Lungworms are parasitic worms that live in the lungs of various mammals. They can infect humans as well as other animals like cats, dogs, foxes, and badgers. Lungworm infections are found worldwide, but some regions see higher rates than others.
What are lungworms?
Lungworms are a type of roundworm parasite from the Nematoda phylum. There are several different genera of lungworms that can infect mammals:
- Aelurostrongylus – infects cats and other felines
- Angiostrongylus – infects rodents and other wild animals
- Capillaria – infects dogs, foxes, wolves, and bears
- Crenosoma – infects dogs and foxes
- Dictyocaulus – infects cattle and deer
- Metastrongylus – infects pigs
- Muellerius – infects sheep and goats
- Oslerus – infects dogs
- Parastrongylus – infects badgers
The most common lungworm genera that infect humans are:
- Ascaris
- Capillaria
- Paragonimus
- Strongyloides
- Toxocara
Lungworm larvae mature into adults which live in the respiratory system and lungs. They lay eggs which are passed out in the feces or coughed up. The eggs hatch into larvae in the environment, completing the parasite’s life cycle.
How are lungworms transmitted?
People and animals become infected with lungworms by ingesting larvae present in the environment. Common routes of transmission include:
- Eating contaminated soil – Geophagia (dirt eating) and eating unwashed produce can lead to ingestion of lungworm larvae.
- Drinking contaminated water – Larvae can be present in untreated water sources.
- Eating infected snails or slugs – Some lungworm larvae develop in snails and slugs as intermediate hosts.
- Skin penetration – Larvae of some species can penetrate the skin and migrate to the lungs.
In most cases, transmission occurs when eggs passed in feces contaminate soil, water, or vegetation. Animals and people are exposed when they have contact with this contaminated environment.
Where are lungworm infections most prevalent globally?
Lungworm infections have been reported all over the world. However, there are certain regions where lungworms are more endemic due to environmental conditions, animal reservoirs, and socioeconomic factors that promote transmission. Some of the places lungworm infections are most common include:
- Southeast Asia – Areas like Thailand and Laos have high rates of foodborne Paragonimus infections.
- Sub-Saharan Africa – Ascariasis and hookworm infections are widespread.
- Latin America – Toxocariasis, a zoonotic disease, is prevalent in poorer communities.
- Southern United States – Baylisascaris and cutaneous larva migrans infections have been reported.
- Middle East – Toxocariasis is common in rural areas.
In developing countries with tropical climates, lack of sanitation and access to clean water contribute to fecal-oral transmission of lungworms. Eating raw or undercooked meat and produce also leads to more infections in these regions.
Which lungworms are most common?
Some of the most common lungworm infections globally include:
Ascariasis
Caused by Ascaris lumbricoides, a large parasitic roundworm. It infects over 1 billion people worldwide, mostly in sub-Saharan Africa, China, East Asia, and South America. Ascaris eggs are transmitted through contaminated food and water sources. Symptoms include coughing, breathing problems, and nutritional deficiencies.
Hookworm
Caused by Ancylostoma duodenale and Necator americanus. Up to 740 million people may be infected globally. Hookworm is prevalent in moist, warm climates where sanitation is poor. Larvae penetrate bare skin and migrate to lungs before being coughed up and swallowed. Symptoms include cough, abdominal pain, rashes, and anemia.
Paragonimiasis
Caused by Paragonimus westermani parasites. Approximately 21 million people are infected, mostly in Asia, sub-Saharan Africa, and South America. Transmission occurs by eating raw or undercooked crab/crayfish. Symptoms include chronic cough, chest pain, bloody sputum, and fever.
Toxocariasis
Caused by Toxocara canis and T. cati worms. Common in tropical climate developing countries. people are infected by ingesting eggs shed in dog/cat feces from contaminated soil. Larvae migrate to lungs and other organs. Symptoms are usually mild but can include cough, fever, rash, eye disease.
Strongyloidiasis
Caused by Strongyloides stercoralis threadworms. Estimated 30-100 million people infected worldwide. Transmission occurs through skin contact with larvae in soil. Larvae migrate to lungs before being swallowed. Can cause long-lasting infections. Symptoms include abdominal pain, diarrhea, coughing, and skin rashes.
Where are lungworms most common in the United States?
In the U.S., lungworm prevalence varies by region and climate:
Southeast
The southern states of Louisiana, Mississippi, Alabama, Georgia and Florida have reports of Parelaphostrongylus tenuis meningeal worm infections in deer. This lungworm can spread to sheep, goats, and other livestock.
Mid-Atlantic
Angiostrongylus cantonensis rat lungworm is becoming more common in mollusks in states like North Carolina, South Carolina, Virginia, Maryland and Hawaii. It can cause meningitis in humans.
