A seemingly harmless encounter with contaminated soil or undercooked meat can lead to a complex, sometimes life-threatening parasitic condition. Visceral larva migrans (VLM) is a condition that occurs when roundworm larvae are accidentally ingested and move through human organs, leaving in their path a range of different symptoms. The clinical manifestations of VLM vary depending on the location that the worms migrate to in the body. Common symptoms include fatigue, fever, abdominal pain and coughing. 

Want to know more about how VLM can present itself clinically? Read more to discover more about the condition and its symptoms and dangers. 

Introduction

Visceral larva migrans is in itself a clinical presentation of diseases like toxocariasis. It is a zoonotic disease (meaning that it originates in animals) caused by the ingestion of infective eggs and larvae of various species of roundworms. These worms can come from cats and dogs, as well as other domestic and wild animals such as ducks, foxes and chickens. Infection with these worms can present itself as visceral (about the organs) larva migrans (VLM) or ocular (about the eye) larva migrans (OLM). It is important to distinguish these from each other and from other parasitic diseases, to ensure her most accurate diagnosis and timely treatment of the disease. 

About VLM

VLM occurs when humans become the accidental hosts to several species of roundworms. When infected with VLM, worm larvae move through the host’s body into organs and cause several symptoms. 

Life cycle

VLM only occurs in humans accidentally. Typically, the Toxocara species of roundworms complete their life cycle inside of their intended hosts (like cats or dogs). For example, the life cycle of the Toxocara Canis (species of Toxocara that lives in dogs) follows these steps:

1. Roundworm eggs in the external environment develop into embryos and become capable of causing infection
2. These eggs are ingested by the host. This is either from the external environment or from infected meat
3. Eggs hatch and release larvae inside the body of the host. They move into the intestines and move through the intestinal wall. In younger dogs, the larvae can move into the lungs, get coughed up and reenter the small intestine. In older dogs, larvae can stay in body tissues, where they can be transferred to offspring if the dog is pregnant
4. The larvae mature in the small intestine and lay eggs
5. These eggs are passed out via the stool, enter the soil and the life cycle continues

Larva migration

Humans can get infected with the larva when they ingest the infective eggs. This can happen by:

• Accidentally ingesting infected faeces 
• Accidentally ingesting infected soil
• Ingesting contaminated meat that has not been cooked thoroughly 

Once the eggs have been ingested, they move to the small intestine. Once they mature, the larvae burrow out of the small intestine, where they move around the body. Because humans are accidental hosts to the parasites, there is no clear path of these worms to the organs. Hence, they distribute themselves relatively randomly but can make their way to the liver, lungs, muscles or even the heart. Here they can cause tissue damage and inflammation.¹

Immune response to the larva

Infection with the parasitic roundworms provokes an immune response in the tissues to which it has spread. Most notably, VLM causes eosinophilia.² This is when there is an excessive amount of disease-fighting white blood cells called eosinophils in the blood. 

Common clinical manifestations

The symptoms of VLM depend on where in the body the larvae have migrated to. Below are some possible symptoms of this condition. 

General Symptoms

General symptoms of VLM include:^3,4,5

• Fever
• Paleness
• Fatigue
• Night sweats 
• A general feeling of unwellness
• Joint and muscle pains

Gastrointestinal Symptoms

As the larvae mature in the small intestine, they can be responsible for gastrointestinal symptoms like:⁶

• Abdominal pain
• Blood in the stool
• Nausea
• Loss of appetite 

Respiratory Symptoms

If the larvae make their way to the lungs, they cause inflammation and pulmonary symptoms. These include:⁵

• Coughing
• Wheezing
• Shortness of breath
• Asthma-like symptoms
• Sounds during breathing (called rales and rhonchi)
• Pneumonitis - the swelling or inflammation of the lung without infection

Neurological Symptoms

Neurological clinical manifestations of VLM are rare but very serious. These symptoms indicate that the larvae have spread to the brain, where they can cause life-changing or life-threatening neurological symptoms, such as:^5,7,8

• Seizures
• Headaches
• Eosinophilia meningitis - infection of the membrane that surrounds the brain
• Changes in behaviour - for example, irritability

Dermatological Symptoms

The immune response that follows VLM may cause some dermatological symptoms like:⁵

• Rash
• Itching 

Other symptoms

Other symptoms are associated with the location to which the larvae migrated in the body. These include:^5,9

• Swelling of the liver (hepatomegaly)
• Hypereosinophilia - a severe increase in eosinophil white blood cells in the blood
• Hypergammaglobulinemia - overproduction of antibodies
• Myocarditis - inflammation of the heart

Severe and rare manifestations

The severity of the clinical manifestations of VLM depends on the amount of parasite ingested and where they migrated to in the body. Cases of the parasite infecting the brain or heart are severe and can be life-threatening but are also extremely rare. 

Risk factors and susceptible populations

There are certain aspects which make an individual more likely to contract VLM. These risk factors, in conjunction with the clinical manifestations, can help in the diagnosis of the condition. 

Geographical and environmental factors

VLM is present worldwide. Diseases such as toxocariasis that cause this condition occur mostly in developing countries. The distribution of this disease in developed countries indicates that infection is more common in those of a lower socioeconomic background. 

Risk factors

• Age - Children are more at risk than adults
• Owning a cat or dog - Larvae most commonly infect puppies
• Living on/ working in an area with highly contaminated soil
• Geophagy - The ingestion of clay soil (for example chalk) 
• Having pica
• Lack of education on the condition
• Poor sanitation and hygiene practice
• Living in a crowded environment 

Diagnostic approach

When diagnosing patients with VLM, practitioners must consider medical history and background, blood tests and imaging studies to detect the extent of damage. 

Laboratory tests

Firstly, the doctor may order a blood test called a full blood count to check the levels of eosinophils in the blood. A high eosinophil count would suggest that there is an immune response that is a result of parasite infection or allergy. To confirm, the doctor might order an ELISA test. 

Imaging techniques

Imaging techniques may be used to visualise the extent of damage or the location of the larvae. These include:¹²

• Ultrasound
• Contrast enhanced ultrasound
• Contrast enhanced computed tomography (CT)
• Contrast enhanced magnetic resonance imaging (MRI)
• Positron emission tomography (PET)

Management and treatment

Because humans are accidental hosts to the parasites, in the majority of cases the worms die inside the body without causing symptoms. Treatment for VLM consists of killing the worms that cause symptoms with antiparasitic medicines. Supporting treatments include anti-inflammatory treatments or treatments to manage the damage done by the condition. 

Summary

VLM is a zoonotic condition caused by the ingestion of roundworm eggs and larvae. When the larvae hatch, they migrate throughout the body and cause inflammation and damage to organs and tissues. This leads to a range of broad symptoms like fever and fatigue but also organ-specific symptoms like abdominal pains, respiratory issues, liver problems or in severe cases neurological or cardiac symptoms. Children, those who are in frequent contact with animals (cats, dogs or wild animals) and those who live in environments with highly contaminated soil are at highest risk of contracting this condition. 

Diagnosis involves evaluating medical history, taking blood tests and utilising imaging techniques to assess the extent of damage. Treatment includes antiparasitic medications and supportive therapies to help with the recovery of damaged organs and tissues. Understanding the clinical manifestations and risk factors associated with VLM is crucial for early diagnosis and correct treatment.