causes of Visceral Larva Migrans

VLM is fundamentally a zoonotic disease—humans become accidental hosts for larval nematodes that normally infect animals. Understanding how and why these infections occur is vital for prevention and control.

Cause	Main Source	Transmission Route	Source(s)
Toxocara canis	Dogs (esp. puppies)	Ingesting contaminated soil/food	1 4 5 8 14
Toxocara cati	Cats	Ingesting contaminated soil/food	1 5
Baylisascaris procyonis	Raccoons	Ingesting contaminated soil/food	6
Dietary Exposure	Undercooked animal meat	Ingesting larvae in meat	11
Environmental	Poor sanitation, pet ownership	Direct/indirect contact	3 4 8

Table 3: Main Causes of Visceral Larva Migrans

The Culprit Parasites

• Toxocara canis: The dog roundworm is the principal cause of VLM, especially in children who come into contact with contaminated soil via geophagia (pica) or poor hand hygiene 1 4 5 8 14.
• Toxocara cati: The cat roundworm can also be a cause, though less frequently 1 5.
• Baylisascaris procyonis: The raccoon roundworm is a more dangerous but rarer cause, notorious for causing severe neurologic disease 6.

Transmission Pathways

• Soil Contamination: Eggs are shed in the feces of infected animals. Children are at risk through play and hand-to-mouth behavior 4 8.
• Foodborne: Consumption of undercooked meat, such as chicken livers, has been reported as a rare route 11.
• Environmental and Societal Factors: Living in rural areas, owning multiple dogs, hunting, and poor sanitation increase risk 3 4.

Host-Parasite Interaction

• Accidental Host: Humans are not the intended host. Larvae cannot complete their lifecycle in humans, so they wander through tissues, causing inflammation and allergic reactions 1 8 9.
• Immune Response: The migration and death of larvae trigger eosinophilia and other immune reactions, leading to the clinical features of VLM 1 2 8.

Treatment of Visceral Larva Migrans

While many cases of VLM resolve spontaneously, especially if exposure ceases, targeted treatment can accelerate recovery and prevent complications. Timely therapy is essential, especially in severe or organ-threatening cases.

Treatment	Indication	Effectiveness	Source(s)
Albendazole	First-line, all forms	High, preferred	12 13
Mebendazole	Alternative	Moderate	13
Diethylcarbamazine	Resistant cases	70-75% cure	13 14 15
Thiabendazole	Resistant/alternative	70% cure	12 13 15
Supportive Care	Mild/asymptomatic cases	Often sufficient	14
Corticosteroids	Severe inflammation (esp. CNS, eye)	Adjunctive	14
Prevention	Hygiene, pet deworming	Essential	4 8 14

Table 4: Treatment and Management Options

Antiparasitic Therapy

• Albendazole: Considered the drug of choice due to efficacy and tolerability. Typical course: 10 mg/kg daily for 5 days. Reduces eosinophilia and resolves symptoms in most patients 12 13.
• Mebendazole: Used as an alternative; less effective than albendazole 13.
• Diethylcarbamazine (DEC): Previously used, still effective especially in resistant cases. Cure rates of 70–75% reported 13 14 15.
• Thiabendazole: Another option, with cure rates similar to DEC (around 70%), but with more side effects 12 13 15.

Adjunctive and Supportive Care

• Corticosteroids: Indicated for severe organ involvement (e.g., CNS, ocular, myocarditis) to control inflammation 14.
• Supportive Measures: Many children recover spontaneously once exposure is stopped. Monitoring eosinophil counts and symptoms is important 14.

Monitoring and Follow-up

• Blood Counts: Decline in eosinophilia is a good marker of treatment response 16.
• Imaging: Liver and lung lesions may persist radiologically despite clinical improvement 16.
• Serology: ELISA (using Toxocara excretory-secretory antigens) is the most sensitive and specific diagnostic tool 4 10.

Prevention

• Hygiene and Education: Handwashing, discouraging pica, and supervising children’s play in areas where pets defecate are essential 4 8 14.
• Pet Care: Regular deworming of dogs and cats, especially puppies and kittens, reduces environmental contamination 4 8.
• Food Safety: Avoiding raw or undercooked meats, especially in regions where such exposures have been linked to VLM 11.

Conclusion

Visceral Larva Migrans is a complex, multisystem disease that highlights the close relationship between human and animal health. Awareness and early recognition are key to preventing complications, especially in children and vulnerable populations. Here’s a summary of the main points:

• VLM is most often caused by dog (Toxocara canis) and cat (Toxocara cati) roundworms, with rare cases from raccoon roundworm (Baylisascaris procyonis).
• Symptoms range from fever, hepatomegaly, and eosinophilia to pulmonary, neurologic, skin, and eye involvement.
• There are several clinical types: classical visceral, ocular, covert, neurologic, and hepatic.
• Diagnosis relies on clinical features, laboratory findings (eosinophilia, hypergammaglobulinemia), imaging, and serology (ELISA).
• Treatment is usually with albendazole; alternatives or adjuncts include mebendazole, diethylcarbamazine, thiabendazole, and corticosteroids.
• Prevention—through hygiene, pet care, and food safety—is the most effective control strategy.

By understanding the signs, causes, and treatments of Visceral Larva Migrans, we can better protect ourselves and our communities from this intriguing yet preventable disease.