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Fungi, Algae, Protozoa, and Parasites


I. FUNGI (Mycology) Diverse group of heterotrophs. Many are ecologically important saprophytes (consume dead and decaying matter) Others are parasites. Most are multicellular, but yeasts are unicellular. Most are aerobes or facultative anaerobes. Cell walls are made up of chitin (polysaccharide). Over 100,000 fungal species identified. Only about 100 are human or animal pathogens. Most human fungal infections are nosocomial and/or occur in immunocompromised individuals (opportunistic infections). Fungal diseases in plants cause over 1 billion dollars/year in losses.


CHARACTERISTICS OF FUNGI 1. Yeasts Unicellular fungi, nonfilamentous, typically oval or spherical cells. Reproduce by mitosis: Fission yeasts: Divide evenly to produce two new cells (Schizosaccharomyces). Budding yeasts: Divide unevenly by budding (Saccharomyces). Budding yeasts can form pseudohypha, a short chain of undetached cells. Candida albicans invade tissues through pseudohyphae. Yeasts are facultative anaerobes, which allows them to grow in a variety of environments. When oxygen is available, they carry out aerobic respiration. When oxygen is not available, they ferment carbohydrates to produce ethanol and carbon dioxide.


CHARACTERISTICS OF FUNGI (Continued) 2. Molds and Fleshy Fungi Multicellular, filamentous fungi. Identified by physical appearance, colony characteristics, and reproductive spores. Thallus: Body of a mold or fleshy fungus. Consists of many hyphae. Hyphae (Sing: Hypha): Long filaments of cells joined together. Septate hyphae: Cells are divided by cross-walls (septa). Coenocytic (Aseptate) hyphae: Long, continuous cells that are not divided by septa. Hyphae grow by elongating at the tips. Each part of a hypha is capable of growth. Vegetative Hypha: Portion that obtains nutrients. Reproductive or Aerial Hypha: Portion connected with reproduction. Mycelium: Large, visible, filamentous mass made up of many hyphae.

Characteristics of Fungal Hyphae: Septate versus Coenocytic: 

Characteristics of Fungal Hyphae: Septate versus Coenocytic

Mycelium: Large, Visible Mass of Hyphae: 

Mycelium: Large, Visible Mass of Hyphae


CHARACTERISTICS OF FUNGI (Continued) Dimorphic Fungi Can exist as both multicellular fungi (molds) and yeasts. Many pathogenic species. Mold form produces aerial and vegetative hyphae. Yeast form reproduces by budding. Dimorphism in pathogenic fungi typically depends on temperature: At 37oC: Yeast form. At 25oC: Mold form. Dimorphism in nonpathogenic fungi may depend on other factors: Carbon dioxide concentration.


LIFE CYCLE OF FUNGI Filamentous fungi can reproduce asexually by fragmentation of their hyphae. Fungal spores are formed from aerial hyphae and are used for both sexual and asexual reproduction. 1. Asexual spores: Formed by the aerial hyphae of one organism. New organisms are identical to parent. Conidiospore: Unicellular or multicellular spore that is not enclosed in a sac. Chlamydospore: Thick-walled spore formed within a hyphal segment. Sporangiospore: Asexual spore formed within a sac (sporangium). 2. Sexual spores: Formed by the fusion of nuclei from two opposite mating strains of the same species. New organisms are different from both parents.


IMPORTANT DIVISIONS OF FUNGI 1. Deuteromycota Not known to produce sexual spores. Reproduce asexually. Catch-all category for unclassified fungi: Pneumocystis carinii: Causes pneumonia in AIDS patients. Leading cause of death in AIDS patients. Originally classified as a protozoan. Candida albicans: Causes yeast infections of vagina in women. Opportunistic infections of mucous membranes in AIDS patients.

Opportunistic Infection by Candida albicans in an AIDS Patient : 

Opportunistic Infection by Candida albicans in an AIDS Patient Source: Atlas of Clinical Oral Pathology, 1999


IMPORTANT DIVISIONS OF FUNGI 2. Zygomycota (Conjugation Fungi) Also known as bread molds. Saprophytic molds with coenocytic hyphae (lack septa). Asexual Reproduction: Used most of the time. Sporangiospore: Asexual spore enclosed within a sporangium or sac at the end on an aerial hypha. Sexual Reproduction: Occurs through conjugation, the joining of hypha of two different strains (plus and minus). Zygospores: Sexual spores which are enclosed in a thick, resistant wall. Generally not pathogens. Rhizopus nigricans: Common black bread mold. May cause opportunistic infections in diabetes patients

