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Transmission
Establishing and maintaining the B. pertussis pathogen population is difficult considering it only naturally infects humans and there are no animal reservoirs to extend transmission in its environment. In order for the infection to be spread to a host, the transmission chain must be uninterrupted and B. pertussis must be in the appropriate conditions for survival.

Transmission involves ________

Transmission rates are expected to rise as the host experiences their most contagious stage when the total viable count of B. pertussis is at its highest. After the host coughs the bacteria in their respiratory airways will be exposed into the air by way of aerosolized droplets, threatening nearby humans.

B. pertussis is considered an extracellular pathogen, but the evolution of human population density and gene modification has contributed to its ability to survive within respiratory epithelial and phagocytic cells.

(add something about Bvg regulating the change in  phenotype to allow for B. pertussis to survive in the air while being transmitted…)

The evolution of B. pertussis has also created a much more contagious pathogen by changing genes controlled by the BvgAS system.

Bvg is responsible for regulating the genes expressed by B. pertussis and can influence metabolic processes within the pathogen.

https://www.tandfonline.com/doi/full/10.1080/21505594.2021.1980987

Pertussis was first speculated to be transmitted by airborne particles in 1916.

Transmission #2
Transmission involves the spread of respiratory aerosols (CITE) by a host that sneezes or coughs to infect another nearby host.

In order for the infection to be spread to a host, the transmission chain must be uninterrupted and B. pertussis must be in the appropriate conditions for survival.

In order to understand how B. pertussis survives in order to be transmitted, it is important to identify if it lives within or outside of a host’s cells. This leads to the classification of a pathogen as intracellular or extracellular. When determining if a pathogen is considered an intracellular or extracellular microorganism, its transmission mechanism and preferred location of colonization.

The incapacity for B. pertussis to live within amoeba has led to its classification as an extracellular pathogen. Although B. pertussis is considered an extracellular pathogen, the evolution of human population density and gene modification has contributed to its ability to survive within respiratory epithelial and phagocytic cells.

Establishing and maintaining the B. pertussis pathogen population is difficult considering it only naturally infects humans and there are no animal reservoirs to extend transmission in its environment.

Transmission rates are expected to rise as the host experiences their most contagious stage when the total viable count of B. pertussis is at its highest. After the host coughs, the bacteria in their respiratory airways will be exposed into the air by way of aerosolized droplets, threatening nearby humans.

Evolution
It is believed that the genus Bordetella may have evolved from ancestors that could survive in the soil according to 16S rRNA gene sequencing data. 16S rRNA is a component of all bacteria that allows for the comparison of phyla within a sample. In this case, it was determined that although pathogenic bordetellae, like B. Pertussis have adapted to specifically infect humans, they are still able to multiply and thrive in soil conditions.

B. Pertussis has a greater opportunity to spread to its next host when B. pertussis invades epithelial cells of its host.

Studies have also shown that the pathogen  is able to survive inside pulmonary alveolar macrophages

This means that evolution has allowed for the intracellular survival strategy of B. pertussis to _____________-

Warfel JM, Beren J, Merkel TJ. Airborne transmission of Bordetella pertussis. J Infect Dis. 2012 Sep 15;206(6):902-6. doi: 10.1093/infdis/jis443. Epub 2012 Jul 17. PMID: 22807521; PMCID: PMC3501154.

Yanina Lamberti, Juan Gorgojo, Cintia Massillo, Maria E. Rodriguez, Bordetella pertussis entry into respiratory epithelial cells and intracellular survival, Pathogens and Disease, Volume 69, Issue 3, December 2013, Pages 194–204, https://doi.org/10.1111/2049-632X.12072

Trainor EA, Nicholson TL, Merkel TJ. Bordetella pertussis transmission. Pathog Dis. 2015 Nov;73(8):ftv068. doi: 10.1093/femspd/ftv068. Epub 2015 Sep 14. PMID: 26374235; PMCID: PMC4626651.

https://academic.oup.com/femspd/article/73/8/ftv068/2467637?login=false

Belcher T, Dubois V, Rivera-Millot A, Locht C, Jacob-Dubuisson F. Pathogenicity and virulence of Bordetella pertussis and its adaptation to its strictly human host. Virulence. 2021 Dec;12(1):2608-2632. doi: 10.1080/21505594.2021.1980987. PMID: 34590541; PMCID: PMC8489951.

Vaccine-driven evolution
continues to reemerge in countries that have high vaccine coverage

The emergence of PRN-deficient B. pertussis strains suggest that the bacteria is evolving.

PRN is located on the surface of many Gram-negative bacteria, like B. pertussis, and acts as an autotransporter protein to attach to its surroundings.

Ma L, Caulfield A, Dewan KK, Harvill ET. Pertactin-Deficient Bordetella pertussis, Vaccine-Driven Evolution, and Reemergence of Pertussis. Emerg Infect Dis. 2021 Jun;27(6):1561-1566. doi: 10.3201/eid2706.203850. PMID: 34014152; PMCID: PMC8153889.

Belcher T, Preston A. Bordetella pertussis evolution in the (functional) genomics era. Pathog Dis. 2015 Nov;73(8):ftv064. doi: 10.1093/femspd/ftv064. Epub 2015 Aug 21. PMID: 26297914; PMCID: PMC4626590.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4626590/