I. FUNGI (Mycology) u Diverse group of heterotrophs.
u Many are ecologically important saprophytes(consume dead and decaying matter) Chapter 12: u Others are parasites. Fungi, Algae, Protozoa, and u Most are multicellular, but yeasts are unicellular. u Most are aerobes or facultative anaerobes. Parasites u Cell walls are made up of chitin (polysaccharide). u Over 100,000 fungal species identified. Only about 100 are human or animal pathogens.
u Most human fungal infections are nosocomial and/or occur in immunocompromised individuals (opportunistic infections). u Fungal diseases in plants cause over 1 billion dollars/year in losses.
CHARACTERISTICS OFFUNGI (Continued) CHARACTERISTICS OFFUNGI 2. Molds and Fleshy Fungi 1. Yeasts u Multicellular, filamentous fungi. u Unicellular fungi, nonfilamentous, typically oval or u Identified by physical appearance, colony characteristics, spherical cells. Reproduce by mitosis: and reproductive spores. u Fission yeasts: Divide evenly to produce two new cells u Thallus: Body of a mold or fleshy fungus. Consists of many (Schizosaccharomyces). hyphae.
u Budding yeasts: Divide unevenly by budding (Saccharomyces). u Hyphae (Sing: Hypha): Long filaments of cells joined together. Budding yeasts can form pseudohypha, a short chain of u Septate hyphae: Cells are divided by cross-walls (septa). undetached cells. u Coenocytic (Aseptate) hyphae: Long, continuous cells that are not divided by septa. Candida albicans invade tissues through pseudohyphae. Hyphae grow by elongating at the tips. u Yeasts are facultative anaerobes, which allows them to Each part of a hypha is capable of growth. grow in a variety of environments. u Vegetative Hypha: Portion that obtains nutrients. u Reproductive or Aerial Hypha: Portion connected with u When oxygen is available, they carry out aerobic respiration. reproduction. u When oxygen is not available, they ferment carbohydrates to produce u Mycelium: Large, visible, filamentous mass made up of many ethanol and carbon dioxide. hyphae.
Mycelium: Large, Visible Mass of Hyphae Characteristics of Fungal Hyphae: Septate versus Coenocytic
1 LIFECYCLEOFFUNGI CHARACTERISTICS OFFUNGI (Continued) u Filamentous fungi can reproduce asexually by Dimorphic Fungi fragmentation of their hyphae. u Can exist as both multicellular fungi (molds) and yeasts. u Fungal spores are formed from aerial hyphae and are u Many pathogenic species. used for both sexual and asexual reproduction. u Mold form produces aerial and vegetative hyphae. 1. Asexual spores: Formed by the aerial hyphae of one organism. u Yeast form reproduces by budding. New organisms are identical to parent. u Dimorphism in pathogenic fungi typically depends on u Conidiospore: Unicellular or multicellular spore that is not temperature: enclosed in a sac.
u At 37oC: Yeast form. u Chlamydospore: Thick-walled spore formed within a hyphal segment. u At 25oC: Mold form. u Sporangiospore: Asexual spore formed within a sac u Dimorphism in nonpathogenic fungi may depend on other (sporangium). factors: Carbon dioxide concentration. 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 Opportunistic Infection by Candida 1. Deuteromycota albicans in an AIDS Patient u Not known to produce sexual spores. u Reproduce asexually. u Catch-all category for unclassified fungi:
u Pneumocystis carinii: Causes pneumonia in AIDS patients. Leading cause of death in AIDS patients. Originally classified as a protozoan.
u Candida albicans : Causes yeast infections of vagina in women. Opportunistic infections of mucous membranes in AIDS patients. Source: Atlas of Clinical Oral Pathology, 1999
IMPORTANT DIVISIONS OF FUNGI Life Cycle of a Zygomycete : Black Bread Mold (Rhizopus) Reproduces Asexually and Sexually 2. Zygomycota (Conjugation Fungi) u Also known as bread molds. u Saprophytic molds with coenocytic hyphae (lack septa). u Asexual Reproduction: Used most of the time. Sporangiospore: Asexual spore enclosed within a sporangium or sac at the end on an aerial hypha. u 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. u Generally not pathogens. u Rhizopus nigricans: Common black bread mold. May cause opportunistic infections in diabetes patients
2 Reproductive Structures of Zygomycete (Rhizopus) IMPORTANT DIVISIONS OF FUNGI Sporangia (asexual) and Zygospore (sexual) 3. Ascomycota (Sac Fungi) u Molds with septate hyphae and some yeasts.
u Asexual Reproduction: Conidiospores not enclosed in a sac. Become airborne easily. Form chains (broom-like structures).
u Sexual Reproduction: Ascospores enclosed in a sac-like structure (ascus). u Include common antibiotic producing fungi and yeasts, and several human pathogens. u Penicillium notatum (Produces penicillin) u Saccharomyces(Brewer’s yeast) u Trychophyton(Athlete’s foot) u Aspergillus (Carcinogenic aflatoxin in peanuts), u Blastomyces(Respiratory infections) u Histoplasma capsulatum (Respiratory and systemic infections)
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.