Life Cycle of a Zygomycete: Black Bread Mold (Rhizopus) Reproduces Asexually and Sexually: 

Life Cycle of a Zygomycete: Black Bread Mold (Rhizopus) Reproduces Asexually and Sexually

Reproductive Structures of Zygomycete (Rhizopus) Sporangia (asexual) and Zygospore (sexual): 

Reproductive Structures of Zygomycete (Rhizopus) Sporangia (asexual) and Zygospore (sexual)


IMPORTANT DIVISIONS OF FUNGI 3. Ascomycota (Sac Fungi) Molds with septate hyphae and some yeasts. Asexual Reproduction: Conidiospores not enclosed in a sac. Become airborne easily. Form chains (broom-like structures). Sexual Reproduction: Ascospores enclosed in a sac-like structure (ascus). Include common antibiotic producing fungi and yeasts, and several human pathogens. Penicillium notatum (Produces penicillin) Saccharomyces (Brewer’s yeast) Trychophyton (Athlete’s foot) Aspergillus (Carcinogenic aflatoxin in peanuts), Blastomyces (Respiratory infections) Histoplasma capsulatum (Respiratory and systemic infections)

Life Cycle of Eupenicillium (Ascomycete) Reproduces Asexually and Sexually: 

Life Cycle of Eupenicillium (Ascomycete) Reproduces Asexually and Sexually


Severe nail infection with Trichophyton rubrum in a 37-year-old male AIDS patient. Source: Intern. J. Dermatol. 31(1992): 453.


Disseminated Histoplasma capsulatum, skin infection. Source: Microbiology Perspectives, 1999.


IMPORTANT DIVISIONS OF FUNGI 4. Basidiomycota (Club Fungi) Have septate hyphae. Include mushrooms, toadstools, rusts, and smuts. Sexual Reproduction: Produce basidiospores: Spores formed externally on a club shaped sexual structure or base called basidium. Asexual Reproduction: Through hyphae. Examples: Cryptococcus: Causes opportunistic respiratory and CNS infections in AIDS patients. Amanita: Mushroom produces lethal toxins to humans. Claviceps purpurea: Produces ergot toxin in wheat and rye.

Life Cycle of a Basidiomycete Mushrooms are Produced Sexually: 

Life Cycle of a Basidiomycete Mushrooms are Produced Sexually


NUTRITIONAL ADAPTATIONS OF FUNGI Fungi absorb their food, rather than ingesting it. Fungi grow better at a pH of 5, which is too acidic for most bacteria. Almost all molds are aerobic. Most yeasts are facultative anaerobes. Fungi are more resistant to high osmotic pressure than bacteria. Fungi can grow on substances with very low moisture. Fungi require less nitrogen than bacteria to grow. Fungi can break down complex carbohydrates (wood, paper), that most bacteria cannot.


FUNGAL DISEASES Mycosis: Any fungal disease. Tend to be chronic because fungi grow slowly. Mycoses are classified into the following categories: I. Systemic mycoses: Fungal infections deep within the body. Can affect a number if tissues and organs. Usually caused by fungi that live in the soil and are inhaled. Not contagious. Examples: Histoplasmosis (Histoplasma capsulatum): Initial infection in lungs. Later spreads through blood to most organs. Coccidiomycosis (Coccidioides immites): Resembles tuberculosis.

Systemic Mycosis: Histoplasmosis: 

Systemic Mycosis: Histoplasmosis Disseminated Histoplasma capsulatum, lung infection. Source: Microbiology Perspectives, 1999.


FUNGAL DISEASES (Continued) II. Cutaneous mycoses: Fungal infections of the skin, hair, and nails. Secrete keratinase, an enzyme that degrades keratin. Infection is transmitted by direct contact or contact with infected hair (hair salon) or cells (nail files, shower floors). Examples: Ringworm (Tinea capitis and T. corporis) Athlete’s foot (Tinea pedis) Jock itch (Tinea cruris)

Cutaneous Mycosis: 

Cutaneous Mycosis Ringworm skin infection: Tinea corporis Source: Microbiology Perspectives, 1999

Cutaneous Mycosis: 

Cutaneous Mycosis Candida albicans infection of the nails. Source: Microbiology Perspectives, 1999.


