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Pathogen Pathogenicity:
– Pathogenicity involves infectivity and virulence.
– Koch’s postulates establish causal relationships between pathogens and diseases.
– Meningitis can be caused by various pathogens, while cholera is caused by specific strains of Vibrio cholerae.
– Some pathogens only affect immunodeficient hosts.
– Opportunistic infections often occur in patients with existing conditions.

Types of Pathogens:
– Algae are generally non-pathogenic single-celled eukaryotes.
– Prototheca algae can cause protothecosis in humans and animals.
– Bacteria range in size, and some are pathogenic causing infectious diseases.
– Tuberculosis, caused by Mycobacterium tuberculosis, has a high disease burden.
– Bacterial pneumonia is primarily caused by Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, and Haemophilus influenzae.
– Fungi are eukaryotic organisms that can function as pathogens.
– Approximately 300 fungi are known to be pathogenic to humans.
– Candida albicans is a common cause of thrush.
– Cryptococcus neoformans can cause severe meningitis.
– Prions are misfolded proteins that transmit their folding pattern and cause transmissible spongiform encephalopathy diseases.
– Viroids are small single-stranded circular RNA pathogens that cause plant diseases.

Pathogen Hosts:
– Bacteria serve as hosts to bacteriophage viruses, injecting their genome into bacterial cells for replication.
– Streptococcus pyogenes uses a Cas9 nuclease to cleave foreign DNA, avoiding bacteriophage infection.
– Plants host various pathogens like viruses, bacteria, fungi, and nematodes.
– Notable plant viruses include papaya ringspot virus and tobacco mosaic virus.
– Bacterial plant pathogens like Pseudomonas syringae cause leaf browning in plants.
– Animals can get infected with prions, viruses, bacteria, and fungi, posing risks to both wild and livestock animals.
– Transmissible spongiform encephalopathy (TSEs) in animals include mad cow disease and chronic wasting disease.
– Livestock animals face significant pathogen-related mortality rates in rural settings.

Human Pathogens:
– Humans can be infected with prions, viruses, bacteria, and fungi, leading to symptoms like coughing, fever, and organ failure.
– Immune responses to pathogens can cause symptoms like high fever as a defense mechanism.
– Pathogens can cause severe diseases in humans, impacting global health systems.
– Human pathogens like HIV/AIDS require specific treatments to prevent disease progression.
– Understanding human pathogens is crucial for developing effective treatments and vaccines.

Treatment and Interactions:
– Prion diseases currently have no known effective therapy to halt their progression.
– Vaccines are effective preventive measures against various viral pathogens like influenza and measles.
– Antibiotics like amoxicillin and doxycycline are used to treat bacterial infections, but antibiotic resistance is a growing concern.
– Fungal infections are treated with antifungal medications like clotrimazole for skin infections.
– Pathogenic bacteria, eukaryotic pathogens, and viruses undergo sexual interactions for genetic diversity and repair of genetic damage caused by stressors and immune systems.

Pathogen (Wikipedia)

In biology, a pathogen (Greek: πάθος, pathos "suffering", "passion" and -γενής, -genēs "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

The term pathogen came into use in the 1880s. Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus. Small animals, such as helminths and insects, can also cause or transmit disease. However, these animals are usually referred to as parasites rather than pathogens. The scientific study of microscopic organisms, including microscopic pathogenic organisms, is called microbiology, while parasitology refers to the scientific study of parasites and the organisms that host them.

There are several pathways through which pathogens can invade a host. The principal pathways have different episodic time frames, but soil has the longest or most persistent potential for harboring a pathogen.

Diseases in humans that are caused by infectious agents are known as pathogenic diseases. Not all diseases are caused by pathogens, such as black lung from exposure to the pollutant coal dust, genetic disorders like sickle cell disease, and autoimmune diseases like lupus.

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