Parasitology Lecture Notes PDF

# Parasitology - area of biology concerned with the phenomenon of dependence of one living organism on another ## What is a parasite? - a pathogen that simultaneously injures and derives sustenance from its host - some parasites are commensals neither benefit nor harm their host - for example...

# Parasitology - area of biology concerned with the phenomenon of dependence of one living organism on another ## What is a parasite? - a pathogen that simultaneously injures and derives sustenance from its host - some parasites are commensals neither benefit nor harm their host - for example: *Entamoeba coli* # Mutualism - a symbiosis in which 2 organisms mutually benefit from each other - e.g. termites and flagellates in their digestive system, which synthesize cellulose to aid in breakdown of ingested wood. # Parasitism - a symbiotic relationship where one organism (the parasite), lives in or on another (the host), depending on the latter for its survival and usually at the expense of the host - e.g. *Entamoeba histolytica* derives nutrition from the human host and causes amebic dysentry # Classification of Parasites ## According to habitat or mode of development: - **Endoparasite**: a parasite living inside the body of a host; presence of an endoparasite in a host is called an infection - **Ectoparasite**: a parasite living outside the body of a host; presence of an ectoparasite inside the host is called an infestation. ## According to the life cycle: - **Obligate parasites** need a host at some stage of their life cycle to complete third development and to propagate their species - e.g. tapeworms depend entirely upon their host for existence - **Facultative parasite**: may exist in a free living state or may become parasitic when the need arises - e.g. leeches feed on blood on their hosts but when released in aquatic environment survive as free living organisms - **Accidental or Incidental parasite**: establishes itself in a host where it does not ordinarily live - e.g. Diplydiasis in humans is accidental - **Permanent parasite**: remains on or in the body of the host for its entire life cycle - e.g. Most roundworms are permanent parasites and live their entire adult lives in their hosts. - **Temporary parasite**: lives on the host only for a short period - e.g. ticks, flea and mites - **Spurious parasite**: a free-living organisms has passes through the digestive tract without infecting the host - e.g. Isosopora # Host - classified based on their role in the life cycle of parasite - **Definitive or final host**: one in which the parasite attains sexual maturity - e.g. humans are the definitive host in taeniasis. - **Intermediate host**: harbors the asexual or larval stage of the parasite - e.g. Pigs or cattle as intermediate hosts of *Taenia spp*, while snails are hosts of *Schistosoma spp.* - **Paratenic host**: one in which the parasite does not develop further to later stages. However, the parasite remains alive and is able to infect another susceptible host. - e.g. *Paragonimus* metacercariae in raw wild boar meat can pass through the intestinal wall of humans and complete its development. - **Reservoir hosts**: allow parasite's life cycle to continue and become additional sources of human infection - e.g. pigs are reservoirs of *Balantidium coli* # Vectors - responsible for transmitting the parasite from one host to another. - It could be classified into: - **Biologic Vector**: transmits the parasite only after the latter has completed its development within the host - e.g. *Aedes* sucks blood form a patient with fliariasis, the parasite undergoes several stages of development from the first stage larva to 3rd stage larva before it is transmitted to another susceptible host. - **Mechanical vector**: transports the parasite without changes - e.g. flies and cockroaches that feed on fecal material may carry enteric organisms and transfer these to food. # Carrier - harbors a pathogen without manifesting any signs and symptoms # Exposure - process of inoculating an infective agent # Infection - connotes the establishment of the infecting agent in the host # Incubation period (clinical incubation period) - Period between infection and evidence of symptoms # Pre-patent period (biologic incubation period) - Period between acquisition of this parasite and evidence or demonstration