Northeast
Focal areas of baylisascariasis, caused by the raccoon roundworm Baylisascaris procyonis have been reported in states like New York, Pennsylvania, Massachusetts, and Connecticut. Children are most at risk of severe infection.
Midwest
Parelaphostrongylus tenuis is also found in Midwestern states with white-tailed deer populations like Iowa, Missouri, Illinois, and Indiana. It can spread to grazing livestock.
West
The lungworm Eucoleus aerophilus infects wild foxes and has spread to pet dogs in some Western states like California, Washington, and Oregon. It can cause bronchopneumonia.
Southwest
Cases of cutaneous larva migrans, caused by dog and cat hookworm larvae, have been reported in southwestern states like New Mexico, Arizona, Texas, and California. Transmission is through skin contact with larvae.
Which animals are most affected by lungworms?
Lungworms can infect a wide range of wild and domesticated animals. Some of the animal groups most commonly and severely affected include:
Cattle
Lungworms like Dictyocaulus viviparus can cause parasitic bronchitis in calves and cows. Heavy infections lead to pneumonia and calf mortality.
Sheep and goats
Protostrongylid lungworms like Muellerius capillaris cause respiratory disease and reduced productivity in sheep and goats globally. Infections are common in pastured livestock.
Deer
White-tailed deer across North America are susceptible to Parelaphostrongylus tenuis infections. The worms can cause pneumonia, poor coordination, and mortality in deer.
Dogs
Lungworms like Oslerus osleri, Filaroides hirthi, and Angiostrongylus vasorum infect wild and domesticated dogs. They can cause coughing, difficulty breathing, and heart disease.
Cats
The lungworms Aelurostrongylus abstrusus and Capillaria aerophila commonly infect stray and outdoor cats worldwide. They can cause bronchitis, pneumonia, and rapid breathing.
Horses
The equine lungworm Dictyocaulus arnfieldi causes coughing and poor performance in horses. Donkeys and mules are also susceptible to lungworm disease.
Foxes
Foxes infected with Angiostrongylus vasorum lungworms can develop severe cardiac and respiratory disease. The worms have spread rapidly in red fox populations.
What factors promote lungworm transmission to animals?
Some factors that facilitate lungworm infections in animal populations include:
- Grazing on pasture or forage contaminated with larvae.
- Drinking from contaminated standing water sources.
- Eating infected intermediate hosts like snails/slugs.
- Coming into contact with infected feces or respiratory secretions.
- Eating rodents or wildlife reservoirs that are shedding larvae.
- Migration or transportation of infected animals.
- Dense populations of animals on farms or feedlots.
- Warm, moist environmental conditions.
- Lack of routine anthelmintic deworming.
Stray cats and dogs are also more prone to lungworms when they hunt and scavenge infected prey outdoors. Wildlife like deer and foxes can spread lungworms across their habitats and to livestock in shared grazing areas.
Which geographic regions have the most lungworm cases in animals?
Some global hotspots for lungworm infections in animals include:
Europe
Common lungworms affecting livestock and pets in Europe include Dictyocaulus viviparus, Muellerius capillaris, Aelurostrongylus abstrusus and Angiostrongylus vasorum. Heavily grazed pastures and abundant slugs/snails promote transmission.
Southeast Asia
Paragonimus westermani causes lung fluke infections in livestock, dogs, and cats in countries like Thailand, Vietnam, and the Philippines. Infections are linked to eating raw crabs and crayfish.
Central America
Angiostrongylus costaricensis lungworms are widespread in rodents in countries like Costa Rica and Honduras. They can spread to livestock and cause abdominal angiostrongyliasis.
East Africa
Protostrongylid worms are highly prevalent in small ruminants like sheep and goats in Kenya, Ethiopia, and other countries in East Africa, causing major economic losses.
Australia and New Zealand
Angiostrongylus cantonensis has emerged in mollusks in Australia in recent years, causing rat lungworm disease in domestic dogs and wildlife.
Western North America
Parelaphostrongylus tenuis meningeal worms are widespread in white-tailed deer and snail/slug species west of the Continental Divide in North America.
Conclusion
Lungworm infections are endemic in tropical, subtropical, and temperate regions worldwide. They are most prevalent in developing countries where sanitation is poor, and in regions with warm, moist climates that support larval development. Animals that graze outdoors like cattle, sheep, and deer are commonly infected. Stray dogs and cats are also vulnerable due to their hunting and scavenging behaviors.
Public education, improved sanitation, deworming of pets and livestock, and thorough cooking of meat and produce can help control lungworm transmission. Further research is needed to develop more effective anthelmintics and vaccines targeting lungworm infections in humans and animals.
