Arthropods are common vectors of disease. A vector is an organism which spreads disease-causing parasites or pathogens from one host to another. Invertebrates spread bacterial, viral and protozoan pathogens by two main mechanisms. Either via their bite, as in the case of malaria spread by mosquitoes, or via their faeces, as in the case of Chagas' Disease spread by Triatoma bugs or epidemic typhus spread by human body lice.