Blaida Cervantes, MMI 133 Microbe Assignment

Amebiasis

Key points

Amoebiasis, also known as Amoebic dysentery is a disease caused by pathogen Entamoeba histolytica, that is spread in places with poor sanitation that allows contamination of drinking water and food with fecal matter. Entamoeba is an obligate intracellular parasite of the human gastrointestinal tract.
E. histolytica exists in two subdivided forms; infection with E. histolytica can induce diarrhea and extra-intestinal illness, while E. dispar is regarded as a safe commensal.
E. histolytica are anaerobe parasite that get their nutrition from another living thing (their host). The host organism is the parasite's sole source of sustenance. In the host, parasite eggs mature into fully formed cysts.
The World Health Organization (WHO) estimates that 500 million people around the world may be infected with Entamoeba; however, only 10% of these people have the species E. histolytica, while the remaining 90% have other nonpathogenic species. Amoebiasis is the fourth highest cause of death owing to a protozoan infection, responsible for 40,000-100,000 fatalities annually.

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Classification of Amoebiasis-causing E. histolytica

Entamoeba histolytica is a pseudopod-forming protozoan that belongs to the phylum Amoebozoa and class Archamoebae. Archamoebae are distinct from other species of Amoebozoa in that they do not include mitochondria in their cells. Therefore, species that belong to the Archamoebae are species that are capable of anaerobic respiration. E. histolytica is part of genus Entamoeba, and species E. histolytica and domain Eukarya.

Fritz Schaudinn (1903) chose the name E. histolytica because of its potential to produce tissue lysis, as its name suggests (histo–lytic = tissue destroying).

Biology and Lifecycle

E. histolytica is monogenetic and completes its life cycle solely in humans. When individuals ingest fully developed cysts that contain four nuclei, those cysts go through the intestines without being impacted by the stomach fluids, but they can be digested by the trypsin found in the intestines. Excystation takes place in the small intestine, resulting in the release of trophozoites, which then go to the large intestine. The trophozoites reproduce via binary fission and generate cysts, which are excreted in the faeces. As a result of the protection provided by their walls, cysts can survive days to weeks in the external environment and are responsible for disease transmission. In some people, the trophozoites invade the intestinal mucosa or, via bloodstream, extraintestinal sites like the liver, brain, and lungs (extraintestinal disease), causing pathological symptoms. It has been proven that the invasive and noninvasive forms are two different species, E. histolytica and E. dispar, but not everyone who has E. histolytica will get serious infections. The appearance of these two species is the same. Transmission can also happen through sexual contact with faeces (in which case not only cysts, but also trophozoites could prove infectious).

image reference: https://www.cdc.gov/dpdx/amebiasis/modules/Amebiasis_LifeCycle_lg.jpg

Geographical distribution

E. histolytica is more abundant in tropical and subtropical regions than in cooler climates. Additionally, it is believed that E. histolytica is responsible for more deaths around the world than any other parasitic illness, with the exception of malaria and schistosomiasis.

Mode of transmission

E. histolytica is transmissible between hosts via the fecal-oral route of contamination. Sexual transmission is also a possibility. Men who have sex with other men, tourists, recent immigrants, immunocompromised individuals, and institutionalised populations are at danger in industrialised nations.

Pathogegenesis of Amebiasis

Amebiasis is passed from person to person through feces-to-oral contact, such as by drinking contaminated water or swimming in it. On the other hand, systemic amebiasis usually doesn't show up until after the parasite has already colonized in the colon. During an infection, the parasite will make extracellular proteinases and a number of other substances that make it more dangerous. After attaching to the target cell, the trophozoite form releases a protein that damages the host cell's membrane. Most of the time, only a small amount of damage is done to the host's cells, and the host shows no symptoms at all. E. histolytica can create a portal in the mucosa of the intestine. This makes it easier for other pathogens, like bacteria and viruses, to get into the body and spread to other parts.

After going through the stomach, the cyst makes its way to the small intestine. Here, the cyst membrane breaks, letting out a parasite with four nuclei that splits into four trophozoites. These trophozoites move to the colon, where they damage the epithelial cells that line the colon and cause small mucosal ulcers. In rare cases, lesions can form in the brain, liver, or spleen, and abscesses can form in these areas.

Symptoms

Amebiasis doesn't always cause illness. Initially, you may not have amebiasis symptoms. Four weeks after infection, symptoms may appear. Cramping, diarrhea (occasionally with rectal bleeding), fever, loose stools (amebiasis stool colour may not alter, but stools may be watery), and nausea are the most common symptoms. Even without symptoms, E. histolytica can live in your intestines for a long time. If you've visited an unsanitary place, contact your doctor about testing.

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Dagnosis and Treatment

Diagnosis

Confirmation of the diagnosis can be accomplished through the discovery of Entamoeba histolytica antigen or DNA in the patient's feces, or antibodies against the parasite in the blood serum.

Treatment

The treatment consists of nitroimidazoles, such as metronidazole or tinidazole, and then luminal medicines, such as paromomycin or diloxanide furoate, are administered to prevent relapse after the initial treatment. In areas where the disease is prevalent, reinfection is common; patients should be counselled on ways to lower their chances of contracting the disease again.

Metronidazole

The trophozoites of Entamoeba histolytica that are present in the intestines and tissue are eliminated by metronidazole, while the cysts that are present in the intestines remain. It would indicate that cells are able to absorb it. Compounds that are intermediate in their metabolism are generated, and they bind to DNA and block protein synthesis, both of which lead to the death of cells. It's possible that the creation of free radicals is responsible for the antimicrobial effect. In cases of invasive amebiasis, the use of metronidazole is recommended.

Tinidazole

Tinidazole is a 5-nitroimidazole derivative that is used as a treatment for infections caused by susceptible protozoa. It is unknown how it exerts its anti-Giardia and anti-Entamoeba effects on different types of Entamoeba. Tinidazole is prescribed for the treatment of intestinal amebiasis and amebic liver abscess in patients aged 3 years and older, including adults. These conditions are caused by the bacteria E histolytica.

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How do we prevent E. hystolytica?

Amoebiasis can be avoided by taking these measures around the house:

After using the restroom or changing a baby's diaper, wash your hands for 15 seconds with hot soapy water.
It's important to keep the restrooms clean. Toilets and sinks require special care.
Don't use each other's washcloths or towels.

When making food, people who work with food should make sure:

The hands are washed well with soap and hot, running water. Dry your hands with a paper towel or a blow dryer.
The raw vegetables should be washed well and cooked.
Reheated food has an internal temperature of at least 75°C.

When travelling in developing countries:

Avoid raw foods, especially unpeeled vegetables and fruit.
Only drink packaged drinks, boiling or chlorinated water.
Avoid ice-filled drinks.
Cook it, peel it, or leave it.

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