classification and nomenclature of bacteria, viruses, fungi and parasites

Will be useful for MBBS students to learn about basic classification and nomenclature of bacteria, viruses, fungi and parasites

1. Classification of bacteria Dr Amudhan Murugesan PhD Department of Microbiology GTMCH

2. Basis of classification Phenotypic classification Morphological Anatomical Staining Cultural characteristics Nutrition Environmental factors Biochemical reactions Antigenic structure Genotypic classification DNA-DNA hybridization G+C content

3. Morphological classification Bacteria can be classified into six major groups on morphological basis. 1. TRUE BACTERIA Cocci – These are spherical or oval cells. On the basis of arrangement of individual organisms they can be described as Monococci ( Cocci in singles) – Monococcus spp. Diplococci ( Cocci in pairs) – Streptococcus pneumoniae Staphylococci ( Cocci in grape-like clusters) – Staphylococcus aureus Streptococci ( Cocci in chains) – Streptococcus pyogenes Tetrad ( Cocci in group of four) - Micrococcus spp. Sarcina ( Cocci in group of eight)

4. Bacilli – These are rod-shaped bacteria. On the basis of arrangement of organisms, they can be described as Diplobacilli Streptobacilli Palisades Chinese-letter form Coccobacilli Comma-shaped

5. Morphological classification 2. ACTINOMYCETES ( actin - ray, mykes -fungus) Thes e are rigid organisms like true bacteria but they resemble fungi in that they exhibit branching and tend to form filaments. They are termed such because of their resemblance to sun rays when seen in tissue sections.

6. Morphological classification 3. Spirochaetes These are relatively longer, slender, non-branched microorganisms of spiral shape having several coils.

7. Morphological classification 4. Mycoplasmas These bacteria lack in rigid cell wall (cell wall lacking) and are highly pleomorphic and of indefinite shape. They occur in round or oval bodies and in interlacing filaments. 5. Rickettsiae and Chlamydiae These are very small, obligate parasites , and at one time were considered closely related to the viruses. Now, these are regarded as bacteria.

8. Based on Anatomical features Capsule Capsulate – Streptococcus pneumoniae Non-capsulate – Viridans streptococci Flagella Flagellate – Monotrichous Lophotrichous Amphitrichous Peritrichous Aflagellate – Shigella spp . Spore Spore-forming – Bacillus spp . Non-sporing – Escherichia coli

9. Based on Staining reaction GRAM’S STAIN Gram-positive cocci – Staphylococcus aureus Gram-negative cocci – Neisseria gonorrhoeae Gram-positive rods – Clostridium spp. Gram-negative rods – E. coli ACID FAST STAIN Acid-fast bacilli – Mycobacterium tuberculosis Non-acid-fast bacilli – Staphylococcus aureus

10. Based on Cultural characteristics Extra growth factors requirements Fastidious – Hemophilus influenzae Non-fastidious – Escherichia coli Hemolysis on Sheep Blood Agar Alpha-hemolysis – Streptococcus pneumoniae Beta-hemolysis – Streptococcus pyogenes Utilization of carbohydrates Oxidative - Micrococcus Fermentative – Escherichia coli

11. Based on Cultural characteristics Growth rate Rapid growers – Vibrio cholerae Slow growers – Mycobacterium tuberculosis Pigment production Pigment producer – Staphylococcus aureus Pigment non-producer – Escherichia coli

12. Based on Nutrition Autotrophs Heterotrophs

13. Based on environmental factors Temperature Oxygen dependence pH Salt concentration Atmospheric pressure

14. Temperature Psychrophiles (15-20 C) – Pseudomonas fluorescens Mesophiles (20-40 C) – Escherichia coli , Salmonella enterica , Staphylococcus aureus Thermophiles (50-60 C)- Bacillus stearothermophilus Extremely thermophiles (as high as 250 C)

15. Oxygen dependence Aerobe (grow in ambient temperature, which contains 21% O 2 and a small amount of CO 2 , 0.03%) Obligate aerobes – Strictly require O 2 for their growth ( Pseudomonas aeruginosa ) Microaerophilic (grow under reduced O 2 , 5-10% and increased CO 2 , 8-10%)- Campylobacter jejuni , Helicobacter pylori

