What is Tropical Pulmonary Eosinophilia?
Tropical Pulmonary Eosinophilia (TPE) is a strong lung reaction to tiny worms called microfilariae that get stuck in the lung tissue. TPE is a symptom of lymphatic filariasis, a disease caused by different types of thread-like worms called filarial nematodes. The term “Tropical Pulmonary Eosinophilia” was first used by Weingarten in 1943, but before that, it was referred to as “pseudotuberculosis with eosinophilia.”
TPE starts slowly and the main symptoms are fever, night-time cough, difficulty breathing, and wheezing. It’s common in regions where filarial worms are widespread, but it’s been appearing more often in developed countries due to people moving around and global interactions. Lymphatic filariasis is a neglected tropical disease. Its most common symptom is a condition called elephantiasis, which causes parts of the body to swell severely. The World Health Organization (WHO) estimates that about 120 million people in tropical and subtropical areas are infected with lymphatic filariasis. Studies show that less than 1% of people with filarial infestation will develop TPE.
Diseases involving a high number of a type of white blood cells called eosinophils in the lungs can be divided into two types based on what causes them: extrinsic, from outside factors, and intrinsic, from the body itself. The external causes include certain medications (like sulfonamides, phenytoin, phenobarbital, and carbamazepine) and infectious agents (like parasites, fungi, and a type of bacterium known as mycobacteria). The intrinsic causes, on the other hand, include conditions like Churg-Strauss syndrome, eosinophilic granuloma, chronic eosinophilic pneumonia, and idiopathic hypereosinophilic syndrome. The disease we’re talking about, Tropical Pulmonary Eosinophilia, falls under the extrinsic causes category.
What Causes Tropical Pulmonary Eosinophilia?
Tropical Pulmonary Eosinophilia (TPE) is a particular kind of allergic reaction to tiny worms called microfilariae that sometimes get trapped in the lungs. This condition is caused by specific types of roundworms, namely Wuchereria bancrofti, Brugia malayi, and Brugia timori, that normally live in our lymphatic system and bloodstream, these systems are involved in immune function and circulation, respectively.
Filariasis, the disease these roundworms cause, is spread through mosquito bites. Essentially, when a mosquito carrying these worms bites a person, it can transmit the disease. Particularly, the mosquitos spreading W. bancrofti are species like Culex, Anopheles, and Aedes. So, they act as a carrier or ‘vector’ for the disease.
Risk Factors and Frequency for Tropical Pulmonary Eosinophilia
Tropical pulmonary eosinophilia, or TPE, is a disease commonly found in tropical areas. However, it is especially common in areas with high rates of worm infections, such as the Indian subcontinent, Southeast Asia, South America, and Africa. But due to more people traveling and migrating between these areas and Western countries, the disease is also becoming more common in the West.
- People who travel to these high-risk areas are more likely to catch TPE than those who live there permanently. This is because residents often develop immunity to the worm infections that cause TPE.
- TPE is between 4 and 7 times more common in males than in females.
- The disease most commonly affects young adults.
- People with weakened immune systems are usually hit harder by the infection.
Signs and Symptoms of Tropical Pulmonary Eosinophilia
The patient’s past, including their living or travel history to areas known for filarial infections, is important in diagnosing the disease. Other factors like their food habits and medication usage can help rule out other diseases which also cause an increase in eosinophils (a type of white blood cells) in the lungs. Loeffler syndrome, which shows similar symptoms, can be caused by infections, certain foods, or medication.
Tropical pulmonary eosinophilia, another disease that causes lung eosinophilia, has several characteristic symptoms, including:
- Dry cough that comes and goes, often worse at night
- Coughing accompanied by difficulty breathing
- General unwell feeling, high temperature, loss of appetite, and weight loss
- High eosinophil count in blood, more than 3,000/mm3
- Slightly enlarged liver or spleen and swollen lymph nodes (seen only in some cases)
Physical check-up may also reveal abnormalities, such as:
- Unusual breath sounds like wheezing and crackling when listening to the chest
- Slightly enlarged organs felt during abdomen check-up (only in a few cases)
- Swollen lymph nodes
Testing for Tropical Pulmonary Eosinophilia
If your doctor suspects you have a condition called tropical pulmonary eosinophilia (TPE), they will use various tests to confirm this. These include blood tests, stool tests, chest x-rays, and breathing tests.
For the blood test, usually known as a complete blood count, they will look for an increased number of white blood cells, which can signal an inflammation or infection in the body. They will be specifically looking for a type of white blood cell known as eosinophils. If your eosinophil count is higher than 3,000 per cubic millimeter of blood, this is a key sign of TPE.
In a stool test, they will examine your stool under a microscope to rule out any other parasites that might cause similar symptoms to TPE.
They might also measure your immunoglobulin E level – this is a type of protein in your blood that’s linked to allergic responses. In TPE, this level is often elevated.
Another possible blood test is an indirect ELISA test. This looks for antibodies – proteins your body creates to fight off harmful substances – that specifically target filarial parasites which causes TPE.
