Answer:
infectious agent
Explanation:
The basic elements of the transmission chain of parasitic infections are the host, the infectious agent and the environment.
The host in a transmission chain can be either man or an animal, always exposed to the parasite or the transmitting vector. In the parasite-host relationship, it may behave as a carrier with no symptoms or as an individual with symptoms, both of which are capable of transmitting the disease. In the case shown above, the host is Christopher.
The infectious agent is a living being capable of recognizing its host, penetrating, developing, multiplying in this living being, and then going out to reach new hosts. In the case shown in the question above, the indecious agent is chicken pox.
The environment is the space constituted by physical, chemical and biological factors, whose intermediates are influenced by the parasite and the host. In the case of the above question, the environment is the day care center of Cristopher's son.
