2022-2023 Parasitology 1 PDF

2022-2023 Lebanese University Faculty of Agricultural & Veterinary Sciences PARASITOLOGY 1 DR WALID DARWICHE...

2022-2023 Lebanese University Faculty of Agricultural & Veterinary Sciences PARASITOLOGY 1 DR WALID DARWICHE 3. Parasitic Adaptations 1 Definition:  “Any feature of an organism or its part which enables it to exist under conditions of its habitat is called adaptation”  Adaptations are mainly: To withstand the adverse conditions of the environment To use the maximum benefit of the environment Giraffes are well adapted to a life in a savannah. Their very long necks are an adaption to feeding at high levels in the treetops. DR. WALID DARWICHE 2 2 Dr. Walid Darwiche 1 2022-2023 Parasites show three level adaptations: 1. Morphological adaptations 2. Anatomical adaptations 3. Biological adaptations DR. WALID DARWICHE 3 3 I. MORPHOLOGICAL ADAPTATIONS DR. WALID DARWICHE 4 4 Dr. Walid Darwiche 2 2022-2023 A. SIZE 1. Relative to the host ▪ Typically, parasites are much smaller than their host. Example: the large liver fluke and the cow. DR. WALID DARWICHE 5 5 2. Compared to free species. In a taxonomic group, the parasites will be larger than the free individuals of the same group. Examples: Ticks (1cm when they are full of blood) are much larger than dust mites (a few hundred microns) even though they are part of the same taxonomic group. The free nematodes living in the ground or in the grass are roundworms much smaller than their parasitic "cousin", like the roundworm which can reach 30cm. DR. WALID DARWICHE 6 6 Dr. Walid Darwiche 3 2022-2023 3. Depending on gender. Often, females are larger than males (this is not always the case). This is due to the development of the gonads (uterus and ovaries) and allows the parasite to lay thousands of eggs at a time. DR. WALID DARWICHE 7 7 B. FORM  The parasite will have a different shape depending on its location in the host.  There are three classes of parasites: Ectoparasite – The parasitic organism that lives on the outer surface of its host, e.g. lice, ticks, mites etc. Endoparasite – The parasites that live inside the body of their host, e.g. Entamoeba histolytica, Taenia solium, Toxoplasma that live in the tissues, etc. Mesoparasite- The parasites living in an intermediate position, being half- ectoparasites and half-endoparasites. eg. Cymothoa exigua, or the tongue- eating louse, is a parasitic crustacean. This parasite enters fish through the gills, and then attaches itself to the fish's tongue; taenia which live in cavities or organs having an opening to the outside environment (such as the bladder, lungs, digestive tract, etc.) DR. WALID DARWICHE 8 8 Dr. Walid Darwiche 4 2022-2023 b sir huwe mahal l lsen Cymothoa exigua DR. WALID DARWICHE 9 9 These three classes are not clearly defined because some parasites can be endoparasites and then mesoparasites during their development cycle. In general, the shape of the parasites will be adapted to their location:  Form of ectoparasites: mtl l fleas lezim tkun rafi3a ktir la tmshe byn l sha3r ticks Flattened dorsoventrally or latero-laterally mtl mam3ousin la y3alli2 w ma ybrum The elongation is in the direction of "aerodynamics" Examples: aquatic ectoparasites grip to the scales of a fish so as to be in the direction of the current the dog and cat flea is flattened side-to-side the human louse is flattened dorsoventrally DR. WALID DARWICHE 10 10 Dr. Walid Darwiche 5 2022-2023  Form of mesoparasites: Flattened or circular body Often the elongation is important. It depends on the living environment: digestive tract, lungs or bladder (the parasites will rather be tangled in the bladder because there is less space) Examples: The taenia lives in the intestine, it is a flat and long worm that can reach several meters Nematodes and cestodes of man round DR. WALID DARWICHE 11 11  Form of endoparasites: They are mainly found in the liver or muscle. Globular body Rolled up on itself = tissue parasites Sometimes elongated body = parasite of blood vessels Examples: There are 3 larval forms of cestodes depending on their location in the intermediate host  Globular in the brain or between muscle fibers  In the form of hydatid cysts in the liver The trichina larvae are twisted, they are found in the muscles of the pork Worms can lodge in the heart chambers of dogs and measure up to twenty cm. DR. WALID DARWICHE 12 12 Dr. Walid Darwiche 6 2022-2023 DR. WALID DARWICHE 13 13 Hydatid cysts in the organs of cattle DR. WALID DARWICHE 14 14 Dr. Walid Darwiche 7 2022-2023 C. ATTACHMENT ORGANS 1. The rhizoids They allow, for example, Amyloodinium ocellatum to attach to the gills of fish. DR. WALID DARWICHE 15 15 2. The modified flagella This kind of organ is found on Leishmania sp., responsible for leishmaniosis: they allow it to attach itself to the host's cells. DR. WALID DARWICHE 16 16 Dr. Walid Darwiche 8 2022-2023 3. The suckers This fixing system is much more widespread than the previous two. The large liver fluke, Fasciola hepatica , has two suckers : a sucker at the mouth end and a ventral sucker. They are used to settle and to feed. Giardia lamblia uses her suckers (ventral disk) to press against the wall of the small intestine. It measures 12 m. DR. WALID DARWICHE 17 17 4. Mucus and sticky secretions. Ichthyophtirius multifillis secretes mucus to attach itself to the scales of fish. The louse uses an adhesive secretion to stick the nits to the hair and prevent them from being eliminated by the dog when it is scratching. Ichthyophthirius multifiliis (White Spot) Infections in Fish DR. WALID