Nematodes are one of the most abundant metazoans on Earth, with over 25,000 known species. They occupy nearly every habitat and play important roles as free-living organisms, plant parasites, and parasites of humans and other animals. Nematodes have been used extensively as model organisms in fields like genetics and developmental biology due to traits like small size, short lifecycles, and fully sequenced genomes. Major nematode parasites of humans include roundworms, pinworms, hookworms, filarial worms, and guinea worms, which collectively infect over a billion people globally.

1. The World of Nematodes
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2. Lecture I
Introduction to Nematodes
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3. NematodesNematodes
nemanema= thread;= thread; oidesoides = resembling= resembling
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4. Nematode HabitatsNematode Habitats
““If all the matter in the universe except the nematodes wereIf all the matter in the universe except the nematodes were
swept away, our world would still be dimly recognizable…..swept away, our world would still be dimly recognizable…..
we would find its mountains, hills, valleys, rivers, lakes andwe would find its mountains, hills, valleys, rivers, lakes and
oceans represented by a film of nematodesoceans represented by a film of nematodes””
………………………………N. A. CobbN. A. Cobb
Nematodes dwell in all types of habitats on earth – fromNematodes dwell in all types of habitats on earth – from
ocean depths to tops of mountains, from hot waterocean depths to tops of mountains, from hot water
springs to icy arctic and antarctic, from barren lands tosprings to icy arctic and antarctic, from barren lands to
cultivated fields , and from meadows to tropicalcultivated fields , and from meadows to tropical
forests.forests.
Nematodes occupy any conceivable habitat on this earthNematodes occupy any conceivable habitat on this earth
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5. Placement in AnimalPlacement in Animal
KingdomKingdom
• InvertebratesInvertebrates
• ProtozoaProtozoa
• PoriferaPorifera
• CoelenterataCoelenterata
• PlatyhelminthesPlatyhelminthes
• AschelminthesAschelminthes
• ArthropodaArthropoda
• AnnelidaAnnelida
• MolluscaMollusca
• EchinodermataEchinodermata
• VertebratesVertebrates
• PiscesPisces
• AmphibiaAmphibia
• ReptiliaReptilia
• AvesAves
• MammaliaMammalia
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6. The HelminthsThe Helminths
• PlatyhelminthesPlatyhelminthes
• TrematodesTrematodes
• Flat wormsFlat worms
• Liver fluke,Liver fluke,
e.g.,e.g., Fasciola hepaticaFasciola hepatica
• CestodesCestodes
• Tape wormsTape worms
• e.g.,e.g., Taenia soliumTaenia solium
• Aschelminthes /Aschelminthes /
NemathelminthesNemathelminthes
• NematodaNematoda
• RotiferaRotifera
• PriapulidaPriapulida
• GastrotrichaGastrotricha
• KinorhynchaKinorhyncha
• NematomorphaNematomorpha
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7. Current statusCurrent status
• Phylum Nematoda or NemataPhylum Nematoda or Nemata
• Contains exclusively NematodesContains exclusively Nematodes
• Nematodes are numerically most abundantNematodes are numerically most abundant
among all the metazoans on earthamong all the metazoans on earth
• Nematodes rank second (next to insects) inNematodes rank second (next to insects) in
terms of number of species (diversity ofterms of number of species (diversity of
forms). About 25000 species are known tillforms). About 25000 species are known till
date, out of an estimated 500000 species ofdate, out of an estimated 500000 species of
nematodesnematodes
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8. Types of NematodesTypes of Nematodes
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9. Relative abundance
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10. Free living nematodesFree living nematodes
Not economically important, Microscopic, Saprophagous,Not economically important, Microscopic, Saprophagous,
Microbivorous,Microbivorous,
Omnipresent – Terrestrial, Aquatic (Marine, Fresh water)Omnipresent – Terrestrial, Aquatic (Marine, Fresh water)
• Marine nematodesMarine nematodes
• ChromadoraChromadora
• ChaetostomaChaetostoma
• DeontostomaDeontostoma
• Soil & Fresh Water nematodesSoil & Fresh Water nematodes
• RhabditisRhabditis
• PlectusPlectus
• DorylaimusDorylaimus
