A parasite is a type of a symbiont.
Parasitism describes a relationship between two organisms where one benefits, and the other is harmed. The parasite is the organism that benefits from the relationship, while the host is harmed by the relationship. Parasites can be a number of things including plants, animals and even viruses and bacteria.
"Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor."
https://www.britannica.com/science/benzaldehyde
https://en.wikipedia.org/wiki/Benzaldehyde
Sounds like infectious would fit.
The answer is, How fast distant galaxies are moving away from us
The main responsible for the delay among the atrial and
ventricular contractions is the action potential conduction velocity of the AV
node cells. If the atria and ventricles contract simultaneously, atria cannot
give any help in filling the ventricles, which is needed, especially in those
with stiff ventricles as in the elderly. Hence atria have to contract first and
then the ventricles.