to live in or overrun to an unwanted degree or in a troublesome manner, esp. as predatory animals or vermin do

Sharks infested the coastline.

to be numerous in, as anything undesirable or troublesome

the cares that infest the day.

Archaic . to harass.

adjective

abound , annoy , assail , beset , crawl , crowd , defile , fill , flock , harass , harry , infect , invade , overspread , overwhelm , pack , penetrate , pester , plague , pollute , press , ravage , swarm , teem , throng , worry