16. Oxygen dependence Facultative anaerobe (capable of growing either in presence or absence of O 2 )- E. coli Obligate anaerobe – Clostridium spp. Capnophilic (require increased concentration of CO 2 , i.e., 5-10%) – H. influenzae , N. gonorrhoeae Aerotolerant

17. pH Acidophiles ( Lactobacillus acidophilus ) Alkaliphiles ( Vibrio ) Neutralophiles (pH 6-8) Majority of the medically important bacteria grow best at neutral or slightly alkaline reaction (pH 7.2-7.6)

18. Salt concentration Halophiles Non-halophiles

19. Other ways of classification Motile/Non-motile Pathogenic/Non-pathogenic Sensitive/Resistant (to particular antibiotic/ chemicals) Lactose fermenter/Lactose non-fermenter Bergey’s Manual of Determinative Bacteriology Gram-negative eubacteria that have cell walls Gram-positive eubacteria that have cell walls Cell wall-less eubacteria: Mycoplasma Archaeobacteria

20. FUNGI

21. OUTLINE Introduction Characteristics Difference between fungi and bacteria Size of fungi Hyphae Types of hyphae Classification of fungi Lifecycle of fungi Beneficial effects of fungi Harmful effects of fungi

22. INTRODUCTION A member of a large group of eukaryotic organisms. Familiar as mushrooms. These organisms are classified as a kingdom, fungi ,which is separate from plants, animals,protists and bacteria. True biodiversity of kingdom fungi,which has been estimated at 1.5 million to 5 million species,with about 5%of these having been formally classified

23. Fungi have been classified according to their morphology or physiology. One major difference is that fungal cells have cell wall that contain chitin ,unlike the cell wall of plants and some protists,which contain cellulose,and unlike the cell walls of bacteria. Genetic studies revealed that fungi are more closely related to animals than to plants. The study of fungi is known as mycology .

24. CHARACTERISTICS OF FUNGI Fungi are not plants. May be unicellular or multicellular. Most are macroscopic molds or yeasts. Reproduce either by budding or by forming spores. Nonphotosynthatic(heterotrophic) Nonmotile.

25. Most are s aprobes (live on dead organisms) Release digestive enzymes to break down organic material or their host. Store food energy as glycogen. Important decomposers and recyclers of nutrients in the environment. Lack true roots, stems or leaves.

26. Some fungi are internal or external hyphae. Some fungi act like predators. Some are edible, while others are poisonous. Produce both sexual and asexual spores. Grow best in warm,moist environment. A fungicide is a chemical used to kill fungi. Fungi includes puffballs ,yeast, mushrooms, toadstools,rusts,smuts,ringworm,and molds. The antibiotic penicillin is made by the penicillium mold.

27. Puffballs Mushrooms Rust Smut Toadstool Ringworm

28. DIFFERENCE BETWEEN FUNGI AND BACTERIA Characteristics FUNGI BACTERIA CELL TYPE EUKARYOTIC PROKARYOTIC OPTIMUM PH 4-6 6.5-7.5 OPTIMUM TEMPERATURE 25-30(SPAROPHYTES) 32-37◦C(PARASITES) 32-37 ◦C CELL MEMBRANE STEROLS PRESENT STEROLS ABSENT EXCEPT MYCOPLASM LIGHT REQUIREMENT NONE SOME PHOTOSYNTHETIC CARBON SOURCE ORGANIC ORGANIC/INORGANIC CELL WALL COMPONENTS CHITIN,CELLULOSE,OR HEMICELLULOSE PEPTIDOGLYCAN SUSCEPTIBILITY TO ANTIBIOTICS SENSITIVE TO GRISEOFULVIN,RESISTANT TO PENICILLIN SENSITIVE TO PENICILLIN,RESISTANT TO GRISEOFULVIN

29. Size of fungi The sizes of fungi vary greatly depending on the type of fungus. In general most microscopic fungi are 2-10 micrometer in diameter. The average size of fungi are 5-50 micrometers in length. Most giant puffballs grow to be 10-50cm sometime to be 90 cm in diameter. Giant puffball

30. Hyphae “Hyphae is a long, branching filamentous structure of fungus.In most fungi, hyphae are the main mode mode of vegetative growth and are collectively called mycelium.” Tubular shape One continuous cell filled with cytoplasm and nuclei. Multinucleate. Hyphae grows from their tip .