IMPORTANTDIVISIONS OFFUNGI 4. Basidiomycota (Club Fungi)
u Have septate hyphae.
u Include mushrooms, toadstools, rusts, and smuts.
u Sexual Reproduction: Produce basidiospores: Spores formed externally on a club shaped sexual structure or base called basidium.
u Asexual Reproduction: Through hyphae. u Examples:
u Cryptococcus: Causes opportunistic respiratory and CNS infections in AIDS patients. Disseminated Histoplasma capsulatum, skin infection. u Amanita: Mushroom produces lethal toxins to humans. Source: Microbiology Perspectives, 1999. u Claviceps purpurea: Produces ergot toxin in wheat and rye.
3 Life Cycle of a Basidiomycete NUTRITIONAL ADAPTATIONS OFFUNGI Mushrooms are Produced Sexually Fungi absorb their food, rather than ingesting it.
u Fungi grow better at a pH of 5, which is too acidic for most bacteria.
u Almost all molds are aerobic. Most yeasts are facultative anaerobes.
u Fungi are more resistant to high osmotic pressure than bacteria. u Fungi can grow on substances with very low moisture.
u Fungi require less nitrogen than bacteria to grow.
u Fungi can break down complex carbohydrates (wood, paper), that most bacteria cannot.
FUNGAL DISEASES Systemic Mycosis: Histoplasmosis 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.
u Usually caused by fungi that live in the soil and are inhaled. Not contagious.
u Examples:
u Histoplasmosis (Histoplasma capsulatum): Initial infection in lungs. Later spreads through blood to most organs. Disseminated Histoplasma capsulatum,lung infection. u Coccidiomycosis (Coccidioides immites): Resembles tuberculosis. Source: Microbiology Perspectives, 1999.
FUNGAL DISEASES (Continued) Cutaneous Mycosis II.Cutaneous mycoses: Fungal infections of the skin, hair, and nails.
u Secrete keratinase, an enzyme that degrades keratin.
u Infection is transmitted by direct contact or contact with infected hair (hair salon) or cells (nail files, shower floors).
u Examples:
u Ringworm(Tinea capitis and T. corporis) u Athlete’s foot(Tinea pedis) u Jock itch(Tinea cruris)
Ringworm skin infection: Tinea corporis Source: Microbiology Perspectives, 1999
4 Cutaneous Mycosis FUNGAL DISEASES (Continued) III. Subcutaneous mycoses: Fungal infections beneath the skin.
u Caused by saprophytic fungi that live in soil or on vegetation. u Infection occurs by implantation of spores or mycelial fragments into a skin wound.
u Can spread to lymph vessels.
IV. Superficial mycoses: Infections of hair shafts and superficial epidermal cells. Prevalent in tropical climates. Candida albicans infection of the nails. Source: Microbiology Perspectives, 1999.
ECONOMIC IMPORTANCE OF FUNGI FUNGAL DISEASES (Continued) u 25-50% of harvested fruits and vegetables are damaged Opportunistic mycoses: Caused by organisms that are by fungi. generally harmless unless individual has weakened u Fungal infections of plants are commonly called rots, defenses: rusts, blights, wilts, and smuts. u AIDS and cancer patients u Phytophthora infestans: Caused great potato famine in mid- u Individuals treated with broad spectrum antibiotics 1800s. Over 1 million people died from starvation in Ireland. u Very old or very young individuals (newborns). Many immigrated to the U.S. u Examples: u Beneficial fungi: u Aspergillosis: Inhalation of Aspergillus spores. u Candida oleophila: Prevents fungal growth on harvested fruits. u Yeast Infections orCandidiasis: Caused mainly by Candida u Saccharomyces cerevisiae: Used to make bread and wine. albicans. Part of normal mouth, esophagus, and vaginal flora. u Genetically engineered yeast strains are used to make proteins (Hepatitis B vaccine). u Taxomyces: Produces anticancer drugtaxol. u Trichoderma: Produces cellulase. Used to make fruit juice.
