The phrase "as a pernicious" is correct and usable in written English.
It can be used to describe something that is harmful or destructive in a subtle or gradual way, often in a negative context.
Example: "The spread of misinformation can act as a pernicious influence on public opinion."
Alternatives: "as a harmful" or "as a detrimental".
Things have changed since Time magazine, in 1966, described homosexuality as a "pernicious sickness".
Yet the government's sentencing memo paints Mr. Rajaratnam as a pernicious figure: "He corrupted old friends.
In the recent play "Bengal Tiger at the Baghdad Zoo" Uday figures in the afterlife as a pernicious ghost.
At various times this exceptional view of self has been used as a pernicious ideology, justifying slaughter and discrimination.
That the mission could be perceived as a pernicious new form of imperialism was totally alien to Bush.
A leaked US diplomatic cable described China in Africa as a "pernicious economic competitor with no morals".
"We demand an end to payment by results as it is a pernicious and discriminatory practice that does nothing to improve teacher morale and the education our children receive," she said.
But while a few people here see the case as evidence of a pernicious spiral started by priestly abuse, most parishioners have forgiven and stood behind Father Audibert who, like Father Doucette, declined to be interviewed.
At the same time, a crackdown on social security fraud — a problem considered as pernicious as the country's widespread tax evasion — has seen some results.
This moral panic, masquerading as vigilant protection, has a pernicious effect upon society.
Amazon says the "groundbreaking biography … vividly details the passions that drove Houdini to perform ever-more-dangerous feats, his secret life as a spy, and a pernicious plot to subvert his legacy".
