What must a pathogen that is outside the host accomplish in order to infect the host...

What must a pathogen that is outside the host accomplish in order to infect the host successfully and have its descendants infect another host?

Expert Solution

The ability of a pathogens to produce disease in a host is termed pathogenicity. And the degree of pathogenesis is termed virulence.

Pathogenesis depends on several factors

1)Infective dose : which again is related to virulence of pathogen(small infective dose is sufficient if organism is highly virulent), host immunity, ability of the organism to resist barriers such as gastric acidity.

2)First step in pathogenesis is adhesion of pathogen to host cell receptors using adhesins, which includes fimbria, lipoteichoic acid, cell surface lectin. Biofilm formation in bacteria helps in strong adherence to structures such as catheter, valves etc.

3)Next step is invasion which helps in spread of pathogen in host tissues. This is helped by virulence factors such as virulence marker antigen, enzymes which include hyaluronidase, collagenase etc

4)Next is intracellular survival of pathogen which is helped by antiphagocytic factors such as capsule, cell wall proteins such as protein A of Staphylococcus aureus, M protein of Streptococcus, and cytotoxins .Survival of pathogen is followed by multiplication in host tissues.

5)Other virulence factors includes toxins

Toxins can be either exotoxin or endotoxin. These cause various biological effects in host.

6) Another virulence factor is secretory system in bacteria. This help in translocation of proteins, enzymes and toxin from the cytoplasm of bacteria to exterior.

Various virulence factors are encoded by genes located in pathogenicity islands in bacteria (these are large genomic islands)

All these factors help the pathogen in establishing a disease in the host. For transmission to another host, there should be a susceptible host, a portal of exit for pathogen from the infected host and appropriate modes of transmission (airborne, droplet, contact, ingestion or inoculation). In some pathogens, vectors are also needed for transmission.

gladiator answered 1 year ago

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