Micro Exam #3 Ch. 12

Nematodes (roundworms)

Nematodes or roundworms are characterized by an unsegmented, cylindrical body exhibiting bilateral symmetry; they look like earth worms. (fig 12.27) They have digestive, nervous and reproductive systems, but an excretory systems is not found in all members. The sexes are usually seperate. A protective covering over the worm's body, called a cuticle, offers protection from digestion by the host. (Most nematodes are ingested reside in the host's digestive tract, exposed to digestive enzymes and chemicals.) Some have cutting plates and/or hooks at the mouth to facilitate tissue adherence.

FUNGI

Organisms which are classified as fungi are characterized by being chemoheterotrophic saprophytes; organisms which directly absorb organic nutrients through the plasma membrane (they do NOT have mouths). The organic nutrients are often derived from dead and decaying organisms and the fungi produce extracellular enzymes which help to degrade macromolecules to smaller molecules which can be transported across the cell membrane. Virtually all members have a cell wall (composed of chitin or mannin). Both single and multicelled forms exist. There are 3 major divisions; mushroom, yeast, mold. We will not describe the mushrooms because they do not produce human disease by active growth in a host. (Mushrooms do produce toxins which cause disease if ingested.)

Wuchereria bancrofti (elephantiasis)

Lymphatic inflamation, edemia, chills, fever, inflamation of testes, thickened and cracked skin (due to toxin release and immune response to it); mosquito bite (immature larvae) -> bloodstream -> lymphatic system (adults reproduce) -> immature larvae -> bloodstream (ingested by mosquito).

Fungal Classification

based on nature of sexual stage Fungi imperfecti (Deuteromycota): no sexual stage has been observed (only asexual). Pathogens usually found in this group.

Clonorchis (Opisthorchis) sinensis (chinese liver fluke); Clonorchiasis

abdominal pain, diarrhea, enlarged spleen and liver; penetration of skin by free swimming larval form -> migration to liver (maturation & reproduction) -> eggs migrate to intestine and are excreted with feces -> in water, seek and penetrate intermediate host (often snail) where larval stages occur]

Cryptosporidium

causes severe diarrhea, abates within 2 wks in healthy hosts, but persists in immune compromised individuals. Infection is through ingestion of fecally contaminated food or water.

Bacterial diseases:

Fleas: plague; Ticks: Lyme disease

Flatworms tapeworms & flukes; platyhelminths

Flatworms have flattened bodies. One subgroup, tapeworms, have a segmented body exhibiting bilateral symmetry. The other subgroup, flukes, have unsegmented bodies. Flatworms have either an incomplete digestive system (the same opening serves as mouth and anus) or they have no digestive system at all (tapeworms absorb nutrients from the host directly across their body wall). They have adhesine organs for attachment to the host such as the suckers (suction cups) on the scolex of tapeworms. Most members exhibit excessive reproductive capacity to insure survival of some progeny. In addition, tapeworms are hermaphroditic (both sexes are present in one individual). Each individual segment of the worm, called a proglottid, contains both male and female reproductive organs. The worm can self fertilize to generate proglottids which contain hundreds of eggs. Flatworms also have an external cuticle for protection from the environment inside the host. Flukes have a complex life cycle usually with 4 larval stages. The development of these larval stages usually occurs in fresh water snails.

HELMINTHS

Helminths are multicellular, differentiated, eucaryotic worms belonging to the Animal Kingdom (Kingdom Animalia). Many are macroscopic in size (some tapeworms are 100 feet long). Like most animals, they posses organ systems which form nervous, excretory and digestive systems. Most are free-living, being found in aquatic and soil environments. However, there are many parasites which cause serious human diseases. Helminths are major pathogens. It has been estimated that more than one-third of the worlds population suffers from some helminthic infection. Ingestion is the primary route of infection for most helminths. Helminths can be divided into two groups:

Necator americanus (hookworm)

Hookworm; iron deficiency, anemia, abdominal pain, protein deficiency, lowered antibody response, potbelly in children; larvae penetrate skin (feet), enter blood stream -> lung & heart-> small intestive (maturation & reproduction) -> feces (larvae)