II. ALGAE II. ALGAE u Simple eucaryotic photosynthetic autotrophs. u Vegetative Structures of multicellular algae: u Unicellular or multicellular. Kingdom Protista. u Thallus: Body. Lacks conductive tissue. u Most are found in the ocean or other bodies of water. u Holdfasts: Anchor alga to rock.
Need water for support, reproduction, and nutrition. u Stipes: Hollow, stem-like structures. Does not support u Absorb nutrients from the water over entire surface. weight. u Reproduction: All reproduce asexually. Some can also u Blades: Leaf-like structures.
reproduce sexually. u Pneumatocyst: Floating, gas-filled bladder. u Most are not pathogens. A few produce toxins that are harmful to humans.
5 Comparison of Algae and Plant Structure DIVISIONS OF ALGAE u 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.
u 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. u 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) DIVISIONS OF ALGAE (Continued)
u Diatoms: Unicellular or filamentous algae with complex cell walls with silica or calcium.
u Two parts of cell wall fit together like Petri dish. Distinctive patterns are used for identification. Store energy in form of oil.
u Some diatoms can cause neurological disease (memory loss and diarrhea) in people who eat mussels, due to domoic acid intoxication.
u Fossil deposits of diatoms (diatomaceous earth) are used as filtering agents and abrasives in several industries.
u Dinoflagellates (Plankton): Unicellular free-floating Euglenoids are Flagellated, Unicellular Algae algae. Rigid structure due to cellulose in plasma membrane. Some dinoflagellates produce neurotoxins, which kill fish, marine mammals, and humans. u Paralytic shellfish poisoning: Consumption of clams and mussels that have eatendinoflagellates(Gonyaulax)that produce neurotoxin. u Red Tide: Caused by large concentrations of (Gonyaulax).
u Euglenoids: Unicellular, flagellated algae. Semi-rigid plasma membrane (pellicle). Most have anterior red eye spot. Frequently studied with protozoa, because lack a cell wall.
6 Ecological Importance of Algae III. LICHENS u Important part of the food chain in aquatic ecosystems u Combination of a green alga (or cyanobacterium) and a because they fix carbon dioxide into organic molecules fungus. that can be used byheterotrophs. u Mutualistic relationship in which each partner benefits.
u 80% of the earth’s oxygen is believed to be produced by u Alga: Provides nutrients by photosynthesis to fungus. u Fungus: Provides attachment and protection from desiccation. planktonic algae. u 20,000 species of lichens occupy unique habitats, in which u Algal blooms are indicators of water pollution. either fungi or algae could not survive alone: rocks, u Grow rapidly in water with high concentrations of organic cement, rooftops, trees, and newly exposed soil. material (sewage or industrial waste). u Grow very slowly, secreting acids that break down rocks. u Petroleum and natural gas reserves were formed u Accumulate nutrients needed for plant growth. primarily from diatoms and plankton. u Sensitive to air pollution. u Many unicellular algae are symbionts in animals. u Major food source for tundra herbivores (caribou and reindeer).
Lichens: Combinations of Fungi and Green IV. SLIME MOLDS Algae (or Cyanobacterium) u Have both fungal and animal characteristics. u Amoeboid stage u Produce spores like fungi
u Eucaryotes, classified as protists. u Cellular and plasmodial (acellular) slime molds.
u Life Cycle of Cellular Slime Molds: u Amoeba stage: Germinate from a spore. u Slug stage: Many amoebas aggregate and sheath forms. Migration. u Fruiting body: Releases spores which germinate into amoebas.
u Plasmodial (Acellular) Slime Molds u Mass of protoplasm with many nuclei (plasmodium). u Capable of sexual reproduction.
Life Cycle of a Cellular Slime Mold V. PROTOZOA u Unicellular, chemoheterotrophic, eucaryotic organisms of kingdom Protista (3-2000 m m). u Protozoanmeans “first animal”. u 20,000 species, only a few are pathogens. u Most are free-living organisms that inhabit water and soil. Some live in association with other organisms as parasites or symbionts. u Reproduce asexually by fission, budding, or schizogony. u Some exhibit sexual reproduction (e.g.: Paramecium). u Trophozoite: Vegetative stage which feeds upon bacteria and particulate nutrients. u Cyst: Some protozoa produce a protective capsule under adverse conditions (toxins, scarce water, food, or oxygen).
