Abstract. Parasites and bacteria have co-evolved with humankind, and they interact all the time in a myriad of ways. For example, some bacterial infections result from parasite-dwelling bacteria as in the case of Salmonella infection during schistosomiasis.
Parasites are part of a large group of organisms called eukaryotes. Parasites are different from bacteria or viruses because their cells share many features with human cells including a defined nucleus. Parasites are usually larger than bacteria, although some environmentally resistant forms are nearly as small.
A mutually beneficial relationship exists between the human intestine and many of its symbionts: the human intestine provides nutrients to the resident bacteria, whereas bacteria aid in the digestion of food and absorption of nutrients, produce vitamins such as biotin and vitamin K, regulate immune system function, and ...
Sarcodina – the ameba, e.g., Entamoeba. Mastigophora – the flagellates, e.g., Giardia, Leishmania. Ciliophora – the ciliates, e.g., Balantidium. Sporozoa – organisms whose adult stage is not motile e.g., Plasmodium, Cryptosporidium.
Parasitism in Humans
The organisms that parasitize humans include fungi, leeches, lice, viruses, protozoa, tapeworm, etc. Few organisms such as Helminthes live inside the intestine of the host and causes several infectious diseases, such as jaundice, malnutrition, diarrhoea, etc.
A parasitic relationship is one in which one organism, the parasite, lives off of another organism, the host, harming it and possibly causing death. The parasite lives on or in the body of the host.
Parasitism has an extremely wide taxonomic range, including animals, plants, fungi, protozoans, bacteria, and viruses.
Common global water-related diseases caused by parasites include Guinea worm, schistosomiasis, amebiasis, cryptosporidiosis (Crypto), and giardiasis. People become infected with these diseases when they swallow or have contact with water that has been contaminated by certain parasites.
Giardia is arguably the most common parasite infection of humans worldwide, and the second most common in the United States after pin-worm. Between 1992 and 1997, the Centers for Disease Control and Prevention (CDC) estimated that more than 2.5 million cases of giardiasis occur annually.
This is the temperature of the human body. Examples include Listeria monocytogenes, Pesudomonas maltophilia, Thiobacillus novellus, Staphylococcus aureus, Streptococcus pyrogenes, Streptococcus pneumoniae, Escherichia coli, and Clostridium kluyveri.
Humans have evolved intimate symbiotic relationships with a consortium of gut microbes (microbiome) and individual variations in the microbiome influence host health, may be implicated in disease etiology, and affect drug metabolism, toxicity, and efficacy.
When two species benefit from each other, the symbiosis is called mutualism (or syntropy, or crossfeeding). For example, humans have a mutualistic relationship with the bacterium Bacteroides thetaiotetraiotamicron, which lives in the intestinal tract.
Symbiotic relationships
Symbiotic bacteria are able to live in or on plant or animal tissue. In digestive systems, symbiotic bacteria help break down foods that contain fiber. They also help produce vitamins. Symbiotic bacteria can live near hydrothermal vents.
Bacteria and viruses can live outside of the human body (for instance, on a countertop) sometimes for many hours or days. Parasites, however, require a living host in order to survive. Bacteria and parasites can usually be destroyed with antibiotics. On the other hand, antibiotics cannot kill viruses.
Parasitic infections can be spread in a number of ways. For example, protozoa and helminths can be spread through contaminated water, food, waste, soil, and blood. Some can be passed through sexual contact. Some parasites are spread by insects that act as a vector, or carrier, of the disease.
Humans are hosts to nearly 300 species of parasitic worms and over 70 species of protozoa, some derived from our primate ancestors and some acquired from the animals we have domesticated or come in contact with during our relatively short history on Earth.
Bacteria and viruses can live outside of the human body (such as on a countertop) sometimes for many hours or days. But parasites need a living host to survive. Bacteria and parasites can often be killed with antibiotics.
Parasites live in other host organisms and depend on them for survival. Parasites that can affect humans include ticks, lice, and hookworms. Without a host, a parasite cannot live, grow, and multiply.
Finally, eukaryotic parasites may also simply prey upon prokaryotes (e.g., a helminth grazing upon, or an amoeba phagocytosing, gut bacteria).
Parasites may be grouped according to where they live. Ectoparasites, such as fleas and ticks, live on the surface of a host. Endoparasites, such as intestinal worms and protozoa in blood, live inside a host's body. Mesoparasites, such as some copepods, enter the opening of a host body and partially embed themselves.
An example of a parasitism relationship is that of ticks, fleas, lice or leeches on a host such as a human or a dog.