Both you and your pup are potential hosts to the giardia and trichinosis parasites. The parasites are very different, and each affects its host in different ways. One thing both parasites have in common is Sammy can contract either parasite without displaying symptoms of infection.
Giardia is a single-celled parasite that causes an intestinal infection in your pup. It takes one of two forms: the type feeding in the gut of an infected animal and a hardy cyst shed in poop, able to survive for months -- especially in wet environments. If Sammy swallows a giardia cyst, it passes into his intestines where it transforms into its feeding form, known as a trophozoite. It attaches to his intestinal wall to feed. Trophozoites divide to reproduce; some transform into cysts, and eventually are passed in Sammy's poo. Your pooch can pick up giardia by drinking contaminated water or sniffing or eating the cysts from contaminated ground. Often dogs don't show signs of giardia infection, however, when they do, symptoms include foul-smelling diarrhea, soft or watery stool, often with a green tinge, excess mucus in stool, and occasionally, blood in the stool. Once in a while a dog may vomit or be lethargic.
It's fairly easy for a dog to pick up giardia, particularly in environments where there are a large number of dogs, such as kennels and animal shelters. If you suspect Sammy may have picked up this tiny yet potent parasite, the vet will perform a fecal smear to confirm its presence. The antibiotic metronidazole is often the treatment of choice, sometimes paired with the antiparasitic medication, fenbendazole. Generally, giardia infection comes with a favorable prognosis, however if a dog is geriatric or has a compromised immune system, he's at risk for complications. If Sammy has giardia, his living space should be disinfected with a solution of one or two cups of bleach per gallon of water. It's possible for you to pick up the parasite from Sammy, so be sure to wash your hands thoroughly after interacting with him.
Trichinosis, or trichinellosis, is another parasite you and Sammy can catch. Unlike giardia, it's a worm known as a nematode. Just about every mammal is susceptible to infection, which happens when meat containing Trichinella larvae is ingested; pork is the most common meat affected. When the larvae are ingested, they migrate throughout the body, forming cysts in muscles. The larvae live in the cysts for years and if they're ingested by another host, they'll continue to develop. If they pass through the intestine before they're mature, they can infect other animals. It's hard to know if Sammy has trichinosis, because dogs often don't show symptoms. When they do, they include muscle inflammation, pain and stiffness, diarrhea and vomiting. If he has a history of eating raw meat or rodents, he's at risk for trichinosis.
If the vet suspects Sammy has trichinosis, he'll focus on your pup's diet when reviewing his medical history. Lab tests, including a complete blood count, can provide clues; high numbers of the white blood cells known as eosinophils can indicate a parasitic infection. A fecal sample is helpful and sometimes, muscle samples show the parasite. The only medication generally prescribed is an antiparasitic drug to reduce the number of parasites in the muscles. The best way to steer clear of trichinosis is to avoid undercooked pork products.