31. Stolon : “Horizontal stem like hyphae that connect groups of hyphae to each other are called stolon.” Rhizoids : “Root like hyphae that anchor the fungus are called rhizoids.”

32. T ypes of hyphae Septate hyphae: “Have walls that separate individual cells.” Nonseptate hyphae: “Are one long continuous cell without walls.”

33. CLASSIFICATION OF FUNGI Depending on cell morphology, fungi can be divided into four classes : Moulds Yeasts Yeast like fungi Dimorphic fungi Depending on sexual spore formation fungi are divided into four classes: Phycomycetes Ascomycetes Basidiomycetes Fungi imperfecti

34. MOULDS “ Mould is a type of fungus that consists of small organisms fount almost everywhere. They can be green,white,blank,orange or purple.” Diameter is 2-10 micrometers. The cell wall contain chitin. Plays important role in nature, breaking down dead leaves, plants and trees. Examples: Aspergillus niger penicillium digitatum

35. YEASTS “Yeast are single-celled microorganisms that are classified along with molds and mushrooms, as a member of the kingdom fungi.” R ound, oval or elongated, unicellular fungi. Reproduce by an asexual process called budding. Examples: Saccharomyces Cerevisiae Cryptococcus Neoformans

36. YEAST LIKE FUNGI Yeast like fungi partly grow as yeast and partly as elongated cells resembling hyphae. The latter forms a pseudomycellium. Example: Candida A lbicans

37. DIMORPHIC FUNGI “Dimorphic fungi are the fungi that can exist in the form of both mold and yeast.” Mold like forms produce vegetative and yeast like forms reproduce by budding. Dimorphism is temperature and CO2 dependent. At 37◦C the fungus grows yeast like and at 25◦C it shows mold like growth. Example:Histoplasma c apsulatum

38. PHYCOMYCETES “Fungi having nonseptate hyphae, forms endogenous asexual spores contained within a sac like structure called sporangia.” Also produce sexual spores known as oospores and zygospores. It is also referred as zygomycetes. Examples:rhizopus,mucor,albugo,pythium M ucor Rhizopus

39. ASCOMYCETES It is the largest phylum of fungi with over 64000 species. Forms sexual spores within a sac and are called ascospores.The sac is called as ascus. It is also known as sac fungi. They form septate hyphae. Includes both yeasts and filamentous fungi. Examples:yeast,aspergillus,penicillium, neurospora Neurospora

40. BASIDIOMYCETES Basidiomycota are typically filamentous fungi composed of hyphae. Reproduce sexually and forms septate hyphae. They are also known as club fungi. Examples:Agaricus,Polyporus,Puccinia, Ustilago, PUCCINIA POLYPORUS USTILAGO

41. FUNGI IMPERFECTI The fungi imperfecti or imperfect fungi also known as D euteromycetes or Hyphomycetes. Consist of group of fungi whose sexual phases have not been identified and they form septate hyphae. Imperfect fungi live in warm, damp places as long as there is a food source. Example:Cercospora,Fusarium,Trichoderma CEPHALOSPORA FUSARIUM TRICHODERMA

42. BENEFICIAL EFFECTS OF FUNGI Decomposition-nutrients and carbon recycling. Can be used to produce drugs,antibiotics,alcohals,acids,food(fermented products, mushrooms) Act as model organisms for biochemical and genetic studies. Vitamin production. Hormone production. Edible fungi. Production of insecticides

43. HARMFUL EFFECTS OF FUNGI Destruction of food,lumber,paper,and cloth. Plant diseases. Animal diseases. Human diseases,including allergies. Toxins produced by poisonous mushrooms and within food(grain, cheese)