Systemic mycoses

Infections of internal organs and tissues. Many are respiratory infections. These mycoses are often limited in their geographic distribution to certain areas in which the fungus grows in a non-parasitic state in the environment. Those individuals with weakened immune systems are often at higher risk of infection. Specific examples: a. Coccidioidomycosis (valley fever): Caused by inhaling dust which contains fungal spores of the organism Coccidioides immitis. This fungus can exist as a free-living organism which grows well in the acidic soil of the central valley in California. However, if inhaled it will grow as a parasite in the lungs of a human host. It causes flu-like symptoms which can become life-threatening if the organism disseminates (spreads) throughout the body. This organism also causes direct damage to host tissues. b. Histoplasmosis: Caused by Histoplasma capsulatum. Is widespread but occurs often in certain geographic areas. May affect one or more organs, in addition to respiratory tract.

Superficial mycoses

Infections of surface tissue or the mouth region. Usually a variety of fungi can cause each disease. Specific examples: A. Tinea is the name given to a fungal skin infection. A large number of different fungi can actually cause this disease which is often given the common name ringworm (the disease was originally thought to be caused by a worm). In tinea the fungus causes direct damage to host tissue by essentially feeding on the skin. Various types of tinea exist, differing primarily in the tissue infected. 3. Tinea capitis: Scalp and hair follicles infected 2. Tinea pedis (athletes foot): infection of feet B. Candidiasis (also called oral thrush) is caused by Candida albicans. This is a disease characterized by growth of the fungus in the mouth and throat of the host. This organism is an opportunistic pathogen. It normally grows very slowly in a variety of locations on and in the human body without causing disease. However, if the host environment alters to make conditions more favorable for Candida growth it will take the opportunity to reproduce. This extensive proliferation results in disease. Several conditions favor growth of Candida:; all suppress or diminish a host's immune system. Diseases such as AIDS can weaken the immune system. Pregnant women and the aged are also susceptible to thrush. Elimination of the normal bacterial flora of a host by antibiotic therapy will also give Candida a chance to expand into the unoccupied environments in the host. Fig 21.16

Dimorphism

Many fungi exist in two morphologies; a mold-like, multicelled, filamentous stage which reproduces through spore formation and a yeast-like stage where cells grow as individuals and reproduce by budding. These two morphologies may vary greatly. (Indeed, many dimorphic fungi were originally classified as separate mold and yeast.) (fig 12.4) The transition from filamentous to yeast-like growth is usually triggered by som environmental change; change in temperature or nutrient source.

Molds

Molds can be characterzed as multicelled fungi. They exhibit differentiation of cells to produce specialized tissues. Most molds consist of hyphae (tubular branchihg cells) which form long filaments. Hyphae are subdivided by septa which contain pores large enough to permit the passage of nuclei and cytoplasm. Hyphae can branch and fuse to form a large mass referred to as a mycelium (analogues of bacterial colonies) (fig 12.2). Reproductive units called spores are formed by one specialized tissue type referred to as the aerial or reproductive mycelium. These structures typically extend into the air above the mycelium, hence the name aerial. The spores produced by the aerial mycelium are NOT heat resistant. They are cells which can be spread through the air or in water. When they contact a nutrient rich environment they germinate to produce a new mold. The mycelium growing into the growth surface is specialized for nutrient adsorption and is called the vegetative mycellium.

Viral diseases

Mosquito: encephalitis

Fungal Pathogens

Most fungal pathogens are facultative parasites. They can exist free in the environment growing on some decaying organic matter, or they can enter a host organism, and as a parasite, use host molecules as food. Many pathogens are also dimorphic. The transition from the environment to a host triggers a change in morphology. Some fungi grow like molds in the environment, but switch to yeast-like growth in the host. Others change from yeast-like to mold-like growth when they enter a host. The host environment is a change in both the available nutrients and temperature for the fungi.

Fungal Diseases (Mycoses)

Mycoses are diseases caused by the active growth of fungi in a host organism. (In contrast to mycotoxicosis, a disease caused by eating a fungal toxin). About 50 different fungi are pathogenic for humans. There are two types of mycoses; those that affect the mouth and skin (superficial) and those of internal organs (systemic).

