Weil’s Disease is caused by micro organisms and the biggest chance of infection is in the spring and autumn. It can be fatal in younger dogs and humans can be infected by dogs and rats. Dogs can be infected by swimming in or drinking contaminated water, through small skin wounds and the mucous membranes. The symptoms are high fever, doziness, muscle pain, lack of appetite, vomiting and very thirsty. There could also be nosebleeds, dark urine and sometimes Yellow Fever. It could be transmitted through the urine of infected dogs and rats.