of infection. # Autoinfection - When an infected individual becomes his own direct source of infection. - e.g. enterobiasis: infective eggs end up in the hands by scratching the perianal area where the gravid females lay their eggs. - As seen in the life cycles of *E. vermicularis*, *Hymenolipsis nana* and *Strongyloides stercoralis* # Superinfection or Hyperinfection - when the already infected individual is further infected with the same species leading to massive infection - alteration in the normal life cycle of *Strongyloides* results in a large increase in worm burden, severe debilitation and death. # Sources of Infection 1. Contaminated soil and water. - Most common lack of sanitary toilets & the use of human and animal excreta as fertilizer favor infection with ascaris, hookworm. - Water contaminated with cysts of amoebae or flagellates as well as cercariae of *Schistosoma*. 2. Food. - Food may contain the infective stage of the parasite. 3. Arthropods - e.g. mosquitoes as vectors of malaria and filaria parasites. 4. Other animals - (wild or domesticated) may harbor the parasite: e.g. cats are direct sources of *Toxoplasma* infection # Modes of Transmission 1. Mouth - The mouth is the most likely portal of entry for most cestodes, trematodes and protozoans are foodborne. 2. Skin Penetration - e.g. hookworms and *Stronglyoides* 3. Arthropods - As vectors, they transmit parasites through bites. For example: malaria, filarial, leishmaniasis and trypanosomaiasis 4. Congenital Transmission - *Toxoplasma gondii* trophozoites can cross the placenta. 5. Transmammmary Infection - Infection with *Ancylostoma* and *Strongyloides*. The parasite maybe transmitted through the mother's milk. 6. Inhalation - Inhalation of airborne eggs of *Enetorbius*. 7. Sexual Intercourse - For example: *Trichomonas vaginalis*. # Parasitic Infections ## Multicellular Metazoan: - **Helminthes:** - Leeches - Round worms (*Nemathelminthes*) - Flat worms (*Platyhelminthes*) - Flukes (*Trematodes*) - Monogenetic - Digenetic - Tape worms (*Cestodes*) - Eucetsoda - Cotyloda ## Unicellular Protozoan: # Introduction - All animal organisms are related to one another, closely or remotely, and the study of the complex systems of inter-relationship is called systematics. - As an instance, the taxonomic status of one of the common abomasal parasites of ruminants may be expressed as shown below: | Feature | Description | | --------------- | -------------------- | | Kingdom | Animalia | | Phylum | *Nemathelminthes* | | Class | *Nematoda* | | Order | *Strongylida* | | Suborder | *Strongylina* | | Superfamily | *Trichostrongyloidea* | | Family | *Trichostrongyloidae* | | Subfamily | *Haemonchinae* | | Genus | *Haemonchus* | | Species | *contortus* | - Three phyla will be discussed: *Platyhelminths* (flatworms), *Nemathelminthes* (round worms) and *Acanthocephala* (thorny-headed worms). # Platyhelminthes - This phylum contains 2 classes of parasitic flatworms - the *Trematoda* and the *Cestoda*. ## Class: Trematoda (Flukes) - The class *Trematoda* falls into two main subclasses - the *Monogenea*, which have a direct life cycle, and the *Digenea*, which require an intermediate host. - The adult digenetic trematodes, commonly called 'flukes', occur primarily in the bile ducts, alimentary tract and vascular system. - Most flukes are flattened dorsoventrally. have a blind alimentary tract, have usually 2 suckers, for attachment and are hermaphrodite. - Depending on the predilection site, the eggs pass out of the final host usually in feces or urine, and the larval stage develop in the intermediate host "**snail**". - For a few species, a second intermediate host is involved, but the mollusc "**snail**" is essential for all members of the group. # Digenea Structure and Function - The adult possesses two suckers for attachment. - The oral sucker at the anterior end surrounds the mouth and the ventral, as the name indicates, is on that surface. - The body surface is a tegument which is absorptive and is often covered with spines. - The muscles lie immediately below the tegument. - There is no body cavity and the organs are packed in a parenchyma. - The digestive system is simple, the oral opening leading into a pharynx, oesophagus and a pair of branched intestinal caeca which end blindly. - The excretory system consists of a large number of ciliated flame