7 Medically Important Protozoa V. PROTOZOA (Continued) 1.Amoeboflagellates (Phylum Sarcomastigophora) Nutrition Move using pseudopods (false feet) or flagella. u Most are heterotrophic aerobes. Intestinal protozoa can A. Amoebas (Subphylum Sarcodina) grow anaerobically. u Move by extending blunt, lobelike projections (pseudopods). u Some ingest whole algae, yeast, bacteria, or smaller protozoans. Others live on dead and decaying matter. u Amoebas engulf food with pseudopods and phagocytize it. Parasitic protozoa break down and absorb nutrients from u Several species cause amoebic dysenteries of varying their hosts. degrees of severity. u Entamoeba hystolytica: Feeds on red blood cells. Produces u Some transport food across the membrane. dysentery and extraintestinal cysts. u Others have a protective covering (pellicle) and required u Dientamoeba fragilis: Found in 4% of humans. Usually commensal. Can cause chronic, mild diarrhea. specialized structures to take in food. u Ciliates take in food through a cytostome. u Other diseases include: u Meningoencephalitis: Caused by Naegleria fowleri. Penetrate u Digestion takes place in vacuoles. nasal mucosa of swimmers in warm waters. Mortality rate u Waste may be eliminated through plasma membrane or almost 100%. an anal pore. u Keratitis: Caused by Acanthamoeba. Can cause blindness. Associated with use of contact lenses.
B. Flagellates (Subphylum Mastigophora) u Move by one or more whiplike flagella. Some parasitic Medically Important Protozoa (Continued) flagellates have up to eight flagella. 2. Apicomplexans (Phylum Apicomplexa) u Most are spindle shaped with flagella projecting from u Not motile in their mature form. anterior end. u Obligate intracellular parasites. u Outer membrane is a tough pellicle. Food is ingested through an oral groove or cytosotome. u Have specialized organelles at tip (apex) of cells that u Important pathogens: penetrate host tissues. u Trichomonas vaginalis: Causes genital and urinary infections. Has undulating membrane. Lacks a cyst stage. Transmitted u Complex life cycles. May have more than one host. sexually or by fomites. Definitive host: Harbors sexually reproducing form. u Giardia lamblia: Causes a persistent intestinal infection (giardiasis) with diarrhea, nausea, flatulence, and cramps. In Intermediate host: In which asexual reproduction U.S. most common cause of waterborne diarrhea. About 7% of U.S. population are healthy carriers. occurs. u Trypanosoma brucei gambiense: Hemoflagellate(blood parasite). Causes African sleeping sickness. u Trypanosoma cruzi: Hemoflagellate that causesChaga’s disease, a cardiovascular disease common in Texas and Latin America.
Medically Important Protozoa (Continued) Life Cycle of Plasmodium spp. the 2. Apicomplexans (Phylum Apicomplexa) Infectious Agent of Malaria u Important pathogens: u 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 Anophelesmosquito (definitive host). DDT was used extensively in 1960s in an attempt to eradicate the mosquito vector. Successful vaccine not available yet.
8 Medically Important Protozoa (Continued) Medically Important Protozoa (Continued) 2. Apicomplexans (Phylum Apicomplexa) 3. Ciliates (Phylum Ciliophora) u Important pathogens: u Move and obtain food using cilia.
u Toxoplasma gondii: Causestoxoplasmosis in humans. Causes u Only known human pathogen is Balantidium coli, which blindness and lymphatic infections in adults. Dangerous to causes a severe intestinal infection in pigs and humans. pregnant women, causes severe neurological defects in unborn children. Cats are part of life cycle, oocystsexcreted in feces. 4.Microsporans (Phylum Mycrospora) Contact with infected feces or meat are means of transmission. u Obligate intracellular parasites, lack mitochondria and u Cryptosporidium: Causes respiratory and gallbladder infections in immunosuppressedindividuals. Found in intestines of microtubules. mammals and water. Major cause of death in AIDS patients. u Discovered in 1984 to cause chronic diarrhea and u Cyclospora cayetensis: New parasite (1996) caused diarrhea conjunctivitis, mainly in AIDS patients. associated with raspberries.
Paramecium caudatum is a Ciliated Protozoan VI. HELMINTHS (WORMS) Conjugation Between Opposite Mating Strains Characteristics u Eucaryotic, multicellular animals that usuallyhave digestive, circulatory, nervous, excretory, and reproductive systems. u Worms with bilateral symmetry, head and tail, and tissue differentiation (endoderm, mesoderm, and ectoderm). u Parasitic helminths spend most or all of their lives in host and usually have the following specializations: u May lack a digestive system. Absorb nutrients from host’s food, body fluids, or tissues. u Have a reduced nervous system. u Means of locomotion is reduced or absent. u Complex reproductive system. Individuals produce many eggs that can infect another host.
