Dogs can catch stomach flu viruses, but they cannot catch it from humans, and the type of flu they do get is specific to dogs. The stomach flu that dogs can catch is called gastroenteritis.
Gastroenteritis in dogs has a number of causes, most of which are due to infectious pathogens, including bacteria, viruses, fungi and parasites. It can also develop in a dog as a result of tumors, poisoning, thyroid disease, Addison's disease and foreign bodies, including intussusception.
The most prominent symptoms of gastroenteritis are continuous vomiting and diarrhea, but other symptoms include anorexia, weight loss, lethargy, fluid loss, dehydration and hypovolemic shock. Dogs suffering from the stomach flu are usually tender around the abdomen and resist being picked up or handled. They also sometimes develop low-grade fevers.
Fortunately, gastroenteritis is a fairly easy disease to treat. According to VCA Animal Hospitals, treatment involves rehydration and restoration of blood. Depending on the severity of the flu and the amount of fluid lost, the rehydration can be given orally or intravenously. Food and water should be slowly reintroduced to the dog, and recovery usually begins to occur rapidly after treatment.
To best prevent infection or reinfection, petMD recommends food additives including probiotics, prebiotics and synbiotics. These additives help restore and reinforce intestinal microflora and should prevent the dog from catching stomach flu viruses.