Plasmodium Survival Adaptations

Plasmodium has developed several strategies to enhance its survival in the hostile environment of the host organism. Most of these adaptations help the parasite evade the host's immune system. Although the adaptations described are for plasmodium, they also apply to many other parasites. 1. Plasmodium spends only a few hours in the blood of the human host. The rest of the time (months or years) it is present INSIDE host cells (RBC or liver). This enables the plasmodium to evade our immune system which is very adept at finding and destroying parasites in our body tissues, but OUTSIDE of cells. Many other pathogens (Mycobacterium) use this same strategy. 2. Like Trypanosomes, Plasmodium also rapidly alters surface antigens which allow the immune system to recognize it. 3. Plasmodium, and many other parasites, exhibit an extremely high reproductive capacity when present in the host. This excessive reproductive capacity ensures that some progeny will survive if attacks by the immune system are successful in destroying others.

PROTOZOA:

Protozoa are usually unicellular (though some are colonial), often motile heterotrophs. They are distributed primarily in aquatic environments, but are also found in soil. Some parasitic protozoans exist only in the body of other organisms, particularly the intestinal tract. Protozoans often have the ability to form cysts, a protective covering which helps the organism survive in a harsh environment (when nutrients may be lacking or the temperature unfavorable). This cyst is utilized by many ingested pathogenic protozoans to pass through the acidic stomach environment unharmed.

Eucaryotic Microorganisms:

Protozoa, Algae, Fungi and Helminthic worms.

Schistosoma (fluke)

Schistosomiasis, an infection of the circulatory system characterized by abdominal pain, fever, allergic reactions, inflamation of urinary bladder, neurological destruction and spleen and liver enlargement. Life Cycle: The last larval form to develop in a snail exits the snail and swims in a fresh-water environment until it contacts the body of a human host. This larvae penetrates the skin, enters the blood and moves to the veins in the liver. The worm matures and reproduces in these veins. (There are separate sexes in this particular fluke, but the felmale resides in a body fold of the male.) Sexual reproduction here make humans the definitive host for this parasite. Eggs laid in bloodstream of humans move to the intestine. The eggs are excreted with the feces. If the feces come into contact with fresh water inhabited by a suitable specie of snail, the eggs can hatch to a free-swimming larval form which will penetrate the snail. The fluke goes through several larval stages and reproduces asexually in the snail (the intermediate host) before it forms the last larval stage which will reinfect a human host.

Taenia solium

Taeniasis solium (pork tapeworm), usually asymptomatic, ingested as uncooked pork (bladderworm stage in muscle) -> small intestive -> feces (eggs) -> pig]

Plasmodium

There are several species of Plasmodium which cause the disease malaria. The disease is characterized by recurrent severe chills followed by a high fever, sweating, nausea, vomiting, headache and muscle pain. These symptome reoccur at regular intervals which last from weeks to months. As the disease progresses, brain function is affected, a potentially life-threatening complication. The disease is spread to humans through the bite of mosquitos of the genus Anopheles. (Members of this genus are present in the San Joaquin Valley.) The plasmodium is present in the salivary glands of the mosquito in a form referred to as a sporozoite. When the mosquito draws a blood meal from a human, it injects some saliva containing the sporozoite into the bite. (Anticoagulants are present in the saliva to prevent blood coagulation.) The sporozoites travel through the blood of the host and enter liver cells. Here the Plasmodium reproduces asexually (called schizogony) to produce numerous merozoites. The merozoites are released into the blood by the destruction of the liver cells. Within a few hours the merozoites enter red blood cells (RBC). Here they again reproduce asexually producing numerous merozoites. All of the plasmodium reproduction which occurs in the human is asexual. Humans are therefore the intermediate host for plasmodium (they do NOT reproduce sexually in humans). The RBCs eventually lyse, releasing merozoites into the blood stream, along with all the excretory byproducts of plasmodium metabolism which have accumulated in the RBC. These excretory products are believed to be the cause of the characteristic chills and fever which accompany the disease (we will discuss fever in chapter 16). The merozoites rapidly infect new RBCs in which they will reproduce. In this manner (merozoites infecting, destroying and reinfecting RBCs) the disease can reoccur over a period of years. Occasionally a merozoite which infects a RBC will NOT reproduce, but instead develops into either a specialized "male" or "female" plasmodium called a gametocyte. If a mosquito ingests RBCs containing gametocytes, these plasmodium forms will fuse (fertilization of sexual reproduction) in the intestine of the mosquito. This sexual reproduction is termed sporogony. Hence, the mosquito is the definitive host for plasmodium; sexual reproduction occurs here. The resulting zygote develops into sporozoites which migrate to the salivary glands, waiting to be injected into a human when bitten by the mosquito. Sickle cell hemoglobin provides resistance (protozoans can not grow in such RBC).

