Diarrhea, bloody stools, weight loss, and anemia can all be signs of illness in your pet, but they may not be visible until your pet is seriously ill. Most parasites only produce eggs, so you can't rely on seeing worms to know that your pet is infected. The only way to make a diagnosis is to have a fecal test for larvae. Heartworms are a dangerous parasite that can cause serious damage to your pet's internal organs and even lead to heart failure.
They are spread through the bite of a mosquito, and some signs that your pet may be infected include a mild but persistent cough, fatigue, and weight loss. Treatment for heartworms can be expensive and difficult for your dog, and unfortunately there is currently no treatment available for cats. The best way to protect your pet from heartworm disease is to prevent it in the first place. That's why it's important to take your pet to the vet for a preventive medication against heartworm disease.
Hookworms are microscopic and therefore hard to detect, but signs that your dog has them include pale gums, anemia, bloody stools, diarrhea, and weight loss. You may also notice that your dog's paws itch and that growth may be delayed. In general, coughing, diarrhea, vomiting and lethargy are all signs that your dog has worms. Other symptoms depend on the type of worm - for example, if your dog has a tapeworm you may notice rapid weight loss or what looks like grains of rice in the stool.
Your vet will take a stool sample to detect the presence of microscopic eggs laid by adult worms. The sample will then be mixed with a solution that makes the eggs more visible under the microscope.