It's August and that means that we'll soon be celebrating World Mosquito Day (20th August) to commemorate the discovery in 1897 by Sir Ronald Ross that the female Anopheles mosquito transmits Malaria. This provided the foundation for scientists across the world to better understand the deadly role of mosquitoes in transmitting diseases.
We've written about mosquitoes on this blog before, and I was pretty sure I knew all there was to know about the diseases they carry that affect people. But did you know that in addition to carrying Malaria, Zika and Nile Fever, mosquitoes ALSO carry an illness called Heartworm? I didn't, and it turns out that Heartworm (Dirofilaria immitis) can be extremely dangerous for a variety of mammals, including our beloved dogs and cats.
What is Heartworm?
According to the American Heartworm Society, Heartworm is "caused by foot-long worms (heartworms) that live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body."
Transmitted by Mosquitoes
Adult female heartworms produce microscopic baby worms called microfilariae that circulate in the infected animal's bloodstream. When a mosquito bites that infected animal, they ingest these baby worms.
The microfilariae take 10 - 14 days to mature into heartworm larvae inside the mosquito. When the infected mosquito bites another animal, the larvae are transmitted to the new host. The larvae enter the host's bloodstream and settle in their heart and lungs. Once there, they grow to approximately 30cm long and become sexually mature. This takes 6-7 months, and worms have the appearance of cooked spaghetti!
Adult heartworms can live in the host's heart and lungs for up to 7 years. The cycle continues when infected blood is transmitted via mosquito bites to non-infected animals. The worms are big enough to be seen using ultrasound and x-ray images (spaghetti!) and can also be detected with blood tests.
Symptoms of Heartworm
The disease shows up differently in cats and dogs, as dogs are a natural host for heartworms, and cats are an atypical host (this means that most worms don't survive until the adult stage in cats).
Heartworm in Dogs
As dogs are the heartworm's natural host, worms mature, mate and reproduce in dogs. The number of worms can increase substantially if left untreated - dogs have been known to harbour hundreds of worms in their bodies! This can cause lasting damage to the heart, lungs and arteries, and can affect the dog's health and quality of life.
In the early stages of the disease, dogs may show few or no symptoms, but the longer the infection persists, the more likely it is that symptoms will develop. To begin with, these include:
- a mild cough
- reluctance to exercise
- decreased appetite
- weight loss
As the disease progresses, dogs may develop heart failure and a swollen belly caused by fluid in the abdomen. Dogs with large numbers of heartworms may experience cardiovascular collapse caused by a sudden blockage in the heart. This is called caval syndrome and symptoms include sudden laboured breathing, pale gums, and dark or bloody urine. Without immediate surgery to remove the blockage caused by the worms, few dogs survive.
Heartworm in Cats
Cats are an atypical host for heartworms, which means that the disease presents differently in cats. Most worms don't survive to the adult stage, and cats typically have very few adult worms lodged in their hearts and lungs. Many cats have no adult worms at all, which you'd be forgiven for thinking would be a good thing. What it actually means is simply that the disease often goes undiagnosed.
Whilst cats are unlikely to die from caval syndrome, even immature worms can cause real damage in the form of heartworm associated respiratory disease (HARD) - which is often indistinguishable from mature adult heartworm infection.
It's important to note that the medication used to treat heartworm infections in dogs can't be used for cats. Prevention really is the only means of protecting your cats from the effects of this disease.
How can you protect your pets?
The only way that Heartworms is spread is through the bite of an infected mosquito, so it makes sense to eliminate any potential breeding grounds for mosquitoes on your property. Not only will your pets be grateful, but so will you when it comes to those long summer evenings.
Also, consider bringing your pets indoors in the evenings when mosquitoes are most active. You can talk to your vet about preventative treatments, but we highly recommend eliminating mosquito breeding sites first to break the cycle.
Taking some basic preventative measures at home can help ensure that your pets aren't at risk from this horrible disease. For those of you with a serious mosquito problem that is resisting DIY treatment, I recommend calling in the experts. Rentokil will be able to provide you with a long-lasting, professional solution to your mosquito problem.