Heartworm and intestinal parasites are a common problem for dogs, including Chihuahuas. There are several ways that your dog can pick up these worms. First, they can eat worm eggs or larvae that are found in the grass or soil outside your home. These parasites can survive for a long time and can infect your dog when they accidentally swallow the eggs. Second, if your dog likes to hunt, they can catch worms from other infected animals they come into contact with. It's important to keep an eye on your dog and prevent scavenging. Third, dogs can contract worms while grooming themselves. Roundworm eggs can attach to their coat and can be swallowed during grooming. Fourth, swallowing fleas while grooming can lead to tapeworm infestations. Fleas can carry tapeworm larvae, which can develop into adult tapeworms in your dog's intestine. It's important to keep up with regular flea prevention to reduce the likelihood of a parasite infestation. Fifth, roundworms can be transmitted from an infected mother to her puppies. This can happen during pregnancy via the placenta or during nursing. Young puppies are especially at risk and regular worming treatments are important. Finally, heartworm is passed to dogs through mosquito bites. Heartworm can cause serious health issues and even death in some cases. It's important to protect your dog against heartworm. Overall, it's critical to deworm your dog regularly to protect them from these parasites.