It's usually not a good idea to eat while you're feeling sick to your stomach and are on the verge of throwing up.
Non-lethal parasites affect deer, caribou, and other ungulates (hoofed animals). Infections that make them sick really help the ecology.
"Parasites are notorious for their deleterious effects on host physiology and behavior, but these effects are seldom explored in the context of the wider ecosystems they inhabit."
Koltz and colleagues used computer modeling and a worldwide meta-analysis to assess plant, caribou, and helminth data.
Lethal parasites may have knock-on effects on the ecosystem, comparable to predators killing their prey. Both may change an ecosystem's dynamics.
In the 19th century, the rinderpest virus killed up to 90% of domestic and wild cattle in sub-Saharan Africa, but a population rise following a successful vaccination effort reduced fire frequency.