Posts tagged protozoa

Death by “Marsh Fever” (Malaria)

More people die of malaria every single day than have died of Ebola in the past decade.

During an average year, more people die of influenza every month than have ever even been infected with Ebola.

This is because mosquito and airborne transmission are far more effective than direct bodily-fluid contact. It’s fairly simple to eliminate bodily fluid transmission in countries with ready access to chlorine and water. Mosquito bites and airborne droplets are almost impossible to eliminate - all we can hope to do is control them.

There are much scarier things out there than Ebola.

Malaria" by Giulio Aristide Sartorio, 1905 (top), 1883 (bottom).

Parasites in History: General Overview - Endoparasites

Humans are afflicted by a number of diseases caused by parasitic protozoa and helminth worms. The first records of these ancient associations come from studies on archeologic material and the writings of the Greek, Egyptian, and Roman empires, but it was not until the theory of spontaneous generation had been disproved in the nineteenth century that it became possible to incriminate parasites in the etiologies of a number of diseases that had long plagued mankind.

The golden age of parasitology was the nineteenth century, when most of the life cycles of parasites were accurately described for the first time. 

As an overview, here are a few of the most commonly written-about parasites in history. Keep in mind, the microscopic parasites (mostly the protozoa) were not known, in that they were not seen in those that perished from the subsequent diseases, but they were known for the diseases they caused; malaria, amoebic dysentery, and giardia are all protozoan parasitic diseases that have killed millions throughout history.

Ticks, fleas, lice, and scabies are all ectoparasites, meaning that they live outside the body or just within the skin. They can be incredibly dangerous, thanks to the bacteria and viruses they can transmit. I’ll cover those in a bit! For now, here are some most common endoparasites.

Endoparasites - Parasites that cause infection inside the body.

Plasmodium spp.: Protozoan - Eleven species that infect humans (four significant species), causes malaria, transmitted by Anopheles spp. mosquitoes.

Schistosoma spp: Flatworm - Causes schistosomiasis (also known as bilharzia), which, while rarely fatal, can cause chronic illness and organ damage, cause genital sores (increasing susceptibility to HIV), as well as abdominal pain and diarrhea. There are descriptions of schistosomiasis-like diseases as long ago as the early Greek/late Egyptian writings.

From Invertebrate Anatomy. R. D. Barnes, 1980.

Strongyloides spp: Roundworm - Commonly known as “hookworm”. Was the chief cause of the “lazy Southerner” phenomenon. Infection can cause anemia, dysentery, and hemorrhage. Infection in children is particularly problematic, as it causes drastically increased absences from school, learning disabilities, and slowed motor function development - this sort of childhood leads to unproductive adults.

From Archive of images under Creative Commons License

Ascaris lumbricoides: Roundworm - Known as the “giant intestinal roundworm”. Lives in the small intestine and feeds upon chyme. Ascariasis is the most common helminth infection of humans, and while often asymptomatic for years, it can cause extreme symptoms and even death when symptoms manifest. 

From Ascariasis Summary

Guinea Worm: Roundworm - Caused by Dracunculus medinensis and causes “Guinea Worm disease” (GWD) (also known as dracunuliasis - from a Latin term meaning “affliction with little dragons”). Lives within the bloodstream, and is transmitted through contaminated water.

From Canadian Medical Association Journal archives

Tapeworm: Flatworm - We all known tapeworms, right? There are several species of Cestoda that infect humans, mostly coming from under-cooked meat products. Generally inhabits the intestine, but can sometimes (especially pork tapeworms - Taenia solium) encyst within muscle tissues, and eggs can even pass blood-brain barrier. If the body doesn’t destroy the small larvae within the brain, they encyst and cause horrible swelling and destruction of areas of the brain. Don’t worry, that kind of infection is incredibly rare in general, but is practically uneheard when you fully cook or don’t eat pork (and don’t have a maid/cook who already has tapeworms - interesting story, will go into it later)

From, the Wikimedia Commons Archive

Entamoeba: Protozoan - Causes amoebic dysentery and amoebic liver cysts, and is transmitted by contaminated water. Caused at least several hundred deaths along the “Oregon Trail” (well, it was along all the migration trails, even the drier trails to California). Entamoeba histolytica is the species that causes amoebiasis. Don’t confuse Entamoeba coli with Escherischia coli! The former is a protozoan, while the latter is what common culture knows as “E. coli”.

United States Center for Disease Control Graphic - E. histolytica life cycle

Giardia: Protozoan - The giardia are creepy little guys. They’re flagellated protozoans that swim/stick themselves down in the intestines and cause giardiasis. One becomes infected with giardia by ingestion of fecal material or contaminated soil. Though they can cause extreme abdominal cramps, diarrhea, and gas, giardiasis does clear up on its own after 2-6 weeks. What one has to avoid is re-infection…since giardia can be free-swimming, they can survive within water sources on their own, without a problem. That’s why outbreaks in small communities without the ability to sanitize water do not cease without education about boiling water, or intervention leading to sanitized water comes around.

Giardia populating a gerbil intestine: National Institute of Health (NIH) scanning electromicrograph image 

The four main malarial species of Plasmodium.

Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, Plasmodium vivax (clockwise).

Mortality Rates:

1. P. falciparum - By far the most deadly, also the most common

2. P. vivax - Death comparatively uncommon, but relapse is common; unlike P. falciparum, P. vivax and P. ovale both have life stages where they reside in the liver - radical treatment is required to get rid of those and prevent relapse.

3. P. ovale - The most uncommon. Not terribly deadly, but also has a relatively high relapse rate.

4. P. malariae - Almost never kills, but is a nuisance. Only about 4% of cases in most areas. Can be differentiated from the others because it has a quartian fever (every fourth day), instead of tertian (every third day). 

Historic Malaria

Malaria has plagued humans ever since we became, well, humans. Or, at least since we became non-nomadic agricultural humans. About 10,000 years ago, malaria started emerging as a significant cause of human mortality. Thus began the natural selection towards “sickle-cell” and two other blood conditions that, while potentially harmful when homozygous for the trait, give significant advantages against malarial infection when the person is heterozygous for the trait.

Malaria has been written about since 2700 BCE, in an old Chinese medical manuscript. It’s one of the few diseases that doesn’t really have any periods of time where it’s completely absent from known writings…it was throughout the tropical and subtropical world and a very persistent affliction.

Malaria is not a bacteria like it was thought to be for a long time (well, since bacteria were known). It’s now known to be protozoan. Given that protozoa are self-motile eukaryotic organisms, malaria is actually a parasitic infection.