( ( ( Internal and ) ( External Parasites ) ) ( ( can ( affect ( both ( ( animals and ) humans ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Internal)) (CC and) (NP (NNP External) (NNP Parasites))) (VP (MD can) (VP (VB affect) (NP (CC both) (NNS animals) (CC and) (NNS humans)))) (. .)))
Internal and External Parasites can affect both animals and humans.
(ROOT (S (NP (NNS Nematodes)) (VP (MD can) (VP (VB be) (NP (NP (DT a) (NN parasite)) (PP (IN of) (NP (DT both)))))) (. .)))
Nematodes can be a parasite of both.