Bacterial infections, such as strep throat or E coli; worm infestations, such as hookworms or tapeworms; protist infections, such as amoebic dysentery, viruses such as cause the flu or AIDS.
Parasites take, but give no benefit back to their hosts. E.G. ticks, head-lice, crabs, scabies, tapeworms, thread-worms..(and MANY more)... in humans. Ticks are a great example! There are cattle...
Related ads:
Shopping for Science deals?
Find Coupons and Promo Codes on Coupons by Answers.com