People do not have immunity to intracellular animal pathogens (chlamydia, estimated up to 350 different species), which do not merge peacefully, in the human body. The pathogens quickly infect host cells, depleting energy inside the cells; infect monocytes and macrophages (the immune system), weakening the immune system and spreading pathogens; generate inflammation from the immune system attack; generate harmful debris, which can alter genes; and disrupt function. Immortal pathogens start a cascade of events which alter the microbiome and mycobiome, foster development of pathologic fungus, and lead to chronic disease.
Animals are an infectious vector—pathogens can be transmitted from animals-to-people, and from people-to-animals. Animal pathogens can impact the health of the mother during pregnancy, cross the placenta to infect a fetus, and infect young children. Pregnant women are advised to avoid cat litter, to avoid the risk of toxoplasmosis acquired in utero. Remaining vigilant about the health of pets and animals, and good hygiene around to pets and animals, is necessary to minimize health risks to people.