First of all, people and animals suffer from infectious diseases.
Many microorganisms and parasites can cause human and animal diseases. Sick or toxic animals and their excreta, secretions and animal products are the main sources of infection. Some diseases are spread by blood-sucking insects.
1. People and animals spread by poisonous animals will get sick.
Sick animals or asymptomatic carriers can be used as the source of infection. Such as: Escherichia coli O 157:H7, influenza virus.
2. Human and animal diseases caused by biological vectors.
The disease is mainly transmitted by blood-sucking arthropods. Pathogenic microorganisms such as arboviruses propagate in insects, spread vertically through eggs, and spread to animals or people through bites. Some mammals or people become definite hosts after being infected, while others become sources of infection. Such as Japanese encephalitis, dengue fever, Lyme disease (mainly Ixodes as the main vector).
3. Intermediate host mediated human and animal diseases.
Many parasites have complex life histories and usually need one or two intermediate hosts. If people eat the immature intermediate host of parasites containing metacercariae, it will lead to parasitic infection. Such as cysticercosis and clonorchiasis.
Second, human and animal endemic diseases.
Due to the harmful factors of geography, humanities, geology and climate, people and animals will suffer from endemic diseases. Environmental pollution leads to more and more serious chemical poisons such as arsenic and cadmium. For people, animals can be used as indicators of environmental factors, but also as animal models to study human diseases, such as endemic goiter and endemic fluorosis.