A pathogen is an infectious 'germ', such as a virus, bacteria, fungi or parasite, which causes a disease. This ability is called pathogenicity.

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The body has many ways to defend against some of these pathogens in the form of the human immune system and by some "helpful" bacteria present in the human body. However, if the immune system or "good" bacteria is damaged in any way (for example, chemotherapy, HIV, or antibiotics being taken to kill other pathogens), pathogens that were being held back can grow and cause harm to the host. Such cases are opportunistic infections.

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Some pathogens cause widespread infections called pandemics. These include the bacterium Yersinia pestis which has caused the Black Death, and the SARS-CoV-2 virus that has caused the Covid-19 pandemic.

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Séard atá i bpataigin ná 'frídín' tógálach, mar víreas, baictéir, fungais nó seadán, atá ina udár galair. Tugtar pataigineacht ar an gcumas seo.

 

Tá go leor bealaí ag an gcorp cosaint a dhéanamh i gcoinne cuid de na pataiginí coitianta i bhfoirm an chórais imdhíonachta daonna agus roinnt baictéir “cabhracha” atá i ngnáthfhlóra an duine. Mar sin féin, má dhéantar damáiste ar bhealach ar bith don chóras imdhíonachta nó do bhaictéir “mhaith” (mar shampla, ceimiteiripe, VEID (víreas easpa imdhíonachta daonna), nó antaibheathaigh á thógáil chun pataiginí eile a mharú), féadann baictéir phataigineacha a bhí faoi shrian fás agus díobháil a dhéanamh don óstach. Is ionfhabhtuithe faille iad cásanna mar sin.

 

Bíonn roinnt pataiginí ina gcúis le heipidéimí. Ina measc tá an baictéar Yersinia pestis a ba chúis leis an mPhlá Mhór, agus an víreas SARS-CoV-2 ba chúis leis an bpaindéim Covid-19.

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