There are 4 important zoonosis or diseases transmittable from dogs to humans.
1. Toxocara Canis
The common round worm of the dog attracts the most publicity as a potential threat to human health from dog faeces.
Each adult female worm can lay 84, 700 eggs per day. Each gram of faeces can contain 15,000 eggs. The eggs develop after being passed by a dog into an infective stage and can survive on pasture (including rugby pitches!) for months if not years. Dogs don’t need to actually defecate on the pitch to pass the eggs on as they can be attached to the skin, feet and perianal area.
If ingested by a human the worm larvae can migrate through the body. This is called visceral larva migrans.
· Migration to the liver can cause hepatomegaly (enlargement of the liver) or eosinophilia (change in white blood cells).
· Migration through the lungs has been associated with wheezing asthma like symptoms.
· Migration through the brain has been associated with epilepsy (though this remains unproven).
· Migration to the eye can cause partial loss of vision or blindness. More commonly a retino blastoma grows at the back of the eye – this can be removed but this requires laser treatment. Rarely the optic nerve is affected causing blindness.
There are 50 – 60 cases a year of visceral larva migrans reported in the UK and it is thought many more go undetacted and/or unreported.
2. Leptospirosis.
Leptospira are a bacterium that can be passed in dogs urine and remain viable in damp conditions. They enter humans through abraded skin (grazed knees, etc…) or through the mouth. They cause Weils Disease which involves hepatitis and jaundice. A severe condition in human beings.
3. Cryptosporidia
An important enteric pathogen commonly carried by dogs and transmissible to humans. This can cause severe diarrohea which can occasinally last for several months.
4. Salmonella
Rare in dogs but can cause enteritis (inflammation of the bowel) if transmitted to humans.