Leptospirosis is caused by bacteria (Leptospira spp.) that have a world-wide distribution and can infect any mammal. Dogs contract the disease through contact with infected urine or water. The most common signs reported in dogs are fever, anorexia, vomiting and diarrhea, but signs can vary. Kidney and liver damage have been reported in some dogs. Antibiotic therapy is needed to clear the organism, and supportive care and hospitalization is required in the most severe cases.

Mortality rates are 20 percent, although some experts report mortality rates as high as 70 percent in the most severely affected individuals.

Cyanobacteria range in colour from green–blue, to brown–red and form surface mats of scum or foam. They release cyanotoxins, which, on contact with skin, can cause rashes, hives or blisters. When inhaled, the bacteria can cause cold- or asthma-like symptoms. ­Ingestion causes ­gastroenteritis, as well as liver, kidney and nervous ­system toxicity.

This parasite is found in the faeces of infected humans and cattle. Ingesting it can cause cryptosporidiosis. Symptoms include diarrhoea, abdominal cramps, fatigue, loss of appetite, nausea and vomiting. These can persist for several weeks. The parasite consists of a single cell, known as an oocyst , which is protected by a tough shell. Once oocysts enter the body, they release sporozoites which reach the intestines and lungs.

A common waterborne parasite around the world, Giardia affects 200 million people each year. Symptoms include diarrhoea, dehydration and abdominal pain. The hardy, spore-like cysts  are resistant to UV, iodine and chlorine, and as few as 10 can cause infection. Giardia begins to wreak havoc in your gut 1–3 weeks after digestion. Stomach acids break down the hard shells of the cysts, releasing ‘trophozoites’  into the small intestine. Here, they reproduce and attach to the intestine. Treatment involves antibiotics and hydration therapy.

Pythiosis is caused by a type of fungus (Pythium insidiosum) that causes very serious and often fatal infections of the skin or intestinal tract. Clinical signs include ulcerated, non-healing skin lesions, weight loss, vomiting, diarrhea and bloody stools.Surgery to remove lesions on the skin and in the bowel is the treatment of choice for this disease, but many times the lesions are too extensive to remove.

Protothecosis is caused by an algae (Prototheca spp.) found in warm, humid regions. The organism can cause skin lesions as well as central nervous system signs (such as seizures, blindness and incoordination) and diarrhea, vomiting and weight loss if the large intestine is involved.