• NygolaimusNygolaimus
• MononchusMononchus
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11. Nematodes as Biological ModelsNematodes as Biological Models
Free-living bacterial feeder rhabditid nematodes are usedFree-living bacterial feeder rhabditid nematodes are used
as model systems in diverse scientific fieldsas model systems in diverse scientific fields
Examples:Examples: Caenorhabditis elegans, C. briggsae, Turbatrix aceti,Caenorhabditis elegans, C. briggsae, Turbatrix aceti,
Panagrellus redivivusPanagrellus redivivus
ApplicationsApplications
• GeneticsGenetics
• Developmental BiologyDevelopmental Biology
• NutritionNutrition
• Environmental toxicologyEnvironmental toxicology
• PharmacologyPharmacology
• GerontologyGerontology
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12. Advantages of using nematodes asAdvantages of using nematodes as
model systemsmodel systems
• Axenic and monoaxenic cultivation possibleAxenic and monoaxenic cultivation possible
• Adult hermaphrodite (self fertilizing)Adult hermaphrodite (self fertilizing)
• Short generation time (ca. 3 days)Short generation time (ca. 3 days)
• Large progeny (300 per individual)Large progeny (300 per individual)
• Small size (1 mm long)Small size (1 mm long)
• Transparent body wallTransparent body wall
• Storage in liquid nitrogen possibleStorage in liquid nitrogen possible
• Handling large number of individuals in aHandling large number of individuals in a
reasonable spacereasonable space
• Ease of genetic manipulation (induced mutation)Ease of genetic manipulation (induced mutation)
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13. Applications in GeneticsApplications in Genetics
CharacteristicsCharacteristics of C. elegansof C. elegans
• Small genome sizeSmall genome size (haploid DNA content 8x10(haploid DNA content 8x1077
basebase
pairs)pairs)
• Populations are driven to homozygosity, easyPopulations are driven to homozygosity, easy
to isolate clones of isogenic animalsto isolate clones of isogenic animals
• New mutants automatically madeNew mutants automatically made
homozygous in one generationhomozygous in one generation
• Mutant stocks readily established from singleMutant stocks readily established from single
individualindividual
• Mutants are fertileMutants are fertile
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14. MutantsMutants
Mutants cloned, classified and assigned a code nameMutants cloned, classified and assigned a code name
e.g., “e.g., “Dpy- 45 (e 420) IIDpy- 45 (e 420) II” . The code name includes” . The code name includes
A mutant nameA mutant name e 420e 420 wherewhere ee is the lab code to trace its origin,is the lab code to trace its origin, 420420
is one of the series of mutants from that lab.is one of the series of mutants from that lab.
A gene nameA gene name dpy- 45dpy- 45, where, where dpydpy (dumpy) is phenotypic category(dumpy) is phenotypic category
andand 4545 one of the genes in that categoryone of the genes in that category
A linkage group -A linkage group - IIII
Caenorhabditis Genetic CenterCaenorhabditis Genetic Center
National Institute of Aging, Univ. of Missouri, Columbia, USANational Institute of Aging, Univ. of Missouri, Columbia, USA
responsible for maintenance ofresponsible for maintenance of C. elegansC. elegans genetic map, geneticgenetic map, genetic
nomenclature, storage, distribution of mutantsnomenclature, storage, distribution of mutants
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15. NEMATODES ASNEMATODES AS
PARASITESPARASITES
PARASITES
On Human Beings On Vertebrates On Invertebrates On Plants
Medical
Sciences
Veterinary
Sciences
Agricultural
Sciences
Agricultural
Sciences
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16. NEMATODE PARASITE S Of HUMANNEMATODE PARASITE S Of HUMAN
BEINGSBEINGS
• Known since ancient times – mention ofKnown since ancient times – mention of
human parasites inhuman parasites in Vedas,Vedas, first to befirst to be
recordedrecorded
• Big in size, easily visibleBig in size, easily visible
• Examples:Examples:
• Intestinal round wormIntestinal round worm Ascaris lumbricoidesAscaris lumbricoides
• Pin wormPin worm Enterobius vermicularisEnterobius vermicularis
• Filarial wormFilarial worm Wucheraria bancroftiWucheraria bancrofti
• Hook wormsHook worms Ancylostoma duodenaleAncylostoma duodenale,,
Necator americanusNecator americanus