44. CLASSIFICATION OF VIRUSES

45. INTRODUCTION:- Initially after viruses were discovered there was no system for classifying viruses. Consequently viruses were named randomly. Most of the vertebrate viruses have been named according to: the associated diseases (poliovirus, rabies) the type of disease caused (murine leukemia virus), the sites in the body affected or from which the virus was first isolated (rhinovirus, adenovirus) the places from where they were first isolated (Sendai virus, Coxsackievirus ) the scientists who discovered them (Epstein-Barr virus), or due to common cultural perceptions e.g. influenza ‘influence’ of bad air or dengue  ‘evil spirit’

46. The actual classification of viruses began in the 1960’s when new viruses were being discovered and studied by electron microscopy. When structure was clarified the need for a new system of classification was felt . Lwoff, Horne, and Tournier suggested a comprehensive scheme for classifying all viruses in 1962. Their proposal used the classical Linnaean hierarchical system of phylum, class, order, family, genus and species. Although the full scheme could not be adopted for viruses

47. According to the classification, viruses are grouped according to  their  properties, not the cells they infect. The main criteria were the type of nucleic acid – DNA or RNA . Four characteristics were to be used for the classification of all viruses: Type of the nucleic acid including size of the genome, strandedness (single or double), linear or circular, positive or negative (sense), segments (number and size), sequence and G+C content etc. Symmetry of the protein shell Presence or absence of a lipid membrane Dimensions or the size of the virion and capsid Other properties include the physicochemical properties including molecular mass, pH, thermal stability, susceptibility to chemicals and physical extremes and to ether and detergents.

48. ICTV classification Naming convention primarily depends on the genome and nucleic acid material of the viruses with the development of nucleic acid sequencing technologies in the 1970s. Naming is performed by the International Committee on the Taxonomy of Viruses (ICTV). A complete catalog of known viruses is maintained by the ICTV at ICTVdb .(Database). The order is as follows; Order – virales Family – viridae Subfamily – virinae Genus –virus Species –virus

49. The Baltimore classification This classifies according to the viral mRNA synthesis. This came from Nobel prize winner David Baltimore . ICTV and Baltimore classifications used together At present both ICTV and Baltimore classification are used together Born: 7 March 1938, Died: 6 September 2025 (age 87 years),

50. Classification of virus On the Basis of Genetic Material Present On the basis of the presence of a number of strands On the Basis of Presence of Envelope Virus Classification by Capsid Structure On the Basis of Shapes of the Viruses Classification of Virus on the Basis of Structure On the Basis of the Type of Host Classification of Virus on the Basis of Mode of Transmission Classification of Virus on the Basis of Replication Properties and Site of Replication Baltimore Classification

51. 1. On the Basis of Genetic Material Present Viruses are small, non-living parasites, which cannot replicate outside of a host cell. A virus consists of genetic information — either DNA or RNA — coated by a protein.  Accordingly, they are classified as DNA viruses and RNA viruses. The nucleic acid may be single or double stranded, circular or linear, segmented or unsegmented

52. DNA viruses As their name implies, DNA viruses use DNA as their genetic material. Some common examples of DNA viruses are parvovirus, papillomavirus , and herpesvirus . DNA viruses can affect both humans and animals and can range from causing benign symptoms to posing very serious health. RNA viruses The virus that possesses RNA as genetic material are called RNA viruses. Rotavirus ,  polio virus , yellow fever virus, dengue virus,  hepatitis C virus ,  measles  virus,  rabies virus , influenza virus and  Ebola virus  are examples of RNA virus. DNA-RNA viruses The RNA tumor viruses called Leukoviruses and Rous’s viruses unusually contain both DNA and RNA as genetic material

53. 2. On the basis of the presence of  a number  of strands Double-stranded DNA It is found in pox viruses, the bacteriophages T2, T4, T6, T3, T7 and Lamda , herpes viruses, adenoviruses etc. Single-stranded DNA It is found in bacteriophages φ, X, 74 bacteriophages . Double-stranded RNA It has been found within viral capsid in the reoviruses of animals and in the wound tumour virus and rice dwarf viruses of plants. Single-stranded RNA It is found in most of the RNA viruses eg : tobacco mosaic virus, influenza virus, poliomyelitis, bacteriophage MS-2, Avian leukemia virus.

