Dogs are hardly a public health hazard. Well perhaps not the dogs themselves but there is a risk to public health and that is
toxocariasis.
Toxocariasis
Toxocariasis is an infection of the round worm Toxocara canis. It is a zoonotic disease that is spread via unwashed vegetables and dog faeces. Young children in particular are at risk due to their weaker immune systems and because they are more likely to expose themselves by ingesting the eggs. A puppy can pass as many as 15,000 eggs per gram of faeces, and they are a major source of environmental contamination.
Each T. canis female can lay up to 700 eggs a day. These are passed out when the dog defecates and can survive for up to three years in soil. After two to three weeks of warm weather the eggs develop into an embryo state, containing larva - this is when they become infective to dogs and people.
The larvae try to migrate through the human body as they would in a dog's, but the human body treats them as foreign material, which causes a reaction and tissue damage.
There are two types of toxocariasis: visceral larva migrans (VLM) and ocular larva migrans (OLM).
In VLM, the larvae reach the liver, causing inflammation and symptoms such as abdominal pain and pyrexia. Most people recover spontaneously.
OLM occurs when a migrating larva reaches the eye. It causes a granuloma to form on the retina, causing significant visual impairment and in severe cases even blindness.
There are about 12 new cases of OLM diagnosed annually in the UK.