Imaging tests, like a chest x-ray, can also be used to check for signs of TPE. These signs might look like splotches or specks (opacities) scattered across your lungs, or even small areas that look a lot like tiny freckles (miliary mottling). But it’s worth noting that up to 30% of people with TPE may have lungs that look normal on an x-ray. In more advanced cases, scarring (fibrosis) may be visible.
In cases where the doctors are still uncertain about the diagnosis, a CT scan might be performed, which might show issues like bronchiectasis (damaged and enlarged airways), swollen lymph nodes (lymphadenopathy), or fluid around the lungs (pleural effusion).
Finally, your doctor might ask you to perform a pulmonary function test. This checks how well your lungs are working and could reveal a mixed pattern with predominantly restrictive (difficulty fully expanding the lungs) and mildly to moderately obstructive (difficulty in breathing out) pattern.
Do note that TPE can sometimes be confused with other conditions that cause similar symptoms. Therefore, it might be necessary to perform additional tests to confirm the diagnosis.
To diagnose TPE, doctors generally look for a combination of specific signs: a history of living in or traveling to regions known for filarial infections; coughing fits and shortness of breath especially at night; high levels of eosinophils and Immunoglobulin E in your blood; detection of filarial antibodies; visible signs in your chest x-ray; and your symptoms improve significantly after medication with Diethylcarbamazine (DEC), which is a specialized treatment for TPE.
Treatment Options for Tropical Pulmonary Eosinophilia
Tropical pulmonary eosinophilia, a type of lung infection, is generally treated with a medication known as diethylcarbamazine or DEC for 21 days. DEC is effective against both the young (microfilariae) and adult forms of the infection. A noticeable improvement in the symptoms can be seen with DEC, which is a defining feature of this condition.
Alongside DEC, corticosteroids, another type of medication, can also be used to lessen inflammation in the airways over time. It’s believed that some cells in the lower part of the respiratory tract release certain harmful substances which cause long-term inflammation and mild lung damage. Corticosteroids can help reduce this inflammation and damage.
However, before starting corticosteroids, it’s important to ensure that there’s no existing lung infection called strongyloidiasis, because corticosteroids could potentially cause this infection to spread throughout the body.
Other medications such as ivermectin (which works on the young microfilariae), and albendazole (which works on adult worms), can also be used. However, there is no published data available about their effectiveness.
What else can Tropical Pulmonary Eosinophilia be?
People who suffer from pulmonary eosinophilia, a condition where there is a high number of white blood cells called eosinophils in the lungs, may also encounter other illnesses, such as:
- Other infections like Strongyloides, Toxocara, and Ascariasis
- Bronchial asthma
- Allergic bronchopulmonary aspergillosis
- Allergic rhinitis – an allergic reaction causing a runny nose
- Acute and chronic eosinophilic pneumonia – an infection of the lungs
- Fungal pneumonia – a type of pneumonia caused by a fungus
- Churg-Strauss syndrome – a disease that causes blood vessels to become inflamed
- DRESS syndrome – a severe reaction to a drug that includes eosinophilia and systemic symptoms
- Miliary tuberculosis – a serious type of tuberculosis that can affect the entire body
What to expect with Tropical Pulmonary Eosinophilia
Most patients have shown a positive outcome after being treated with DEC. However, in some instances, mild interstitial lung disease, which is a type of lung condition known to cause inflammation, has been found to continue even after the treatment. Research also indicates that about 20% of patients may experience a relapse in their condition within five years.
Patients who develop pulmonary hypertension— a condition characterized by high blood pressure in the arteries of the lungs—may have a challenging road ahead. This is because, unfortunately, once this condition sets in, it is often irreversible, leading to a poorer health outlook.
Possible Complications When Diagnosed with Tropical Pulmonary Eosinophilia
If Tropical Pulmonary Eosinophilia (TPE) isn’t treated in time or isn’t treated at all, it can result in serious lung conditions. These conditions include lung fibrosis, which is the scarring of the lungs, or chronic bronchitis causing long-term respiratory failure.
In some cases, patients can experience high blood pressure in the lungs, also known as “pulmonary hypertension.” This situation could lead to “cor-pulmonale,” a condition where the right side of the heart becomes enlarged. This typically happens because fragmented microfilariae (small worms) can potentially block the small blood vessels in the lungs.
Common Risk Factors:
- Untreated or late-treated Tropical Pulmonary Eosinophilia (TPE)
- Lung fibrosis
- Chronic bronchitis
- Chronic respiratory failure
- Pulmonary hypertension
- Cor-pulmonale
- Embolization of destructed microfilariae into lung capillaries
Preventing Tropical Pulmonary Eosinophilia
If you’re planning on traveling to areas where Filariasis is commonly found, such as India, South East Asia, South America, and Africa, it’s crucial to take necessary precautions to prevent mosquito bites. Filariasis, a disease spread through mosquito bites, can be transmitted from one person to another. Mosquitos are the carrier or ‘vector’ for this disease. For protection against mosquitos, travelers are advised to use methods like bed nets treated with insecticides and clothing treated with a mosquito-repelling chemical called permethrin.