FUNGAL DISEASES (Continued) III. Subcutaneous mycoses: Fungal infections beneath the skin. Caused by saprophytic fungi that live in soil or on vegetation. Infection occurs by implantation of spores or mycelial fragments into a skin wound. Can spread to lymph vessels. IV. Superficial mycoses: Infections of hair shafts and superficial epidermal cells. Prevalent in tropical climates.


FUNGAL DISEASES (Continued) Opportunistic mycoses: Caused by organisms that are generally harmless unless individual has weakened defenses: AIDS and cancer patients Individuals treated with broad spectrum antibiotics Very old or very young individuals (newborns). Examples: Aspergillosis: Inhalation of Aspergillus spores. Yeast Infections or Candidiasis: Caused mainly by Candida albicans. Part of normal mouth, esophagus, and vaginal flora.


ECONOMIC IMPORTANCE OF FUNGI 25-50% of harvested fruits and vegetables are damaged by fungi. Fungal infections of plants are commonly called rots, rusts, blights, wilts, and smuts. Phytophthora infestans: Caused great potato famine in mid-1800s. Over 1 million people died from starvation in Ireland. Many immigrated to the U.S. Beneficial fungi: Candida oleophila: Prevents fungal growth on harvested fruits. Saccharomyces cerevisiae: Used to make bread and wine. Genetically engineered yeast strains are used to make proteins (Hepatitis B vaccine). Taxomyces: Produces anticancer drug taxol. Trichoderma: Produces cellulase. Used to make fruit juice.


II. ALGAE Simple eukaryotic photosynthetic autotrophs. Unicellular or multicellular. Kingdom Protista. Most are found in the ocean or other bodies of water. Need water for support, reproduction, and nutrition. Absorb nutrients from the water over entire surface. Reproduction: All reproduce asexually. Some can also reproduce sexually. Most are not pathogens. A few produce toxins that are harmful to humans.


II. ALGAE Vegetative Structures of multicellular algae: Thallus: Body. Lacks conductive tissue. Holdfasts: Anchor alga to rock. Stipes: Hollow, stem-like structures. Does not support weight. Blades: Leaf-like structures. Pneumatocyst: Floating, gas-filled bladder.

Comparison of Algae and Plant Structure: 

Comparison of Algae and Plant Structure


DIVISIONS OF ALGAE Green algae: May be unicellular or multicellular. Have cellulose cell walls, contain chlorophyll a and b, and store starch like plants. Most are microscopic. Live close to water surface. Believed to be the ancestors of terrestrial plants. Brown Algae or Kelp: Macroscopic (up to 50 m long). Most are found in coastal waters, at intermediate depths. Rapid growth. Can be harvested regularly. Red Algae: Live at greater ocean depths than other algae. Red pigments allow them to absorb blue light that penetrates deepest into ocean. Agar is extracted from many red algae. Some produce lethal toxins.

Seaweed is a Multicellular Brown Alga (Laminaria): 

Seaweed is a Multicellular Brown Alga (Laminaria)


DIVISIONS OF ALGAE (Continued) Diatoms: Unicellular or filamentous algae with complex cell walls with silica or calcium. Two parts of cell wall fit together like Petri dish. Distinctive patterns are used for identification. Store energy in form of oil. Some diatoms can cause neurological disease (memory loss and diarrhea) in people who eat mussels, due to domoic acid intoxication. Fossil deposits of diatoms (diatomaceous earth) are used as filtering agents and abrasives in several industries.


Dinoflagellates (Plankton): Unicellular free-floating algae. Rigid structure due to cellulose in plasma membrane. Some dinoflagellates produce neurotoxins, which kill fish, marine mammals, and humans. Paralytic shellfish poisoning: Consumption of clams and mussels that have eaten dinoflagellates (Gonyaulax) that produce neurotoxin. Red Tide: Caused by large concentrations of (Gonyaulax). Euglenoids: Unicellular, flagellated algae. Semi-rigid plasma membrane (pellicle). Most have anterior red eye spot. Frequently studied with protozoa, because lack a cell wall.

Euglenoids are Flagellated, Unicellular Algae: 

Euglenoids are Flagellated, Unicellular Algae


Ecological Importance of Algae Important part of the food chain in aquatic ecosystems because they fix carbon dioxide into organic molecules that can be used by heterotrophs. 80% of the earth’s oxygen is believed to be produced by planktonic algae. Algal blooms are indicators of water pollution. Grow rapidly in water with high concentrations of organic material (sewage or industrial waste). Petroleum and natural gas reserves were formed primarily from diatoms and plankton. Many unicellular algae are symbionts in animals.


