A parasite is an organism who lives in or with another organism. Dogs are prone to a host of parasites, and because these nasties depend on your pup for their existence, they can make it difficult for him to gain weight. In fact, many of them cause weight loss.
Roundworm is a common parasitic worms often found in puppies because it's easy to contract and spread and difficult to control. A mother can pass the parasite to her pups while they're still waiting to be born or through her milk to her nursing pups. If your dog plays in an area that contains infected poo, or eats an animal infected with roundworm, he's also at risk. Besides weight loss, other symptoms of roundworm infection include a potbellied appearance, diarrhea, vomiting and a dull coat. Veterinary treatment is necessary, and includes medication to rid your pooch of the worm, as well as preventives to keep it from returning. Roundworm is one of the parasites you can pick up as well, so ensuring your dog is free of this nasty worm is wise, particularly if you have kids who share outdoor space with your dog.
Giardia isn't a worm, but a single-celled parasite taking up residence in your dog's intestine. It's easy to catch -- as simple as drinking water containing the parasite. This tiny parasite causes weight loss, diarrhea, dehydration, loss of appetite, listlessness and soft stool. Diagnosing giardia can be tricky because the cysts aren't passed in stool regularly, giving rise to false negative test results, so the vet usually will request multiple samples to confirm a diagnosis. If a human picks up giardia, it's most often from human-to-human contact.
One of the symptoms of hookworm infection is failure to grow properly. These little parasites use their hook-like "mouths" to attach to a dog's intestinal wall. They feed on large amounts of blood from the intestinal wall's tiny blood vessels, causing anemia, weakness, diarrhea and weight loss. Your pup can catch hookworm by ingesting the parasite through routine grooming, through his skin, or from his mother through her milk or placenta. Because of the potential loss of blood, hookworm infection can have serious consequences for dogs, particularly young puppies who may not survive the blood loss. Your vet can put your dog on a treatment and prevention program to ensure his safety. Hookworm larvae can burrow into human skin, causing itching, but the worms won't mature into adults. It's rare for canine hookworms to penetrate deep enough into human tissue to mature in human intestines.
It's easy for your pup to pick up the whipworm, a common parasite ingested when a dog grooms himself. It's not unusual for an infected dog to not show any symptoms of whipworm infection. When symptoms are shown, they include weight loss, diarrhea and flatulence. Untreated, whipworm can make a dog quite sick, or even cause death. It's fairly easy for a dog to pick up this critter, as it's passed in dog feces.
Since so many parasites are passed through dog feces, good hygiene is a must to prevent infection. If you have a yard, clean it at least weekly to remove your pup's poo and minimize the chance your pooch -- or kids -- will be exposed to microscopic parasites. Annual vet visits should include a fecal sample to check for parasites and treatment, if necessary. If it's not time for your dog's annual vet check and you suspect he's hosting an unwelcome visitor, contact the vet for worming medication; prescription wormers tend to be more effective than over the counter options, and if your pup's on any other medication, it needs to be considered for his treatment.