Unit 2 Microbiology Exam Chap 9

parasitology: study of organisms that live at the expense of their host pathogen: a parasitic organism that causes disease

If you looked at these relationships over long periods of time, you would see that parasites tend to become more adapted to and less destructive of their hosts.

A biological vector internalizes the parasite in between hosts. For example, the disease malaria is caused by a protozoan parasite Plasmodium vivax. The biological vector which transmits the parasite from host to host is the Anopheles mosquito. When a mosquito bites a person with malaria, it can pick up the parasite and internalize it before transmitting it to a new host. A mechanical vector is a vector which physically or mechanically transfers a parasite from place to place. For example, imagine an ant crawling across dog "droppings" at the park and then across your picnic. If those droppings contained bacteria such as E. coli, they could be mechanically transferred to your food in this way.

The Kingdom Protista contains unicellular, eukaryotic microorganisms. Many of these them are colonial, meaning they will often associate with one another to form a colony and divide the labor of the group. They are classified by their means of locomotion: some have pseudopodia, some have flagella, some have cilia and some have no means of locomotion.

They are significant to our study of microbiology as they play a crucial role in the food chain. They tend to consume members of the Kingdom Monera and are then consumed by larger, more complex organisms. In this way they participate in the "circle of life" of all living things in the environment.

Protists are also significant as many of them are pathogens causing diseases such as Malaria, Dysentery or Toxoplasmosis

The Kingdom Fungi contains unicellular yeasts and multicellular molds. Some are considered saprophytic, living on decaying matter, such as the fungi that grow on the decaying plant material in on forest floor. Some are considered truly parasitic, living at the expense of hosts that they infect. Fungi reproduce asexually by budding as well as sexually by producing spores. They are classified based on the types of spores they produce.

Fungi are significant to our study of microbiology for several reasons. They play a role in the "circle of life" by serving as decomposers. By breaking down dead matter, they replenish the soil so that soil-borne microorganisms will have nutrients and provide nutrients for plants to grow. They are also significant as natural producers of antibiotics. Remember the first antibiotic to be discovered by Alexander Flemming was penicillin, produced by the Penicillium mold.

There are a variety of diseases caused by yeasts and molds known as mycoses. Yeasts such as Candida can cause diseases such as thrush or athlete's foot. Molds can cause severe respiratory diseases or even encephalitis.

Helminths include the flatworms and the roundworms. They are bilaterally symmetrical so that if you drew a vertical line down their middle there would be a mirror image on each side. They also have anterior ends with nervous tissue or a primitive brain at one end. They have a posterior end with a place for the waste to exit.

There are many medically important helminths. Trichinella spiralis causes trichinosis which can be contracted from eating undercooked pork. Dirofilaria immitis is the cause of heartworms in dogs. Elephant Man's Disease, caused by a Wucheria bancrofti infection, causes massive swelling in the lymph nodes which cannot drain properly due to the presence of these roundworms.

Arthropods are the largest group of organisms. They are characterized as having jointed exoskeletons, segmented bodies and jointed appendages. They are classified based on the number of appendages: arachnids have eight legs and insects have six legs.

Arthropods are relevant to our study of parasitology as many serve as vectors of disease transmission. Ticks, for example, can transmit viruses leading to encephalitis or the bacterium causing Lyme disease. Fleas can transmit the bacterium responsible for the Black Plague. Mosquitos can transmit the protozoan parasite responsible for Malaria or the virus which causes West Nile Fever.

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