III. LICHENS Combination of a green alga (or cyanobacterium) and a fungus. Mutualistic relationship in which each partner benefits. Alga: Provides nutrients by photosynthesis to fungus. Fungus: Provides attachment and protection from desiccation. 20,000 species of lichens occupy unique habitats, in which either fungi or algae could not survive alone: rocks, cement, rooftops, trees, and newly exposed soil. Grow very slowly, secreting acids that break down rocks. Accumulate nutrients needed for plant growth. Sensitive to air pollution. Major food source for tundra herbivores (caribou and reindeer).

Lichens: Combinations of Fungi and Green Algae (or Cyanobacterium): 

Lichens: Combinations of Fungi and Green Algae (or Cyanobacterium)


IV. SLIME MOLDS Have both fungal and animal characteristics. Amoeboid stage Produce spores like fungi Eukaryotic, classified as protists. Cellular and plasmodial (acellular) slime molds. Life Cycle of Cellular Slime Molds: Amoeba stage: Germinate from a spore. Slug stage: Many amoebas aggregate and sheath forms. Migration. Fruiting body: Releases spores which germinate into amoebas. Plasmodial (Acellular) Slime Molds Mass of protoplasm with many nuclei (plasmodium). Capable of sexual reproduction.

Life Cycle of a Cellular Slime Mold: 

Life Cycle of a Cellular Slime Mold


V. PROTOZOA Unicellular, chemoheterotrophic, eukaryotic organisms of kingdom Protista (3-2000 mm). Protozoan means “first animal”. 20,000 species, only a few are pathogens. Most are free-living organisms that inhabit water and soil. Some live in association with other organisms as parasites or symbionts. Reproduce asexually by fission, budding, or schizogony. Some exhibit sexual reproduction (e.g.: Paramecium). Trophozoite: Vegetative stage which feeds upon bacteria and particulate nutrients. Cyst: Some protozoa produce a protective capsule under adverse conditions (toxins, scarce water, food, or oxygen).


V. PROTOZOA (Continued) Nutrition Most are heterotrophic aerobes. Intestinal protozoa can grow anaerobically. Some ingest whole algae, yeast, bacteria, or smaller protozoans. Others live on dead and decaying matter. Parasitic protozoa break down and absorb nutrients from their hosts. Some transport food across the membrane. Others have a protective covering (pellicle) and required specialized structures to take in food. Ciliates take in food through a cytostome. Digestion takes place in vacuoles. Waste may be eliminated through plasma membrane or an anal pore.


Medically Important Protozoa 1. Amoeboflagellates (Phylum Sarcomastigophora) Move using pseudopods (false feet) or flagella. A. Amoebas (Subphylum Sarcodina) Move by extending blunt, lobelike projections (pseudopods). Amoebas engulf food with pseudopods and phagocytize it. Several species cause amoebic dysenteries of varying degrees of severity. Entamoeba hystolytica: Feeds on red blood cells. Produces dysentery and extraintestinal cysts. Dientamoeba fragilis: Found in 4% of humans. Usually commensal. Can cause chronic, mild diarrhea. Other diseases include: Meningoencephalitis: Caused by Naegleria fowleri. Penetrate nasal mucosa of swimmers in warm waters. Mortality rate almost 100%. Keratitis: Caused by Acanthamoeba. Can cause blindness. Associated with use of contact lenses.


B. Flagellates (Subphylum Mastigophora) Move by one or more whiplike flagella. Some parasitic flagellates have up to eight flagella. Most are spindle shaped with flagella projecting from anterior end. Outer membrane is a tough pellicle. Food is ingested through an oral groove or cytosotome. Important pathogens: Trichomonas vaginalis: Causes genital and urinary infections. Has undulating membrane. Lacks a cyst stage. Transmitted sexually or by fomites. Giardia lamblia: Causes a persistent intestinal infection (giardiasis) with diarrhea, nausea, flatulence, and cramps. In U.S. most common cause of waterborne diarrhea. About 7% of U.S. population are healthy carriers. Trypanosoma brucei gambiense: Hemoflagellate (blood parasite). Causes African sleeping sickness. Trypanosoma cruzi: Hemoflagellate that causes Chaga’s disease, a cardiovascular disease common in Texas and Latin America.


Medically Important Protozoa (Continued) 2. Apicomplexans (Phylum Apicomplexa) Not motile in their mature form. Obligate intracellular parasites. Have specialized organelles at tip (apex) of cells that penetrate host tissues. Complex life cycles. May have more than one host. Definitive host: Harbors sexually reproducing form. Intermediate host: In which asexual reproduction occurs.


