The term "serious infestation" means there is a large and troubling presence of unwanted organisms or pests in a particular area. It suggests that the situation is significant and requires attention to resolve. Full definition
In the cases of serious infestation, a flea or tick's propensity to suck blood could lead to your dog suffering from anemia. (herepup.com)
At low concentrations, this odor is said to be similar to the scent of coriander, but in serious infestations, the odor is deeply unpleasant. (thefashionablehousewife.com)
You'll want to opt for medical grade treatments for serious infestations. (shepped.com)