Viroids are acellular, infectious agents consisting only of small, naked single-stranded RNA (ssRNA) molecules, which cause diseases in plants.

Viroids

Virusoids are pathogenic, subviral particles composed of single-stranded RNA (ssRNA) that infect commercially important agricultural crops. Unlike viroids, virusoids are non-self-replicating and require the host cell to be co-infected with a specific helper virus to undergo replication.

Virusoids

Satellite RNAs are pathogenic, single-stranded RNA molecules found in animals that require coinfection with a helper virus to replicate. Unlike plant-infecting virusoids, some animal satellite RNAs are capable of encoding their own proteins.

Satellite RNAs

Nonliving disease agents are acellular pathogens, such as viroids, virusoids, and prions, that are entirely distinct from viruses. These agents consist solely of RNA or proteins, yet they share the viral ability to self-propagate by utilizing host cell machinery to cause disease.

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- Opportunistic pathogen
- Primary pathogen

Types of Pathogens

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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A primary pathogen can cause disease in a host regardless of the host’s microbiota or immune system.

Primary Pathogen

An opportunistic pathogen can only cause disease in situations that compromise the host’s defenses, such as skin, immune system, or normal microbiota.

Opportunistic Pathogens

Nonliving Disease Agents

Prions are acellular, infectious protein particles that do not contain DNA or RNA, cause transmissible spongiform encephalopathies, and are excluded from the tree of life. They are exceptionally small, measuring approximately $${}1/10$$ the size of a typical virus, and are extremely resistant to heat, chemicals, and radiation. Currently, there is no treatment or cure for prion infections.

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