Medically Important Protozoa (Continued) 2. Apicomplexans (Phylum Apicomplexa) Important pathogens: Plasmodium vivax and falciparum: Cause malaria in humans (intermediate host). Initially treated with quinine, drug resistance is a major problem today. Major cause of worldwide mortality: Kill 3 million people/year and infect 500 million. Transmitted by Anopheles mosquito (definitive host). DDT was used extensively in 1960s in an attempt to eradicate the mosquito vector. Successful vaccine not available yet.

Life Cycle of Plasmodium spp. the Infectious Agent of Malaria: 

Life Cycle of Plasmodium spp. the Infectious Agent of Malaria


Medically Important Protozoa (Continued) 2. Apicomplexans (Phylum Apicomplexa) Important pathogens: Toxoplasma gondii: Causes toxoplasmosis in humans. Causes blindness and lymphatic infections in adults. Dangerous to pregnant women, causes severe neurological defects in unborn children. Cats are part of life cycle, oocysts excreted in feces. Contact with infected feces or meat are means of transmission. Cryptosporidium: Causes respiratory and gallbladder infections in immunosuppressed individuals. Found in intestines of mammals and water. Major cause of death in AIDS patients. Cyclospora cayetensis: New parasite (1996) caused diarrhea associated with raspberries.


Medically Important Protozoa (Continued) 3. Ciliates (Phylum Ciliophora) Move and obtain food using cilia. Only known human pathogen is Balantidium coli, which causes a severe intestinal infection in pigs and humans. 4. Microsporans (Phylum Mycrospora) Obligate intracellular parasites, lack mitochondria and microtubules. Discovered in 1984 to cause chronic diarrhea and conjunctivitis, mainly in AIDS patients.

Paramecium caudatum is a Ciliated Protozoan Conjugation Between Opposite Mating Strains: 

Paramecium caudatum is a Ciliated Protozoan Conjugation Between Opposite Mating Strains


VI. HELMINTHS (WORMS) Characteristics Eukaryotic, multicellular animals that usually have digestive, circulatory, nervous, excretory, and reproductive systems. Worms with bilateral symmetry, head and tail, and tissue differentiation (endoderm, mesoderm, and ectoderm). Parasitic helminths spend most or all of their lives in host and usually have the following specializations: May lack a digestive system. Absorb nutrients from host’s food, body fluids, or tissues. Have a reduced nervous system. Means of locomotion is reduced or absent. Complex reproductive system. Individuals produce many eggs that can infect another host.


VI. HELMINTHS (Continued) Two main groups (phyla) Platyhelminths (Flatworms) Nematoda (Roundworms) Life Cycle Extremely complex Intermediate hosts harbor larval (developmental) stage. Definitive host harbors adult stage. Sexual reproduction strategies: Dioecious: Male and female reproductive organs are found in separate individuals. Monoecious (Hermaphroditic): One animal has both male and female sex organs. Most hermaphrodites copulate with other animals, a few copulate with themselves.


VI. HELMINTHS (Continued) I. Platyhelminths (Flatworms) Flattened from front to back. Include: 1. Trematodes or Flukes Leaf shaped bodies Ventral and oral suckers for attachment and sucking fluids from host. Some can absorb nutrients through their cuticle. Named for host tissues in which adult lives. Blood Fluke (Schistosoma spp.): Cause schistosomiasis which affects over 400,000 immigrants in U.S. and 200 million people worldwide. Cause damage to blood vessels, liver, and many other organs. Live in waters contaminated with feces, burrow through skin of human and enter the circulatory system, particularly abdominal and pelvic veins.

Free-Living Flatworm Life Cycle of Blood Fluke Planaria (Schistosoma): 

Free-Living Flatworm Life Cycle of Blood Fluke Planaria (Schistosoma)


VI. HELMINTHS (Continued) I. Platyhelminths (Flatworms) 1. Trematodes or Flukes Asian Liver Fluke (Clonorchis sinensis): Infests gallbladder, bile ducts, pancreatic ducts, causes biliary cirrhosis and jaundice. Cannot be transmitted in U.S. because intermediate hosts are not available. Lung Fluke (Paragonius westermani): Lives in bronchioles of humans and other animals. 12 mm long. Infection from eating undercooked crayfish.

