Nematodes Parasitology Chapter 2 PDF

**Chapter 2:** NEMATODES **Helminths** \- parasitic worms \- under the kingdom Animalia \- complex, multicellular eukaryotic organisms Helminths, which occur as parasite in humans, belong to two (2) phyla: a.) Phylum Nematoda: AKA Roundworms b.) Phylum Platyhelminthes: AKA Flatworms **a) Ces...

**Chapter 2:** NEMATODES **Helminths** \- parasitic worms \- under the kingdom Animalia \- complex, multicellular eukaryotic organisms Helminths, which occur as parasite in humans, belong to two (2) phyla: a.) Phylum Nematoda: AKA Roundworms b.) Phylum Platyhelminthes: AKA Flatworms **a) Cestodes (Tapeworm)** **b) Trematodes (Flukes)** **Phylum Nematoda (Roundworms)** \- [Elongated], [cylindrical unsegmented worms] with [tapering ends] \- [Bilaterally symmetrical] with secondary *triradiate* symmetry at the anterior end \- Anterior end may be equipped with [hooks, teeth, plates, setae and papillae] - ***Alimentary Tract*** - **Mouth**: surrounded by lips or papillae; equipped with teeth or plates that leads into a tubular or funnel- shaped buccal cavity - **Esophagus**: Cellular/ muscular; bulbous posteriorly - **Intestine** is lined with a single layer of columnar cells and leads to the rectum - **Male**: rectum and ejaculatory duct open into the cloaca - **Female**: anus - Around the **anal orifice** are papillae, the number and pattern aid in species identification - ***Nervous System*** - Anterior nerve ring (brain) - Ventral and dorsal cord - ***Excretory system*** - Consists of [2 lateral canals] that lie in the lateral longitudinal cords - **Reproductive System** - dioecious +-----------------------------------+-----------------------------------+ | MALE | FEMALE | +===================================+===================================+ | - Testes | - Uterus becomes coiled, full | | | ova/larvae filling body | | - Seminal vesicle Spicule | cavity | | | | | - Papillae: pre anal and post | - Seminal receptacle | | anal, sometimes present | | | | - Oviduct | | | | | | - Ovary | | | | | | - Vulva and vagina | +-----------------------------------+-----------------------------------+ **Definitive Host** - 3 routes by which the host become infected: - Ingestion of eggs - Eggs or larvae reach an infective stage - Eggs or larvae transmitted to a new host by insect vectors **General Life Cycle of Nematodes** Two phases: 1. Parasitic - Takes place inside the definitive host. - *Egg*, L1, L2, *L3* 2. Pre-parasitic - Free-living; lives in the environment - *L3*, L4, L5, Adult, *Egg* Egg-hatching: - Temperature - Moisture levels in the external environment **L1** \- feeds on bacteria \- Rhabditiform Larvae Molting/ Ecdysis a. **Exsheathment** -- old cuticle loosens and rupture; larva wiggles out of the cuticle b. **Synthesis** -- generation of new cuticle by the hypodermis of parasite \- occurs *[four times]* during each life cycle (at the end of each larval stage) **L2 -- L4** \- Filaform Larvae \- L2: Molting- Shedding of cuticle **L5** \- sexually immature adult **Adult** **Classification** **Based on the *presence of a sensory organ*:** - **Aphasmidia/ Adenophorea (TCT)** - *Trichinella spiralis* - *Capillaria* species - *Trichuris trichiura* - **Phasmidia/Secernentea (AH SEF)** - *Ascaris lumbricoides* - Hookworm species - *Strongyloides stercoralis* - *Enterobius vermicularis* - Filariae **Based on the *location of Adult Worm* in the Body:** - **Intestinal Nematodes:** - Small intestine: Hookworm species, *Ascaris lumbricoides*, *Strongyloides stercoralis,* - Large intestine: *Trichuris trichiura, Enterobius vermicularis* - **Tissue Nematodes:** - Lymphatic: *Wuchereria bancrofti, Brugia malayi, Brugia timori* - Subcutaneous: *Loa loa,* *Onchocera volvolus, Dracunculus medinensis* - Conjuctiva: *Loa loa* **Based on the *Mode of Transmission*:** - **Ingestion** - Eggs: *Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis* **[(ATE)]** - Larvae within intermediate host: *Dracunculus medinensis, cyclops* - Encysted larvae in muscle: *Trichinella spiralis* - **Penetration of Skin:** *Hookworm spp., Strongyloides stercoralis* - **Blood-Sucking Insects:** Mosquito, Filarial worms - **Inhalation of Dust with Eggs:** *Ascaris lumbricoides, Enterobius vermicularis* **Based on *whether they lay eggs or larvae*:** - **Oviparous** -- lays eggs - Unsegmented eggs: *Ascaris lumbricoides* - Segmented eggs: Hookworm species - Egg containing larvae: *Enterobius vermicularis* - **Viviparous**: do not lay egg - *Trichinella spiralis* - *Wuchereria bancrofti* - *Brugia malayi* - *Brugia timori* - *Dracunculus medinensis* - **Ovoviviparous**: lays eggs that contain fully formed larvae which hatch out immediately. - *Strongyloides stercoralis*