54. 3. On the Basis of Presence of Envelope The envelope is a lipid-containing membrane that surrounds some virus particles. It is acquired during viral maturation by a budding process through a cellular membrane Virus encoded glycoproteins are exposed on the surface of the envelope. These projections are called peplomers . Enveloped Virus DNA viruses:  Herpesviruses , Poxviruses, Hepadnaviruses RNA viruses:   Flavivirus , Toga virus, Coronavirus, Hepatitis D, Orthomyxovirus , Paramyxovirus , Rhabdovirus , Bunyavirus , Filovirus , Retroviruses Non-Enveloped Virus DNA viruses-  parvovirus, adenovirus and papovavirus . RNA viruses-   Picornavirus , Hepatitis A virus and Hepatitis E virus.

55. 4. Virus Classification by Capsid Structure Naked icosahedral :  Hepatitis A virus, polioviruses Enveloped icosahedral : Epstein-Barr virus, herpes simplex virus, rubella virus, yellow fever virus, HIV-1 Enveloped helical:  Influenza viruses, mumps virus, measles virus, rabies virus Naked helical : Tobacco mosaic virus Complex with many proteins:  some have combinations of icosahedral and helical capsid structures. Herpesviruses , smallpox virus, hepatitis B virus, T4 bacteriophage .

56. 5. On the Basis of Shapes of the Viruses Most of the animal viruses are roughly spherical with some exceptions. Rabies virus:   Bullet shaped Ebola virus:  Filamentous shaped Poxvirus:  Brick shaped Adenovirus:  Space vehicle shaped

57. 6. Classification of Virus on the Basis of Structure Cubical virus:  They are also known as icosahedral symmetry virus Eg . Reo virus, Picorna virus . Spiral virus:  They are also known as helical symmetry virus Eg . Paramyxovirus , orthomyxovirus . Radial symmetry virus:  eg . Bacteriophage . Complex virus:  eg . Pox virus

58. Helical symmetry There are several viruses found with a helical morphology. These viruses consist of identical protein subunits or protomers which assembled in a helical structure around the genome. This type of protein subunits generally forms a rigid nucleocapsid . Moreover, the helical structure provides flexibility to the filaments. The morphology of this type of viruses can be analyzed by an electron microscope. The helical nucleocapsid is also characterized by length, width, number of promoters per helical turn and pitch of the helix. The most common example of a helical virus is the tobacco mosaic virus. Icosahedral Symmetry An icosahedron structure refers to a type of polyhedron with 20 equilateral triangular faces and 12 vertices. The rigid structure provides protection to the genome. The common examples of viruses reported to have an icosahedral structure are papovavirus , picornavirus , adenovirus, toga virus, etc. Complex Symmetry These groups of viruses do not come under the above-motioned groups. These viruses consist of complex structural components which made it different from the other two groups. A common example of this group of the virus is the pox virus.

59. CLASSIFICATION ON THE BASIS OF MORPHOLOGY (STRUCTURE)

60. 7. On the Basis of the Type of Host The virus can be classified on the basis of the type of host. They are: Animal viruses Plant viruses Bacteriophage

61. Animal Viruses The viruses which infect and live inside the animal cell including man are called animal viruses. Eg ; influenza virus, rabies virus, mumps virus, poliovirus etc. Their genetic material is RNA or DNA. Plant Viruses The viruses that infect plants are called plant viruses. Their genetic material is RNA which remains enclosed in the protein coat. Some plant viruses are tobacco mosaic virus, potato virus, beet yellow virus and turnip yellow virus etc. Bacteriophages Viruses which infect bacterial cells are known as bacteriophage or bacteria eaters. They contain DNA as genetic material. There are many varieties of bacteriophages. Usually, each kind of bacteriophage will attack only one species or only one strain of bacteria.

