Bacterial and viral diseases

Bacterial diseases: Although thousands of bacterial species exist, only a small number are pathogenic to humans. These bacteria often act by releasing toxins that damage host tissue. They spread through air, contaminated water, inhaled droplets/aerosols, or by sharing utensils and clothing with an infected person. Table 7.1 lists eight common bacterial diseases — shigellosis (bacillary dysentery), bubonic plague, diphtheria, cholera, tetanus, typhoid, pneumonia and tuberculosis — each with its own causative species, site of infection, transmission route and symptom pattern. Typhoid, for instance, is confirmed clinically using the Widal test. A recurring public-health concern is antibiotic/bacterial resistance: overusing or misusing an antibiotic (skipping doses, using it for viral infections like the common cold, or treating minor infections that the immune system would clear on its own) allows some bacteria to evolve resistance, making the infection harder to treat in future. It is also worth noting that freezing does not kill bacteria — it only halts their growth, so they can resume multiplying once conditions warm up again. …