Margaux Baum & Jennifer Viegas 
Parasites [PDF ebook] 

Though not thought about as much as viruses or bacteria, parasites are behind much sickness and suffering in both animals and humans all over the world. Parasites range from microscopic protozoans to insects like ticks and lice and intestinal worms. What they all have in common is that their survival comes at the expense of other living things. This book gives readers a solid introduction to these unpleasant but fascinating organisms, describes how they lead to illness, and discusses preventative measures and cures.