Heartworm in Pets: How Mosquitoes Spread It

Heartworm is a life-threatening disease, and Dirofilaria immitis, a parasitic worm, is the major cause of this disease. This worm lives in the heart, blood vessels, and lungs of the infected pets, resulting in heart failure, organ damage, and severe lung disease. It is transmitted through the infected mosquito, acting as a vector, which transfers the microfilariae (baby parasitic worms) to a healthy organism.  The larvae require six months to develop into an adult heartworm. 

Which Mosquito Species Spread Heartworm to Pets?

Here are the four mosquito species that spread heartworm to pets:

1. Culex Mosquitoes: They are considered the most active mosquitoes that work from dusk to dawn in metropolitan areas and residential areas. Stagnant, polluted water in clogged gutters, artificial containers, and ditches promotes their growth. 
2. Aedes Mosquitoes: These mosquitoes live close to humans in homes and yards and bite all day. The peak time of Aedes is dawn and dusk, and they are also known as daytime feeders. Flowerpots and useless tires are their breeding places.
3. Anopheles Mosquitoes: Wetlands, freshwater habitats, plenty of vegetation, and slow-moving ponds or streams are the resting areas of Anopheles mosquitoes. They are also known as nighttime feeders or nocturnal. 
4. Psorophora Mosquitoes: These mosquitoes are included in regional or emerging vectors as they appear during heavy rainfall. Psorophora mosquitoes are also known as floodwater species. 

What Are the Symptoms of Heartworm in Pets?

Here are the three symptoms of heartworm in pets:

1. Early or Mild Symptoms: Few to no signs appear at the early or mild stages. The pet faces a persistent dry cough that intensifies with faster exercise. Loss of interest in food results in weight loss in heartworm-infected pets. 
2. Advanced Symptoms: Difficulty in breathing, accumulation of fluid resulting in a pot-bellied appearance, caval syndrome(restriction in blood flow due to dark urine and pale gums), and intermittent vomiting are the symptoms of heartworm in pets. 
3. Symptom Onset: The larvae take months to develop into an adult, due to which the disease is not detected at the time, while it continues to propagate in the body. An annual heartworm checkup is compulsory to diagnose the disease on time. 

Where Do Heartworm-Transmitting Mosquitoes Breed?

The heartworm-transmitting mosquitoes can breed in the following four areas, depending on species type:

1. Culex Species: Dirty or nutrient-rich, stagnant water in ditches, drains, cesspools, sewers, and contaminated puddles are the breeding spaces for Culex species. 
2. Aedes Species: Bird baths, artificial containers, flowerpots, useless tires, and trash are the Aedes species habitats. These mosquitoes can also breed in water-filled cavities of trees (i.e, Western Treehole Mosquito).
3. Anopheles Species: A natural and permanent water source is the first priority for Anopheles species breeding. Their habitat includes freshwater, slow moving ponds, marshes, or wetlands. 
4. Psorophora Species: These species appear in extreme conditions for a temporary period. Foodplains, stand-in pools, or irrigated fields that fill up after heavy rainfall are the habitats of Psorphora species. 

When Are Heartworm-Transmitting Mosquitoes Most Active?

Heartworm-transmitting mosquitoes are of different types that remain active in different time periods. For example, the Culex species remains active between dusk and dawn. Their peak activity period is 11:00 PM to 03:00 AM. Regional or temporary species appear in extreme weather events. Asian Tiger Mosquito(Aedes species) does not rely on darkness to feed. They act in day and are also known as daytime feeders. 

Which Pets Are Most at Risk?

The heartworm disease was reported in all 50 U.S. states in 2026 in pets, including dogs, cats, and ferrets. Dogs are the natural hosts of heartworms, as they can live for 5-7 years and can reproduce in dogs’ bodies. Ferrets are likely to be infected badly due to their small heart size. Even a single worm can affect their respiratory system, leading to sudden death. Cats are indoor pets, yet they can be the host, and the immature heartworms can damage their lungs. This disease is known as Heartworm Associated Respiratory Disease(HARD).

How Can Pet Owners Prevent Heartworms?

Pet owners can follow the following five steps to prevent heartworms:

1. Administer Preventive Medication: FDA-approved tablets are used monthly for dogs and cats to prevent heartworm maturation. Flavored tablets like Heartgard Plus cover intestinal parasites. Spot-on treatments are applied monthly to the cat’s skin. Injections work longer than tablets. For example, ProHeart12(a single veterinary injection) is effective for dogs for a year. 
2. Eliminate Mosquito Breeding Sites: Clean the gutters, remove the useless tires, clear the standing water in bird baths, flowerpots, and rainwater every week to reduce the mosquito infection pressure. 
3. Use Mosquito Repellents (Pet-Safe): Reduce outdoor activities during the mosquitoes’ peak activity periods. Do not use DEET on pets, as it is highly dangerous for them. Prefer using approved repellents. 
4. Install Screens and Barriers: Cover the outdoor areas, like porches and kennels, with a net or screen to limit the mosquito access to the pet. 
5. Regular Vet Checkups: An annual checkup is compulsory to confirm that the medication is working, as the animal can vomit the tablets or rub off the topical medications. 

If you’re seeing mosquitos, schedule a same-day inspection now!

When Should You Call a Veterinarian?

Heartworm disease is irreversible, thus its on-time catch is mandatory. Call the veterinarian if the pet shows a persistent cough, especially during exercise or at night. In case the pet stops playing, tires shortly, and stops during a walk, it shows the heartworm is developing. Sudden onset of vomiting or difficulty in breathing is included in the symptoms.