62. 8. Classification of Virus on the Basis of Mode of Transmission Virus transmitted through respiratory route: Eg , Swine flu, Rhino virus        Virus transmitted through faeco -oral route: Eg . Hepatitis A virus, Polio virus, Rota virus Virus transmitted through sexual contacts: Eg . Retro virus Virus transmitted through blood transfusion: Eg . Hepatitis B virus, HIV Zoonotic virus: Virus transmitted through biting of infected animals; Eg . Rabies virus, Alpha virus,  Flavi virus

63. 9. Classification of Virus on the Basis of Replication Properties and Site of Replication Replication and assembly in cytoplasm of host: All RNA virus replicate and assemble in cytoplasm of host cell except Influenza virus Replication in nucleus and assembly in cytoplasm of host: Influenza virus, Pox virus Replication and assembly in nucleus of host: All DNA viruses replicate and assemble in nucleus of host cell except Pox virus. Virus replication through ds DNA intermediate: All DNA virus, Retro virus and some tumor causing RNA virus replicates through ds DNA as intermediates. Virus replication through ss RNA intermediate : All RNA virus except Reo virus and tumor causing RNA viruses.

64. 10 .Baltimore Classification The most commonly used system of virus classification was developed by Nobel Prize-winning biologist David Baltimore in the early 1970s. In addition to the differences in morphology and genetics mentioned above, the Baltimore classification scheme groups viruses according to how the mRNA is produced during the replicative cycle of the virus.

65. Group I  viruses contain double-stranded DNA ( dsDNA ) as their genome. Their mRNA is produced by transcription in much the same way as with cellular DNA. Group II  viruses have single-stranded DNA ( ssDNA ) as their genome. They convert their single-stranded genomes into a dsDNA intermediate before transcription to mRNA can occur. Group III  viruses use dsRNA as their genome. The strands separate, and one of them is used as a template for the generation of mRNA using the RNA-dependent RNA polymerase encoded by the virus.

66. Group IV  This group viruses have ssRNA as their genome with a positive polarity. Positive polarity means that the genomic RNA can serve directly as mRNA. Intermediates of dsRNA , called replicative intermediates, are made in the process of copying the genomic RNA. Multiple, full-length RNA strands of negative polarity (complementary to the positive-stranded genomic RNA) are formed from these intermediates, which may then serve as templates for the production of RNA with positive polarity, including both full-length genomic RNA and shorter viral mRNAs.

67. Group V  viruses contain ssRNA genomes with a negative polarity, meaning that their sequence is complementary to the mRNA. As with Group IV viruses, dsRNA intermediates are used to make copies of the genome and produce mRNA. In this case, the negative-stranded genome can be converted directly to mRNA. Additionally, full-length positive RNA strands are made to serve as templates for the production of the negative-stranded genome.

68. Group VI  viruses have diploid (two copies) ssRNA genomes that must be converted, using the enzyme reverse transcriptase, to dsDNA ; the dsDNA is then transported to the nucleus of the host cell and inserted into the host genome. Then, mRNA can be produced by transcription of the viral DNA that was integrated into the host genome . Group VII  viruses have partial dsDNA genomes and make ssRNA intermediates that act as mRNA, but are also converted back into dsDNA genomes by reverse transcriptase, necessary for genome replication.

69. Classification of Medical Parasites

70. Outline the classification of medically important parasites •Classification of medically important parasites – Helminthology . – Protozoology . –Entomology.

71. List types of medically important helminthes • Types of medically important helminthes – Trematodes – Cestodes –Nematodes •Intestinal nematodes •Tissue nematodes

72. Differentiate between types of helminthes A- Trematodes (Flukes) 1-General morphological characters. •Hermaphrodite except blood flukes (Unisexual) • Leaf-like, flattened and bilaterally symmetrical •There is no body cavity. 2-Organs of fixation : Almost all have 2 suckers, oral (at the anterior end, around the mouth) and ventral (on the ventral surface). Heterophyes has its genital pore surrounded by a muscular ring called genital sucker.

73. A- Trematodes 3- Habitat: T hey have different habitat; intestinal, hepatic, blood and pulmonary flukes. 4-General outline of the life cycle. • Adult → egg → miracidium → sporocyst → redia → cercaria → metacercaria → adult. •Egg is operculated , and should reach to a water source to hatch. •The first intermediate host is snail, and the second (if present) is marine creature. •Except for Schistosoma , egg has a spine, no redia and no metacercaria .

