Scientists believe that this variability comes from both genetic and environmental factors within the host. This is described as context-dependent pathogenicity. Pathogenic variability in hosts Īlthough pathogens do have the capability to cause disease, they do not always do so. This can be seen in the unicellular Plasmodium falciparum parasite which causes malaria in humans. Parasitism occurs when the pathogen benefits from the relationship while the host is harmed. Many of the bacteria aid in the breaking down of nutrients for the host and, in return, our bodies act as their ecosystem. Mutualism occurs when both the pathogen and the host benefit from the interaction, as seen in the human stomach. An example of this is Bacteroides thetaiotaomicron, which resides in the human intestinal tract but provides no known benefits. Commensalism is when the pathogen benefits while the host gains nothing from the interaction. Context-based host interactions Types of interactions ĭepending on how the pathogen interacts with the host, it can be involved in one of three host–pathogen interactions. Eventually, it gets reactivated and enters the lytic cycle, giving it an indefinite "shelf life" so to speak. The lysogenic cycle, however, is when the viral DNA is incorporated into the host genome, allowing it to go unnoticed by the immune system. Many times, viral pathogens enter the lytic cycle this is when the virus inserts its DNA or RNA into the host cell, replicates, and eventually causes the cell to lyse, releasing more viruses into the environment. Upon entry into the host, they can do one of two things. Viruses, however, use a completely different mechanism to cause disease. pylori, can secrete toxins into the surrounding tissues, resulting in cell death or inhibition of normal tissue function. This causes an immune response, resulting in common symptoms as phagocytes break down the bacteria within the host. Microbes and fungi cause symptoms due to their high rate of reproduction and tissue invasion. Within the host, pathogens can do a variety of things to cause disease and trigger the immune response. Aspergillus the most common pathogenic fungi, secretes aflatoxin, which acts as a carcinogen and contaminates many foods, especially those grown underground (nuts, potatoes, etc.). HIV and hepatitis B are viral infections caused by blood-borne pathogens. Many pathogenic bacteria, such as food-borne Staphylococcus aureus and Clostridium botulinum, secrete toxins into the host to cause symptoms. This includes the following: food borne, airborne, waterborne, blood-borne, and vector-borne. Pathogens include bacteria, fungi, protozoa, helminths, and viruses.Įach of these different types of organisms can then be further classified as a pathogen based on its mode of transmission. coli, which have allowed scientists to develop antibiotics to combat these harmful microorganisms. Since then, many other organisms have been identified as pathogens, such as H. Giardia lamblia was discovered by Leeuwenhoeck in the 1600s < but was not found to be pathogenic until the 1970s, when an EPA-sponsored symposium was held following a large outbreak in Oregon involving the parasite. Most of these findings went unnoticed until Robert Koch rediscovered the organism in 1884 and linked it to the disease. He described how it causes diarrhea as well as developed effective treatments against it. His initial findings were just drawings of the bacteria but, up until 1880, he published many other papers concerning the bacteria. One of the first pathogens observed by scientists was Vibrio cholerae, described in detail by Filippo Pacini in 1854. Viruses can also infect the host with virulent DNA, which can affect normal cell processes ( transcription, translation, etc.), protein folding, or evading the immune response. On the molecular and cellular level, microbes can infect the host and divide rapidly, causing disease by being there and causing a homeostatic imbalance in the body, or by secreting toxins which cause symptoms to appear. Because of this, the definition has been expanded to how known pathogens survive within their host, whether they cause disease or not. This term is most commonly used to refer to disease-causing microorganisms although they may not cause illness in all hosts. The host–pathogen interaction is defined as how microbes or viruses sustain themselves within host organisms on a molecular, cellular, organismal or population level.
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