Asian Liver Fluke (Clonorchis sinensis): 

Asian Liver Fluke (Clonorchis sinensis) Source:


VI. HELMINTHS (Continued) I. Platyhelminths (Flatworms) 2. Cestodes or Tapeworms Long flat bodies Intestinal parasites Lack a digestive system, absorb food through cuticle. Body Organization: Head or scolex has suckers for attachment. Body is made up of segments called proglottids. Each proglottid has both male and female reproductive organs. Proglottids farthest from head are mature and contain many fertilized eggs.

Cestode (Tapeworm) Body Structure: Scolex and Proglottids: 

Cestode (Tapeworm) Body Structure: Scolex and Proglottids


VI. HELMINTHS (Continued) I. Platyhelminths (Flatworms) Cestodes or Tapeworms (Continued) Parasitic human tapeworms: Beef Tapeworm (Taenia saginata): Human is definitive host. Can reach up to 6 meters in length, scolex is 2 mm long with hundreds of proglottids. Infection occurs by ingestion of contaminated, undercooked beef (“measly beef”). Pork Tapeworm (Taenia solium): Human is definitive host. Infection can occur from eating infected undercooked pork (rare in the U.S.) or from human to human contact. Echinococcus granulosus: Dogs and coyotes are definitive hosts. Humans may become infected by contact with dog feces or saliva.


VI. HELMINTHS (Continued) II. Nematodes (Roundworms) Cylindrical body tapered at each end. Have a complete digestive system: mouth, intestine, and anus. Body is covered by tough cuticle that resists drying and crushing. Most species are dioecious: separate males and females. Males are smaller than females and have one or two spicules on posterior end. Over 90,000 known species. Most are free-living. Only about 50 are human parasites. Life cycle of parasitic nematodes is simpler than that of flatworms. Infections can be caused by eggs or larvae.

Comparison of Body Organization of Flatworms, Roundworms, and Earthworms: 

Comparison of Body Organization of Flatworms, Roundworms, and Earthworms Flatworm Earthworm Roundworm


II. Nematodes (Roundworms) Continued Infectious eggs Pinworm (Enterobius vermicularis): Spends entire life in human host. Adults live in large intestine. Female lays eggs in perianal region which causes itching. Up to 90% of children are infected through contaminated clothes or bedding. Infection usually disappears after a few years. Ascaris (Ascaris lumbricoides): Large nematode, up to 30 cm. Dioecious with sexual dimorphism. Live in small intestines of humans, horses, and pigs. Eggs can survive in soil for long time. Infectious larvae Adult Hookworm (Necator americanus): Live in small intestine of humans, eggs are excreted in feces. Enter host by penetrating skin. Enters bloodstream, travels to lungs, swallowed in sputum. Avoided by wearing shoes. Trichinosis (Trichinella spiralis): Reproduce sexually in small intestine of humans. Obtained from eating undercooked pork. Larvae enter blood vessels and form cysts throughout body. Anisakines (Wriggly worms): Infected fish and squid. Killed by freezing and cooking.

Pinworm (Enterobius vermicularis): 

Pinworm (Enterobius vermicularis) Source:

Pinworm Eggs (Enterobius vermicularis): 

Pinworm Eggs (Enterobius vermicularis) Source:

Ascaris (Ascaris lumbricoides): 

Ascaris (Ascaris lumbricoides) Source:

Head of Ascaris (Ascaris lumbricoides) : 

Head of Ascaris (Ascaris lumbricoides) Notice three lips characteristic of Ascaris Source: www.


VII. Arthropods as Vectors Segmented bodies, hard exoskeleton (chitin), and jointed legs. Largest phylum in animal kingdom, over 1 million species. Several classes of arthropods: Arachnida (8 legs): Spiders, mites, and ticks. Crustacea (4 antennae): Crabs, crayfish. Most are aquatic. Insecta (6 legs): Largest group of living organisms on earth. Include bees, flies, lice, cockroaches, mosquitoes, and fleas. Arthropods that transmit microbial diseases are called vectors. How do arthropod vectors transport microbes? Mechanically: Houseflies and cockroaches. Hosts: Tick vectors of Lyme disease. Mosquito vectors of malaria and encephalitis.

Arachnids are Arthropods with Eight Legs: 

Arachnids are Arthropods with Eight Legs Lyme Disease Vector Spotted Mountain Fever and Tularemia Vector Source: www.

Insects are Arthropods with Six Legs: 

Insects are Arthropods with Six Legs Source: www. Tse-tse Fly: Host Vector of African Sleeping Sickness

Crustaceans are Arthropods with Four Antennae: 

Crustaceans are Arthropods with Four Antennae

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