Station 2: Supergroup Excavata

The diplomonads (Greek for "two units") are a group of flagellates, most of which are parasitic. They include Giardia lamblia, which causes giardiasis in humans.

Most diplomonads are double cells: they have two nuclei, each with four associated flagella, arranged symmetrically about the body's main axis. They lack both mitochondria and Golgi apparatuses. However, they are now known to possess modified mitochondria, in the case of G. lamblia, called mitosomes. 

Species: Giardia lamblia

Giardia infection (Giardiasis) is an intestinal infection marked by abdominal cramps, bloating, nausea and bouts of watery diarrhea.  Giardia infection is caused by a microscopic parasite that is found worldwide, especially in areas with poor sanitation and unsafe water.

Giardiasis is one of the most common causes of waterborne disease in the United States. The parasites are found in backcountry streams and lakes but also in municipal water supplies, swimming pools, whirlpool spas and wells. Giardia infection can be transmitted through food and person-to-person contact.

Giardia infections usually clear up within a few weeks. But you may have intestinal problems long after the parasites are gone. Several drugs are generally effective against Giardia parasites, but not everyone responds to them. Prevention is your best defense.

Parabasalids are typical excavates in that they are unicellular, anaerobic and are flagellated.  It is different in that it has a modified golgi apparatus at the base of its flagella (you won’t see it in the microscope).  One of the best known examples of a parabasalid is the protist that cause the sexually transmitted disease as trichomoniasis or “trich”.  The species of bacterium that inhabits the lower genital regions of all sexes is called Trichomonas vaginalis.

Species: Trichomonas vaginalis

Trichomonas vaginalis is an anaerobic, flagellated protozoan parasite and the causative agent of trichomoniasis. It is the most common pathogenic protozoan infection of humans in industrialized countries. Infection rates are similar between individuals with female reproductive systems and those with male reproductive systems. Symptoms are more commonly reported in the former, while infections in the latter are often asymptomatic.

Most of the members of this clade are free-living species and have one long flagellum used in locomotion along with a second, shorter one.  Many of the members of this group are heterotrophic but some are also mixotrophic (can be heterotrophic or autotrophic) and so can use photosynthesis as a source of energy depending on the environmental conditions.

Genus: Euglena

Euglena is a genus of single cell flagellate eukaryotes. It is the best known and most widely studied member of the Euglenozoan clade, a diverse group containing some 54 genera and at least 800 species. Species of Euglena are found in freshwater and salt water. They are often abundant in quiet inland waters where they may bloom in numbers sufficient to color the surface of ponds and ditches green (E. viridis) or red (E. sanguinea).

The species Euglena gracilis has been used extensively in the laboratory as a model organism.

Most species of Euglena have photosynthesizing chloroplasts within the body of the cell, which enable them to feed by autotrophy, like plants. However, they can also take nourishment heterotrophically, like animals. Since Euglena have features of both animals and plants, early taxonomists, working within the Linnaean two-kingdom system of biological classification, found them difficult to classify. 

Below is a video of a slide of Euglena showing their movement and the movement of their flagella.  Take note on how the flagellum causes the organism to wobble and rotate.  This is often a characteristic that will help differentiate a euglenid from a ciliate (e.g. paramecium) which have much smoother gliding movement.

Genus: Trypanosoma

Trypanosoma is a genus of unicellular parasitic flagellated protozoa. The name is derived from the Greek trypano- (borer) and soma (body) because of their corkscrew-like motion. Most trypanosomes are heteroxenous (requiring more than one obligatory host to complete life cycle) and most are transmitted via a vector. The majority of species are transmitted by blood-feeding invertebrates, but there are different mechanisms among the varying species. Some, such as Trypanosoma equiperdum, are spread by direct contact. In an invertebrate host they are generally found in the intestine, but normally occupy the bloodstream or an intracellular environment in the mammalian host.

Trypanosomes infect a variety of hosts and cause various diseases, including the fatal human diseases sleeping sickness, caused by Trypanosoma brucei (formerly called Trypanosoma gambiense), and Chagas disease, caused by Trypanosoma cruzi.

• Examine the blood smear images below from an individual with trypanosomiasis (Both T. brucei [gambiense] and T. cruzi).  

  • • Make sure to note the following structures in the slides: White Blood Cells, Red Blood Cells, Trypanosome parasite

• Be able to identify the supergroup, clade and species name of both Trypanosoma brucei and T. cruzi.

• Be able to identify the vectors of the different forms of trypanosomiasis.

Trypanosoma brucei - Sleeping Sickness - This is primarily a tropical disease spread by the bite of an infected tsetse fly (genus Glossina). Initially, the first stage of the disease is characterized by fevers, headaches, itchiness, and joint pains, beginning one to three weeks after the bite. Weeks to months later the second stage begins with confusion, poor coordination, numbness, and trouble sleeping. Diagnosis is by finding the parasite in a blood smear or in the fluid of a lymph node.

Trypanosoma cruzi - Chagas disease - This is primarily a tropical disease but is also common in the southern half of the United Stades and It is spread mostly by insects known as "kissing bugs" (this is a group of true bugs known as assassin bugs). The symptoms change over the course of the infection. In the early stage, symptoms are typically either not present or mild, and may include fever, swollen lymph nodes, headaches, or swelling at the site of the bite. After four to eight weeks, individuals enter the chronic phase of disease, which in most cases does not result in further symptoms. Up to 45% of people develop heart disease 10–30 years after the initial infection, which can lead to heart failure. Digestive complications, including an enlarged esophagus or an enlarged colon, may also occur in up to 21% of people, and up to 10% of people may experience nerve damage.