Warm weather in Canada brings about a slew of activities unique to the season; going to the beach, camping, fishing, etc. Unfortunately, the same is true for the pests that also come with warmer temperatures. Among them, the mosquito is universally detested for their itchy bites, irritating buzzing, and the risk of transmitting disease. While vector borne diseases involving humans receive plenty of awareness and education, those affecting pets are often overlooked despite sharing similar outdoor spaces as their owners. With proper knowledge and prevention, both you and your pets can enjoy the outdoors without fear of mosquitoes.
Mosquitoes and humans
West Nile virus is a mosquito-borne illness that can cause a range of effects in humans, from no symptoms to a severe, life-threatening neurological disease. The virus, which is primarily spread to people through the bite of an infected mosquito, is most often asymptomatic. However, about 1 in 5 people who are infected will develop West Nile fever, which presents with mild, flu-like symptoms such as fever, headache, body aches, and sometimes a skin rash. In a small number of cases (less than 1%), the virus can affect the central nervous system, leading to more severe conditions like encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord). Symptoms of severe illness include high fever, severe headache, stiff neck, disorientation, muscle weakness, and paralysis. While most people recover completely, those with severe illness, particularly older adults and people with weakened immune systems, may experience long-lasting or permanent neurological effects.
Currently, there is no specific medication or vaccine to cure or prevent West Nile virus in humans. Instead, treatment focuses on managing symptoms. In mild cases, rest, staying hydrated, and using over-the-counter pain relievers for fevers, headaches, and body aches, will be enough to manage through the illness. For the more severe cases, where the virus has affected the central nervous system, hospitalization is often required.
While other mosquito transmitted diseases (Zika, Eastern Equine Encephalitis, Snowshoe Hare virus, etc.) are rare in Canada, climate change may allow these illnesses to be more commonplace in the future.
Mosquitoes and pets
Heartworm
While cats and dogs have a layer of fur to protect them from mosquito bites, it does not make them immune to them or the diseases that they carry. The most common and detrimental condition mosquitos can transmit to pets is heartworms.
Heartworm disease is a serious and potentially fatal condition in pets, and its transmission is entirely dependent on mosquitoes. The process begins when a mosquito bites an animal, such as a dog or coyote, that is already infected with heartworms. During this blood meal, the mosquito ingests microscopic baby worms, called microfilariae, that are circulating in the infected animal’s bloodstream. Over the next 10 to 14 days, the microfilariae mature inside the mosquito into an “infective stage” larvae. When this now-infected mosquito bites a new host, like a dog or cat, the infective larvae are deposited onto the surface of the animal’s skin and enter its body through the bite wound. Once inside the new pet, it takes several months for the larvae to mature into adult heartworms that live in the heart, lungs, and associated blood vessels.
The symptoms of heartworm disease can vary significantly between dogs and cats, and often don’t appear until the infection has progressed. In dogs, early signs can be subtle or non-existent, but as the disease advances, you may notice a persistent mild cough, lethargy, and a reluctance to exercise. More severe cases can lead to difficulty breathing, a swollen belly due to fluid accumulation, and even heart failure. Cats, on the other hand, are an “atypical host,” and their symptoms are often more dramatic and unpredictable. The disease in cats is primarily a lung disease, leading to a condition known as Heartworm Associated Respiratory Disease (HARD), which can mimic asthma with coughing, wheezing, and difficulty breathing. Other signs in cats can include vomiting, loss of appetite, and sudden collapse or even death, which can be the first and only symptom.
Treatment for heartworms is very different for dogs and cats. For dogs, the only FDA-approved treatment is an injectable medication that kills the adult worms. This is a very serious and expensive process that requires multiple visits to the vet and strict exercise restriction to prevent complications from the dying worms. For cats, there is no approved medication to kill the adult worms, as the drug used for dogs is toxic to them. Instead, treatment in cats focuses on managing the symptoms with medication, such as steroids to reduce inflammation, and hoping the cat’s body can clear the infection on its own over time. Due to the high risk and difficulty of treatment, prevention is the safest and most effective way to protect both dogs and cats from heartworm disease.
West Nile Virus
When it comes to West Nile virus, dogs are thankfully not as susceptible to severe illness as humans and horses. Most dogs who are infected will show no symptoms at all. However, in the rare cases where symptoms do appear, they are typically mild and non-specific, often resembling a minor viral infection. These signs can include a fever, weakness, lethargy, muscle spasms, and a loss of appetite. In extremely rare instances, a dog may develop more serious neurological symptoms like a lack of coordination, head tilt, or even seizures. Due to the rarity of symptomatic cases, and the lack of a specific treatment, supportive care, such as keeping your dog hydrated and comfortable, is the main focus. West Nile has not been shown to significantly affect cats.
Mosquito Prevention
Like many hazards, the first step of mosquito protection is prevention. This can be done by eliminating situations where you encounter them. Mosquitoes require stagnant water to reproduce, with a cup of water being enough to support an entire spawn of eggs. Spaces in your backyard may be unintentionally holding water where mosquitoes can grow. Wheelbarrows, clogged gutters, upright buckets, bird baths, and children’s toys can easily hold and store rain water. Also, untreated pools can become habitats for mosquitoes after a few days of sitting outside. Draining these risk areas, or storing them over turned, prevents your backyard from becoming a hot bed for mosquitoes. Larger ponds of woodland pools on your property can be treated with a Mosquito Dunk, a commercial bacterial pesticide that only targets mosquito larvae without harming other aquatic life.
For humans, insect repellent containing DEET (N,N-diethyl-meta-toluamide) is a powerful tool to avoid mosquitoes, as DEET affects their CO2 receptors and keeps them from seeing humans as a food source. This kind of repellent is harmful for pets, and should only be used on people.
For dogs and cats, the most effective preventative measure is a veterinarian-prescribed medication. These medications work by killing the heartworm larvae transmitted by a mosquito bite, preventing them from maturing into adult worms. Available in a variety of forms, including chewable tablets, topical solutions, and even long-lasting injectables, these preventatives are a crucial line of defense. It’s essential to give these medications year-round, as mosquitoes can be active in many regions even during colder months. Talk to your vet to determine the best medication for your pet, as well as the need for annual heartworm testing, which is recommended to ensure the prevention plan is working.