Mastigophora (flagellates)

These protozoa have flagella, whip like structures which propel the organism through the environment. Some flagella run the length of the organism and are covered by a portion of the cell membrane which forms a fin used for swimming. This fin-like structure is referred to as an undulating membrane. Examples: Giardia and Trypanosoma

Sporozoa (apicomplexans)

These protozoa have no locomotor organelles in their mature form, though gametes or immature cells may be motile. All members are obligate parasites, they exist only inside some host organism. These organisms are able to differentiate, form different specialized cell types throughout their life cycle which tends to be complex, often involving more than one host. Example: Plasmodium

Trypanosoma brucei

This organism causes african sleeping sickness. Symptoms associated with this disease are anemia, fever, conjunctivitis (eyelid inflamation), headache, vomiting and paralysis. This paralysis affects the CNS, producing a coma, "sleeping", in the latter stages of the disease and eventually results in death. All of these symptoms are caused by the spreading of the organism throughout an infected individuals body which may take many months. The disease is spread by the Tsetse fly which infects human hosts via a bite (infection begins in the bloodstream). The Tsetse fly acts as the vector for this disease, it carries the protozoan. This fly is itself also a host to the organism, although the protozoan does not reproduce sexually in the fly. A organism which is the host to the nonreproductive (or asexually reproductive) form of a parasite is referred to as an intermediate host. Therefore the fly is the intermediate host for the trypanosome. An organism which is a host to the sexually reproductive form of the organism is referred to as the definitive host. Humans are the definitive host for this parasite. The trypanosome causes direct damage to the host's tissues as it migrates through the body. The host's immune system is normally able to recognize and neutralize most pathogens, especially those, like Trypanosoma, which remain in the host for a prolonged period of time. The Trypanosoma is able to evade the host's immune system by altering molecules (antigens) located on the surface of the organism. These antigens are utilized as targets by the immune system. By constantly varying or changing these antigens, the trypanosome is able to remain invisible to the host immune system. Many other parasites also utilize this strategy of antigen variation for immune system evasion.

Giardia lamblia

This organism causes giardiasis, an intestinal infection accompanied by diarrhea and cramps, although most infected individuals are asymptomatic. The organism is orally transmitted in fecally contaminated food or water. Ingested as a cyst, the vegetative cell attaches to the intestinal wall. The surface of the cell is modified to act as a sucker. After reproducing cysts are shed in the feces. This organism does not usually cause severly harm the host. It may contribute to host malnutrition in individuals infected with multiple parasites by eating nutrients from the host's diet.

Parasitic diseases

Tsetse fly: african sleeping sickness

Yeast

Yeast can be characterized as single celled fungi. They reproduce sexually through a process which involves spore formation or asexually by a process termed budding. In budding a "mother" cell divides asymetrically by mitosis to produce a smaller, attached "daughter" cell which will separate from the mother. Both cells produced by budding are genetically identical. If the bud does not separate from the parent cell these two cells are called a pseudomycelium.

Yeast Reproduction

asexual & sexual possible in most fungi (in some, only asexual has been observed). Asexual is by mitosis of a haploid individual. Sexual often involves fusion of haploid gametes (generated by a haploid organism) without fusion of their nuclei (plasmogamy) leading to production of a dikaryotic cell. Only latter will the nuclei fuse (karyogamy) to produce a diploid zygote which then produces haploid spores (specialized reproductive cells) by mitosis. The spores can germinate to form a haploid organism.

