Bullfrogs are known to have many viruses and bacteria. However, only a few of them are important to nature. Bullfrogs were blamed for an intraerythrocytic virus outbreak in Canada in 1997. They were also blamed for a chytrid fungus that spread into Arizona in 2000. The chytrid fungus is believed to be one of the major causes of the decline in amphibian populations. Many bullfrogs can have parasites including helminths, trematodes, nematodes, protozoans and leeches.