cells, which impel waste metabolic products along a system of tubules which ultimately join and open to the exterior. - The nervous system is simple, consisting of a pair of longitudinal trunks connecting anteriorly with two ganglia. # External Fluke Structure - Diagram of external fluke structure. Labels include: **oral sucker**, **cephalic cone**, **papilla on cuticle**, **genital papilla**, **genital pore**, **genital sucker**, **genital calyx**, **ventral sucker**, **ventral surface**, **spines on cuticle**, **cuticle**, **excretory pore**. - Diagram of fluke reproductive system with labels including: **gynecophoric canal**, **oral sucker**, **acetabulum**. # Internal Fluke Structure - Diagram of fluke internal anatomy with labels including: **oral sucker**, **pharynx**, **oesophagus**, **genital pore**, **gonopore**, **cirrus gland**, **cirrus pouch**, **ejaculatory duct**, **pars muscularis, **genital atrium**, **pars prostatica**, **seriaal vesicle**, **retrator**, **cirrus sac**, **vas deferens**, **uterus**, **vitellaria**, **lateral diverticulum**, **ovary**, **vitelling duct**, **seminal receptacle**, **laurer's canal**, **ootype**, **mehlis gland**, **excretory system**, **excretory vesicle**, **testes**, **excretory bladder**, **excretory pore**, **caeca**. # Digestive System of a Fluke - Diagram of fluke digestive system with labels including: **oral sucker (mouth)**, **pharynx**, **digestive caeca - straight**, **digestive caeca - undulatiing**, **digestive caeca - branched**. # Reproductive System of a Fluke - **Male:** - Diagram of the male fluke reproductive system with labels including: **genital opening**, **genital atrium**, **cirrus pouch**, **cirrus**, **seminal vesicle**, **vas deferens**, **vas efferens**, **testes**. - Diagram of the male fluke reproductive system with labels for **shape** including: **individual testes**, **oval**, **lobate**, **dendritic**. - Diagram of the male fluke reproductive system with labels for **position** including: **tander**, **oblique**, **para**. - **Female:** - Diagram of the female fluke reproductive system with labels including: **genital atrium**, **egg**, **uterus**, **mehlis glands**, **ootype**, **vitelline duct**, **laurer's canal**, **seminal receptacle**, **ovary**, **vitellaria**. - Diagram of the female fluke reproductive system with labels including **male system joing**. # Schistosoma - Diagram of *Schistosoma* reproductive system with labels including: **oral sucker**, **pharynx**, **oesophagus**, **genital pore**, **cirrus**, **cirrus sac**, **ejaculatory duct**, **pars muscularis**, **pars prostatica**, **seriaal vesicle**, **vas deferens**, **uterus**, **vitellaria**, **ovary**, **laurer's canal**, **mehlis gland**, **ootype**, **vitelline duct**, **seminal receptacle**. # *Fasciola hepatica* Life Cycle - Diagram of *Fasciola hepatica* life cycle with labels including: **adult in biliary passages**, **egg in faeces (yolk mass)**, **deposited in water**, **9 to 15 days development in water**, **miracidium - free**, **penetrates liver**, **burrows through intestinal wall**, **ingested by host**, **metacercaria on water plants - bark or free floating**, **cercaria swarming - seasonal (Aug. and Ser.)**, **enters snail - Lymnaea truncatula, Lymnaea spp.**, **larval stages - 32-54 days - sporocyst, mother - redia, daughter redia, cercaria - temperature dependent.** # Veterinary Parasitology - Hand drawn diagrams of: - **Schistosoma** with labels "Schistosoma" - **Dicrocoelium** with labels "DicroGleum" - **Parempiotium/Fasciola** with labels "Parempliotiseum/Fasciolar" - **Leptocercus Cercaria** with labels "Leptocercus Cercarica" - **Cpijmatata** (or **Cavavinin**) with labels "Cpijmatata (or Cavavinin)" - **Heterophys Lophdec Cercaria** with labels "Heterophyl Lophdec Cercaria" - **Echinastoma Cercaria** with labels "Echinastoma Cercaria" # Lymnaea truncatula/Fasciola hepatica - Hand drawn diagrams of: - **Lymnaea L. trunctanta** with labels "Lymnea L. trunctanta" - **Canilder** with labels "Canilder" - **Chepatics stagnalis (gigantic)** with labels "Chepatics stagnalis (gigantic)" - **Dicro Gleum** with labels "Dicro Gleum" - **Cpijmatata** (or **Cavavinin**) with labels "Cpijmatata (or Cavavinin)" - **Heterophyl Lophdec Cercaria** with labels "Heterophyl Lophdec Cercaria" - Text includes: - "Parasitism" - "Commensalism" - "Symbiosis"