Quick questions on Pathogen adaptations for entry and transmission: HSC Biology Module 7

Surface attachment proteins. Many pathogens carry surface molecules that bind to specific host cell receptors. Influenza haemagglutinin binds to sialic acid on respiratory cells. HIV gp120 binds to CD4 receptors on T helper cells. Plasmodium sporozoites bind to hepatocyte surface proteins.

Antigenic variation. Influenza and HIV mutate rapidly (antigenic drift) so that antibodies raised against earlier strains do not recognise new ones. Trypanosoma brucei changes its surface glycoprotein coat repeatedly, evading antibody recognition.

Inducing symptoms that spread the pathogen. Vibrio cholerae triggers severe watery diarrhoea, flooding water supplies with new bacteria. Influenza triggers coughing and sneezing, aerosolising the virus. Rabies virus alters host behaviour to encourage biting.

Many pathogens carry surface molecules that bind to specific host cell receptors. Influenza haemagglutinin binds to sialic acid on respiratory cells. HIV gp120 binds to CD4 receptors on T helper cells.

Streptococcus pyogenes produces hyaluronidase and streptokinase, which break down connective tissue and clot proteins, allowing the bacterium to spread through skin and soft tissue. Some fungi secrete keratinases to digest skin.

Bacteriophages and many bacterial pathogens use pili and fimbriae to attach to host cells before invasion. Salmonella uses a type III secretion system, a needle-like structure, to inject proteins that force gut cells to engulf the bacterium.

Bacillus anthracis forms endospores that resist heat, drying and chemical insult, allowing the pathogen to remain infectious in soil for decades. Giardia lamblia forms tough cysts that survive in water until ingested.

Influenza and HIV mutate rapidly (antigenic drift) so that antibodies raised against earlier strains do not recognise new ones. Trypanosoma brucei changes its surface glycoprotein coat repeatedly, evading antibody recognition.

Streptococcus pneumoniae has a polysaccharide capsule that prevents phagocytosis. Pseudomonas aeruginosa forms biofilms that block antibiotics and immune cells.

Viruses replicate inside host cells, hidden from antibodies. Mycobacterium tuberculosis survives inside macrophages, the very cells meant to destroy it.

Vibrio cholerae triggers severe watery diarrhoea, flooding water supplies with new bacteria. Influenza triggers coughing and sneezing, aerosolising the virus. Rabies virus alters host behaviour to encourage biting.

Plasmodium has separate stages for the mosquito and human host, with surface proteins matching each. The parasite manipulates mosquito feeding behaviour to favour transmission.

Norovirus is non-enveloped and resists drying, surviving on surfaces for weeks. Prions resist boiling, UV and standard disinfection, allowing transmission via contaminated surgical instruments.

Measles virus produces enormous numbers of virions in the airway, and an infected person typically infects 12 to 18 susceptibles in a fully susceptible population.

Markers want specific structural or biochemical features, not vague behaviours.