Entamoeba histolytica

causes amoebiasis or amebic dysentery. This disease is an intestinal infection characterized by acute diarrhea, abdominal cramps, weight loss and fatigue. The organism is orally transmitted in contaminated water or food. It's presence indicates fecal contamination. An encysted form of the amoeba is injested. The cyst passes unharmed through the stomach. Upon reaching the intestines the vegetative (growing) form of the organism emerges from the cyst and begins to feed on intestinal bacteria. After reproducing the the organism encysts and the cysts are shed in the feces. The organism is also able to directly damage the host's intestinal lining, producing characteristic flask-shaped ulcers. This is a major disease, 10% of the world's population is infected. Many of these individuals are asymptomatic carriers of the organism.

Taenia saginata

causes the disease beef tapeworm. Disease symptoms are abdominal pain, headache, loss of appetite and nausea. Most of the time infected individuals are asymptomatic (have no symptoms). The parasite is transmitted orally in undercooked or raw beef. This parasite can contribute to host malnutrition by feeding on host food. Life Cycle: Humans become infected when they eat an encysted larval form of the tapeworm present in the muscle of beef. The ingested cyst passes through the stomach. In the intestine the tapeworm "hatches" from it's cyst and attaches to the intestinal wall by it's scolex. The worm feeds on host food, grows longer by adding more proglottids to it's body and reproduces sexually in the human intestine (the definitive host). Mature proglottids which are filled with eggs eventually detach from the body of the worm and are excreted with the feces of the host. Cattle become infected by eating vegitation contaminated with the feces. (Human feces is used as fertilizer in many parts of the world.) The egg hatches in the cow (the intermediate host) to produce a larvae which migrates to muscle and encysts; waiting to be eaten by a human.

Trichinella spiralis

causes the diseasem Trichinosis; an intestinal and muscular infection. This disease causes diarrhea, muscular pain, nervous disorders and eosinophilia; high eosinophils (a type of immune system cell described in chapter 16) in blood. The parasite is ingested as a larvae which is covered by a protective shell called a cyst. The encysted nematode is typically found in raw or undercooked pork. [The pig became infected with the parasite by eating food contaminated with cysts of the worm. The worm "hatches" from the cyst after passing through the stomach of the pig. It attaches to the intestinal mucosa of the digestive tract and eats the contents of the hosts intestine. Reproduction occurs in the intestine. The larvae produced migrate into host's muscle where they encyst; waiting to be ingested by another host.] After being ingested by a human, the parasite develops and reproduces just as it does in the pig. Larvae migrate into muscle tissue and encyst. These parasites damage the host by depriving it of nutrients and by diractly damaging primarily muscular tissue.

ARTHROPODS (insects)

ectoparasites which are vectors for transmitting primarily bacterial and viral diseases.

Trichomonas

genitourinary trichomoniasis; in males asymptomatic can lead to prostate involvement, in females a discharge and irritation, can lead to sterility; venereal disease (sexual transmission) also transmitted to new born.

Balantidium

injested as cyst; causes dysentery (feed on colon bacteria)

Enterobius vermicularis; Pinworm

itching in perianal area; ingestion of ova (eggs) -> small intestine (larvae) -> large intestine (maturation & reproduction) -> eggs laid in perianal region.]

Ciliophora (ciliates)

move through the use of cilia, numerous short flagella. These cilia are not only used for locomoyion. They are often distributed around specific locations on the organism surface which act as mouths (oral groove). Here they generate water currents which drag food particles such as bacteria into the organism's oral goove or cytostome. Example: Paramecium

Sarcodina (amoebas)

move using pseudopodia (false feet). These are regions of the cell membrane which are actively extended into the environment in the direction of motion. The cytoplasm of the cell flows into these extensions which draws the organism forward. Pseudopods are also used to engulf food (phagocytosis). The food becomes enclosed in a vacuole. Example: Entamoeba