VI. HELMINTHS (Continued) VI. HELMINTHS (Continued) I.Platyhelminths (Flatworms) Two main groups (phyla) Flattened from front to back. u Platyhelminths (Flatworms) Include: u Nematoda (Roundworms) 1. Trematodes or Flukes Life Cycle u Leaf shaped bodies u Extremely complex u Ventral and oral suckers for attachment and sucking u Intermediate hosts harbor larval (developmental) stage. fluids from host. u Definitive host harbors adult stage. u Some can absorb nutrients through their cuticle. u Sexual reproduction strategies: u Named for host tissues in which adult lives. u Dioecious: Male and female reproductive organs are found in u Blood Fluke (Schistosoma spp.): Cause schistosomiasis which separate individuals. affects over 400,000 immigrants in U.S. and 200 million people worldwide. u Monoecious (Hermaphroditic): One animal has both male and Cause damage to blood vessels, liver, and many other organs. female sex organs. Most hermaphrodites copulate with other Live in waters contaminated with feces, burrow through skin of animals, a few copulate with themselves. human and enter the circulatory system, particularly abdominal and pelvic veins.
9 Free-Living Flatworm Life Cycle of Blood Fluke VI. HELMINTHS (Continued) Planaria (Schistosoma ) I.Platyhelminths (Flatworms) 1.Trematodes or Flukes u Asian Liver Fluke (Clonorchis sinensis): Infests gallbladder, bile ducts, pancreatic ducts, causesbiliary cirrhosis and jaundice. Cannot be transmitted in U.S. because intermediate hosts are not available. u 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) VI. HELMINTHS (Continued) I.Platyhelminths (Flatworms) 2.Cestodes or Tapeworms u Long flat bodies u Intestinal parasites u Lack a digestive system, absorb food through cuticle. Body Organization: u Head or scolexhas suckers for attachment. u Body is made up of segments called proglottids . u Eachproglottid has both male and female reproductive organs. u Proglottids farthest from head are mature and contain many fertilized eggs.
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Cestode (Tapeworm) Body Structure: VI. HELMINTHS (Continued) Scolex and Proglottids I.Platyhelminths (Flatworms) Cestodes or Tapeworms (Continued) u Parasitic human tapeworms: u 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”). u 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. u Echinococcus granulosus: Dogs and coyotes are definitive hosts. Humans may become infected by contact with dog feces or saliva.
10 Comparison of Body Organization of Flatworms, VI. HELMINTHS (Continued) Roundworms, and Earthworms II. Nematodes (Roundworms) u Cylindrical body tapered at each end. u Have a complete digestive system: mouth, intestine, and Flatworm anus. u Body is covered by tough cuticle that resists drying and crushing. u Most species are dioecious: separate males and females. Roundworm u Males are smaller than females and have one or two spicules on posterior end. u Over 90,000 known species. Most are free-living. Only about 50 are human parasites. u Life cycle of parasitic nematodes is simpler than that of flatworms. Earthworm u Infections can be caused by eggs or larvae.
II. Nematodes (Roundworms) Continued Infectious eggs u Pinworm (Enterobius vermicularis): Spends entire life in human Pinworm (Enterobius vermicularis) 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. u 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 u 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. u Trichinosis (Trichinella spiralis): Reproduce sexually in small intestine of humans. Obtained from eating undercooked pork. Larvae enter blood vessels and form cysts throughout body. u Anisakines (Wriggly worms): Infected fish and squid. Killed by freezing and cooking. Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Pinworm Eggs (Enterobius vermicularis) Ascaris (Ascaris lumbricoide s)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
11 Head of Ascaris (Ascaris lumbricoides) VII. Arthropods as Vectors u Segmented bodies, hard exoskeleton (chitin), and jointed legs. u Largest phylum in animal kingdom, over 1 million species. u Several classes of arthropods: u Arachnida (8 legs): Spiders, mites, and ticks.
u Crustacea (4 antennae): Crabs, crayfish. Most are aquatic. u Insecta (6 legs): Largest group of living organisms on earth. Include bees, flies, lice, cockroaches, mosquitoes, and fleas. u Arthropods that transmit microbial diseases are called vectors. u How do arthropod vectors transport microbes? Notice three lips characteristic of Ascaris u Mechanically: Houseflies and cockroaches. Source: www. soton.ac.uk/~djab/ascaris.html u Hosts: Tick vectors of Lyme disease. Mosquito vectors of malaria and encephalitis.
Arachnids are Arthropods with Eight Legs Insects are Arthropods with Six Legs
Tse-tse Fly: Host Vector of African Sleeping Sickness
Lyme Disease Vector Spotted Mountain Fever and Tularemia Vector Source: www. soton.ac.uk/~djab/ascaris.html Source: www. soton.ac.uk/~djab/ascaris.html
Crustaceans are Arthropods with Four Antennae
12