Pathogenic Protozoa

Phylum Euglenozoa
All organisms in this group are flagellated with crystalline rods.  They are only capable of asexual reproduction which is carried out through binary fission.

Class Kinetoplastida
Organisms in this group possess a single, large mitochondrion with a dark staining body inside, the kinetoplast.  Many within this group contain an undulating membrane.
Trypanosoma cruzi
T. cruzi is the parasitic agent of Chagas' Disease and is found in Central and South Africa.  It is transmitted to its human definitive host through its kissing bug vector.  Upon landing onto a susceptible host, the kissing but bites and defecates on the skin releasing the infective tryptomastigote stage.  Scratching the wounds allows the parasite to enter the person's blood stream where they invade and lyse host reticuloendothelial cells of the spleen, liver, lymph nodes, and muscles.  Initially, an acute infection is characterized by a chagoma, or localized swelling, produced by the invasion of lymph cells.  As the number of T. cruzi invading host cells increases, an infected person can experience weakness, fever, neurological disorders, tachycardia, myocarditis, which eventually leads to heart failure.  Chronic infections have a much slower onset and specifically target the muscles.  70% of deaths by chronic infections in endemic areas are caused by heart failure due to cardiomegaly or ventricular aneurisms.

Phylum Apicomplexa
This Phylum consists of parasitic alveolates characterized by the possession of an apical complex at some stage in their life cycle.

Class Coccidea
Class Coccidea is consists entirely of endoparasites of vertebrates and invertebrates.  Their life cycles all involve intracellular reproduction causing significant pathology with three distinct phases, schizogony, gamogony, and sporogony.
Toxoplasma gondii
T. gondii is found throughout the world in many different countries and cultures.  This parasite has two host life cycles.  In the definitive host, typically cats, it is found in the intestinal cells and is relatively harmless to the cat.  However, when T. gondii is in its mouse intermediate host, a significant amount of damage occurs due to the invasion and production of cysts in the muscles, heart, and brain tissues.  Infection of the intermediate host also causes behavioral modifications which make the mouse more susceptible to predation.  Humans can acquire this infection by ingesting oocysts from cat feces or undercooked, infected livestock.  In a healthy person, an infection results in flu-like symptoms and swelling of the lymph nodes, but is soon suppressed by host immune system.  Infections in an immunocompromised individual can result in encephalitis, ocular toxoplasmosis, and myocarditis.  Additionally, if a pregnant woman with no prior exposure becomes infected, T. gondii can travel across the placenta and infect the fetus causing congential toxoplasmosis and can result in severe damage to the fetus' central nervous system.

Plasmodium falciparum
P. falciparum is the agent responsible for Malignant Tertian Malaria which is the most common and virulent species of malaria.  It occurs in tropical zones where it is the leading cause of death.  Fortunately, it has been eradicated from the United States and Mediterranean areas.  It is transmitted to humans by the Anopheles specie of mosquito.  Once in the blood, the merozoites infect host red blood cells, reproduce, and then emerge every 24 to 48 hours.  The pathogenicity is caused by these cycles of schizogony, known as paroxysm, in which there is a sudden increased intensity of the disease and because of the high parasitemia of this particular species.  The merozoites and their waste products enter the host circulation activating the host inflammatory response causing extreme headaches, fevers up to 104-106 degrees F, intense chills, nausea, and vomiting.  The rupturing of red blood cells causes the urine to become black or purplish from residual hemoglobin and thus, the condition is termed Black Water Fever.  Additionally, cerebral malaria can occur in which the red blood cells become sticky, and clot within the small capillaries of the brain.  The clogged vessels ultimately rupture, causing stroke and pulmonary edema.

Phylum Amoebozoa
The Amoebozoans are characterized by the use of lobe-shaped pseudopods for locomotion and to engulf food.  Many are endocommensals or endoparasites, living in the digestive tracts of arthropods and vertebrates.
Naegleria fowleri
N. fowleri is a free-living amoeba found in soil or water.  It is an opportunistic pathogen in humans that causes Primary Amoebic Meningoencephalitis.  While infections are rare, less that 3 cases a year, they are always fatal as there is no cure for the infection.  Infection occurs when N. fowleri enters its host through the nasal mucosa where it follows the nerves that lead to the brain.  There the amoeba invades the brain tissues and lyses its cells.  Initial symptoms are headache, fever, vomiting, and stiff neck.  The symptoms quickly progress to dizziness, hallucinations, seizures, coma, and death occuring between 7 and 14 days.