74. A- Trematodes 5-Important stages in the life cycle. • The diagnostic stage is the egg. •The infective stage is the encysted metacercaria except in Schistosoma , it is the cercaria . •The mode of infection is by ingestion of food contaminated with the infective stage except in Schistosoma , it is by skin penetration of the cercaria .

75. B- Cestodes (tapeworms) 1-General morphological characters. Hermaphrodite. Ribbon-like flattened and bilaterally symmetrical. There is neither body cavity nor digestive tract. The body is formed of 3 parts: • Head ( Scolex ) which is provided by organs of attachment. • Neck is composed of actively dividing cells (stem cells) and it is responsible for giving rise to new segments. • Body is composed of several segments (Immature, Mature and Gravid segments).

76. 2-Organs of fixation: 2 types: •Suckers (4) with or without hooks that are arranged in one or more circles on the apex of the scolex called “ rostellum ”. • Bothria (2) that take the form of grooves. 3-Habitat: They all (without exception) are intestinal parasites. B- Cestodes (tapeworms)

77. 4-General outline of the life cycle. • Adult → egg → cysticercus (the larval stage) → adult, Except for D. latum , give oval operculated egg containing hexacanthembryo ( coracidium ). •All cestodes require one intermediate host (usually vertebrate), except D. latum requires two intermediate hosts. H. nana does not require an intermediate host. B- Cestodes (tapeworms)

78. 5-Important stages in the life cycle. •The diagnostic stage is the egg. •The infective stage is the last larval stage which is different according to: No intermediate host (H. nana): Egg. 1 intermediate host (Other cestodes ): Cysticercus 2 intermediate hosts (D. latum ): Pleurocercoid . •The mode of infection is by ingestion of food contaminated with the infective stage. B- Cestodes (tapeworms)

79. C-Nematodes (cylindrical worms) 1-General morphological characters. Bilateral symmetrical Has body cavity Separate sexes Elongate and cylindrical 2-Organs of fixation are present in the mouth and buccal cavity as lancets and teeth. 3-Habitat: Intestinal (small and large) and tissue nematodes. 4-General outline of the life cycle. •Adult → egg → larva → adult. •Tissue nematodes are viviparous (lay larvae). Larva molts its cuticle 3 times.

80. C-Nematodes (cylindrical worms) Intestinal nematodes Tissue nematodes Larva 2 rhabditiform and filariform . Larva called Microfilaria Intermediate host No intermediate host Essential to complete life cycle Egg Immature except Entrobious vermecularis No egg

81. C-Nematodes (cylindrical worms) Intestinal nematodes Tissue nematodes Diagnostic stage Egg or Larva Microfilaria Infective stage Egg containing larva or filariform larva Infective microfilaria Mode of infection Ingestion of food contaminated with the infective stage or skin penetration Ingestion or bite of the infective vector 5-Important stages in the life cycle.

82. Types of medically important protozoa Pseudopodia. Flagellates. Ciliates. Coccidia .

83. 1- General characters of protozoa •Body is formed of cytoplasm and nucleus. •Cytoplasm is differentiated into ectoplasm and endoplasm. •Nucleus contains karyosome and peripheral chromatin.

84. 1- Pseudopodia Locomotororgans : Pseudopodia. Habitat: Intestinal and free living. General outline of the life cycle and important stages: Trophozoite and cyst. 2- Ciliates Locomotororgans : Cilia. Habitat: Intestinal. General outline of the life cycle and important stages: Trophozoite and cyst.

85. 3- Flagellates General morphological characters: Flagella as Locomotororgans . Habitat:Intestinal , urogenitaland , blood. General outline of the life cycle and important stages: •Intestinal and urogenitalflagellates : Trophozoite and cyst. •Blood flagellates: • Leishmania : Amastigotes (in human) and promastigotes (Vector). • Trypanosoma:Trypomastigotes (human) and Epimastigotes (Vector).

86. 4-Coccidia Locomotororgans:They are sporulated . They are members of Apicomplexa . Habitat: Intestinal, tissue and blood. General outline of the life cycle: Gametogony (Sexual reproduction). Important stages in the life cycle: Sporozoite , Schizont , merozoite , gametocytes, oocyst .