• Guinea wormGuinea worm Dracunculus medinensisDracunculus medinensis
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17. NEMATODE PARASITE S Of HUMANNEMATODE PARASITE S Of HUMAN
BEINGSBEINGS
Ascaris lumbricoides -Ascaris lumbricoides - The Intestinal roundwormThe Intestinal roundworm
- Approx 25% world population is infected with- Approx 25% world population is infected with AscarisAscaris
- Each female lays ca. 2.7 million eggs per day in faeces- Each female lays ca. 2.7 million eggs per day in faeces
- Causes anemia and leads to intestinal blockage- Causes anemia and leads to intestinal blockage
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18. NEMATODE PARASITE S Of HUMANNEMATODE PARASITE S Of HUMAN
BEINGSBEINGS
Enterobius vermicularisEnterobius vermicularis
Commonly known as Pin wormCommonly known as Pin worm
Parasite of caecumParasite of caecum
Cause itching in anal areaCause itching in anal area
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19. NEMATODE PARASITES Of HUMANNEMATODE PARASITES Of HUMAN
BEINGSBEINGS
Dranunculus medinensisDranunculus medinensis
Commonly known as Guinea wormCommonly known as Guinea worm
It is a parasite of sub-cutaneous tissuesIt is a parasite of sub-cutaneous tissues
Ca. 50 million people in Africa and Asia areCa. 50 million people in Africa and Asia are
infected with this nematodeinfected with this nematode
Guinea worm forming blisters on the limb
Guinea worm partially emerging out of the blister
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20. NEMATODE PARASITES Of HUMANNEMATODE PARASITES Of HUMAN
BEINGSBEINGS
Wucheraria bancroftiWucheraria bancrofti - The filarial worm- The filarial worm
Causes Elephantiasis/FilariasisCauses Elephantiasis/Filariasis
• Parasite of lymphatic systemParasite of lymphatic system
• Causes inflammation of limbs andCauses inflammation of limbs and
genital organsgenital organs
• Prevalent in coastal areas of southPrevalent in coastal areas of south
and east Indiaand east India
• Transmitted by mosquitoesTransmitted by mosquitoes
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21. NEMATODE PARASITE S OfNEMATODE PARASITE S Of
VERTEBRATESVERTEBRATES
• Big in size and visible to naked eyes
• Some forms are common to human beings
• Examples
Trichuris sp. – The whip worm
in alimentary canal of dogs, pigs,
ruminants
Dioctophyma renale – the giant kidney worm,
in dog, amy reach up to 90 cm
Haemonchus contortus
in alimentary canal of sheep, goat, cattle
Trichostrongylus spp.
in alimentary canal of ruminants,
horses, sheep, goats
Ascaridia galli
in intestine of chicken
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22. NEMATODE PARASITE S OfNEMATODE PARASITE S Of
INVERTEBRATESINVERTEBRATES
The Mermithids
• Mermis nigrescens – parasite of grasshoppers and locusts
• Romanomermis culicovorax – parasite of mosquito larvae
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23. NEMATODE PARASITE S OfNEMATODE PARASITE S Of
INVERTEBRATESINVERTEBRATES
The Entomopathogenic nematodes – EPNs
• Used for biological control of insect pests of crops, commercial
formulations available
• Kill diverse group of insects
• Carry pathogenic bacteria inside, release in insect haemocoel
• Bacteria cause septicaemia, insects die within 2-3 days
• Examples:
Steinernema spp. carry bacterium Xenorhabdus spp.
Heterorhabditis spp. carry bacterium Photorhabdus spp.
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24. Entomopathogenic NematodesEntomopathogenic Nematodes
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25. NEMATODES ASNEMATODES AS
PARASITESPARASITES
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26. NematologyNematology
• Agricultural Nematology, Plant Nematology, PhytonematologyAgricultural Nematology, Plant Nematology, Phytonematology
• Branch of Plant Protection, on par with Entomology and PlantBranch of Plant Protection, on par with Entomology and Plant
PathologyPathology
• First PPN discovered on in 1743First PPN discovered on in 1743
• Economic importance of PPNs realized only after 1940s; reasonsEconomic importance of PPNs realized only after 1940s; reasons
• Microscopic size of PPNsMicroscopic size of PPNs
• Hidden mode of life, either in soil or rootsHidden mode of life, either in soil or roots
• No clear cut symptoms on plantsNo clear cut symptoms on plants
• Lack of trained personnelLack of trained personnel
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