Infectious disease, biological and drug defensesWord count: 2462When a pathogen enters the body, the person becomes infected.Pathogens are a kind of parasite that survives by the energy they use from the host body. In this case, some pathogens have the ability to produce a poison that, if released, can damage your body. Therefore what is a pathogen?Pathogens include bacteria, viruses, proteases and fungi. The larger pathogens like worms, which include smooth worms and roundworms.BACTERIA                                                                                        There are four primary stages in bacterial infections:                            Connect to host cells using piliThe structure of the peel can extend from the level of some bacteria. They are shorter than flagella. They are not movable and live in the bed close to bacteria; Pilli makes them from the protein.DuplicateInvasion of host tissue                                               Destruction of host cells by toxin                                                                                                     (google.com.2018)Salmonella typhi transmitted through food and indirect transmission through contaminated water, meat products. These bacteria produce toxins.The diagrams show a bacteria structure and also possible sites of infection. (Google.com.2018)Thee most common type is campylobacter and also most common cause of food poisoning in the UK. Infection is commonly caused by chicken poultry consumption. Non-pasteurized milk is a common contamination to the birds’ feces.                                                     (Ka-perseus-images.s3.amazonaws.com, 2018) VIRUSESViruses simply do not cause these simple disease, but also aids to AIDS, Ebola, hepatitis and herpes. The diagram shows a bacteriophage a type of viruses. What causes these viruses to be so dangerous and the human immune system sometimes fights against it?The virus consists of the following parts:Nucleic acid: single or double strands of DNA or RNA that contain viral vital information.Protein coverage: protects DNA or RNALipid membrane: protect the protein (it’s found in some specific viruses, such as influenza and they are called sheath viruses).These viruses simply release their content after entering the cell, but viruses that cannot easily pass through the membrane should be injected into the cell with their genetic material tricks. The target receptors on the host cell to gain entry into the cell. They also use enzyme to manipulate the hosts DNA to replicate the virus. The diagram below illustrates the life cycle of virus.