It's crucial for dog owners to be aware of common parasites because some of them can be fatal. So how do you keep your dog healthy? "Prevention, prevention, prevention," says Dr. Jim Berry, a veterinarian in Fredericton.

1. Heartworm
What is it: "Heartworm is a disease that's spread by infected mosquito bites," says Dr. Berry.

Symptoms: Six to seven months after your dog is bitten by an infected mosquito, the parasite will reach the heart, where it matures into long, thin worms, explains Dr. Berry. According to the Canadian Veterinarian Medical Society, if your dog has heartworm, it may have a cough or tire quickly when exercising. But often, dogs don't display any symptoms. Unfortunately, heartworm can cause heart or lung problems, which can be fatal.

Prevention: The good news is heartworm is 100-percent preventable through medication. Where you live dictates what kind of preventative treatment, if any, your dog needs, so talk to your vet about your options. "Warm areas like southern Ontario and parts of southern Quebec are the most common areas for [infected mosquitos]," he says.

Also talk to your vet about your dog's lifestyle: Where do you walk your dog? Does your dog travel with you? These factors affect your dog's heartworm risk.

2. Fleas
What is it: If your dog gets fleas, the problem isn't the fleas themselves, but the eggs they lay. "The eggs do not stay on the pet," says Dr. Berry. "They drop off wherever your pet is—outside, in your house, in your bed." Those eggs hatch, then the fleas jump back on your pet and lay more eggs, resulting in an infestation.

Symptoms: Fleas are easy to diagnose because you can often see the fleas or see irritated skin where your dog has scratched at the fleas.

Prevention: It's best to buy your flea-prevention medication from your vet. "They are going to be more expensive," says Dr. Berry. "But they are incredibly safe compared to the products over the counter and they are also far, far more effective."

3. Ticks
What is it: Brush area or long grass is breeding ground for ticks, says Dr. Berry, but it's also a popular place for dogs to run and play. "The ticks get onto your dog and bite." Ticks stay on your dog for days, spitting out bacteria that cause Lyme disease.

Symptoms: "There are a lot of different syndromes caused by Lyme disease," says Dr. Berry. "It can be neurological, heart, kidney." The most common symptoms in dogs are shifting arthritis and kidney problems, which can be fatal.

Prevention: Lyme disease is preventable through medication, but talk to your vet to see if your dog is at risk of getting Lyme disease, suggests Dr. Berry. "I have clients whose pets live in apartment buildings and they're walked on a leash in parks, on grass or pavement," says Dr. Berry. "Do I really worry about them having Lyme disease? No." If you and your dog live in the countryside, you definitely need a tick-prevention medication.

4. Internal parasites
What is it: There are many different intestinal parasites, but the most common is roundworm. "Dogs get roundworm mainly from eating disgusting things in the backyard," says Dr. Berry. "They're not very discriminating about eating other dogs' stool."

Symptoms: Dr. Berry explains that roundworms are subclinical, so they don't cause any symptoms, and you won't see them. The problem is that your dog will defecate microscopic eggs, which not only reinfect your dog but pose a risk to children and immunodeficient people.

Prevention: Like with other common parasites, you should talk to your vet about the best prevention medication for your dog, says Dr. Berry.

Best parasite-prevention tips
Prevention is key to keeping your dog free of common parasites. So we spoke with Melissa Long, a veterinary technician for Pets Plus Us, about preventative care. She offers the following tips to better care for your four-legged friend.

1. Biannual fecal exam: Since you can't see intestinal parasites, a biannual fecal exam will determine if your dog is infected. "We really want to be proactive in screening for those types of things," says Long.

2. Check your dog after you've been outside: "When you've come back from camping or being outside, we really want you to run your hands over their bodies, look for any lumps or bumps," says Long. "Oftentimes, you can see or feel ticks on the skin, so get really familiar with your dog's anatomy."

For more tips on keeping your dog healthy, check out our pet owner's guide.