Answer:
a. viral
Step-by-step explanation:
Virus infections are among the leading causes of morbidity and mortality worldwide. The most dangerous of these infections is that there is no drug treatment for this type of infection. However, there are other forms of treatment.
These infectious agents, viruses, are acellular and outside cells are lifeless. Viruses are formed by DNA and / or RNA and a protein structure that surrounds them called a capsid. Viruses are mandatory intracellular parasites, that is, they are required to enter cells and use their metabolism to replicate, some may even integrate fragments of their DNA into their host's DNA, allowing clinical symptoms to reappear without their host being exposed back to the virus. Some examples of viruses that cause infections in humans are; Adenovirus, Papillomavirus, Herpesvirus, Influenzavirus, Rabdovirus and Togavirus.