DARWICHE 18 18 Dr. Walid Darwiche 9 2022-2023 5. The modified appendages. The modified appendages are found in arthropods: they are claws, pincers or suckers. Psoroptes sp., agent of scabies, measures 500 to 700 m. At the end of its legs there are hooks and suckers. amel The human louse has pincers which allow it to catch the hair : they are made up of two “fingers” which adapt exactly to the shape of the hair. The sheep's "false louse" has an appendix modified by the absence of this appendix: it is the only one of its taxonomic group not to have wings, because it no longer needs them being a permanent parasite. It measures 0.5 to 1cm and attaches to the fleece of the sheep. DR. WALID DARWICHE 19 19 6. Hooks and thorns The human tapeworm has a crown of hooks in its terminal part, and suckers to hang in the intestine. The cestode of the dog and the cat has a several rings of hooks. Sarcoptic scabiei, the agent of scabies, has thorns and hooks on its back: they participate in the pathogenic action of the parasite. In fact, it digs tunnels in the horny layer of the epidermis: the clinical signs of its presence are a very strong inflammatory reaction and a very strong desire to scratch. DR. WALID DARWICHE 20 20 Dr. Walid Darwiche 10 2022-2023 7. The sinking The Tunga penetrans is found in tropical countries and burrows into the skin of dogs' paws (or human feet) and lays its eggs through the entrance opening. DR. WALID DARWICHE 21 21 II. ANATOMICAL ADAPTATIONS DR. WALID DARWICHE 22 22 Dr. Walid Darwiche 11 2022-2023 A. DIGESTIVE SYSTEM 1. Increase in intestinal volume and exchange surface This adaptation aims to facilitate the absorption of nutrients and is found especially in hematophagous parasites (which feed on the blood of their host). The digestive tract is much more developed than in non-blood-sucking insects. We find this type of adaptations in Ticks or Mosquitoes. The digestive tract can then dilate during a blood meal and the abdomen dilates at the same time. In the greater liver fluke, the cecum is very branched, which increases the exchange surface. By transparency, by observing the parasite under a microscope, we can see dark areas at the level of this cecum corresponding to the digested blood. The fluke does not have an anus. DR. WALID DARWICHE 23 23 2. Reduction / disappearance of the digestive system Sometimes the digestive tract can regress until it disappears. The parasite then feeds by pinocytosis through the tegument. Taenia saginata Absence of digestive tube in all Cestodes DR. WALID DARWICHE 24 24 Dr. Walid Darwiche 12 2022-2023 3. Case of hematophagous parasites Blood-sucking parasites such as Mosquitoes (Aedes Aegypti), Ticks or Fleas have an adaptation of their mouth parts : they become vulnerable, capable of stinging or biting the host to pass through the skin, injecting saliva which allows to lyse the tissues and finally pump the blood. DR. WALID DARWICHE 25 25 B. REPRODUCTIVE SYSTEM Internal parasites no longer have appendages to move around : the problem of reproduction of the parasite then arises. 1. Interconnection of sexual partners In the Trematode, the male lives surrounded around the female. They are in permanent mating. In nature, male and female Schistosoma mansoni worms pair up within the host DR. WALID DARWICHE 26 26 Dr. Walid Darwiche 13 2022-2023 2. Asexual multiplication It may be associated with a sexual multiplication. Production of schizogony by coccidia, protozoa living in the intestine. Echinococcus form a hydatid cyst in the liver. From a single egg, there is production and multiplication of a multitude of protoscolex which will give several thousand future parasites. 7a yshrhun b3den DR. WALID DARWICHE 27 27 Adult Cestodes have a segmented body: they are hermaphrodites, in each segment we find both ova and sperm. We can therefore see the Cestodes as a juxtaposition of autonomous segments in which sexual reproduction occurs. If we place ourselves at the level of the Cestode itself, it is asexual reproduction because there is no need for a partner to reproduce. DR. WALID DARWICHE 28 28 Dr. Walid Darwiche 14 2022-2023 3. Polyembryony (anecdotal) very rare We can take the example of the Hymenoptera Ageniaspis fuscicollis which produces several larvae from a single egg. Note: Often the reproductive tract of parasites will be much more developed than the reproductive tract of nonparasites of the same family. DR. WALID DARWICHE 29 29 III. BIOLOGICAL ADAPTATIONS DR. WALID DARWICHE 30 30 Dr. Walid Darwiche 15 2022-2023 A. INTRODUCTION, DEFINITIONS Biological cycle or cycle of development or evolutionary cycle of a parasite: Sequence of steps necessary for the development of an individual from one generation to another. Egg → larva → adult → sexual reproduction → egg of the next generation  We can break this cycle down into different stages: Host 1 Stage 1 Stage 2 Stage 3 Host 2 Stage 1: Exit from host 1 l eggs bytla3o Stage 2: life in another environment or another host (intermediary) Stage 3: Enter Host 2 DR. WALID DARWICHE 31 31 haw lal fehem, nefham l concept The parasite cycle is characterized by an alternation of living environments, a difficulty of transmission from one environment to another.  Example 1: Flea Larvae and Fleas on the Fleas on the hair of a dog Stage 1 nymph in the Stage 3 hair of environment another dog Passage from dog Finding a new host to the kennel bl eggs  Example 2: Ascaris Ascaris in the Eggs in the Ascaris in the intestine of a Stage 1 environment Stage 3 intestine of dog another dog Transformation into Ingestion by a new adult form host DR. WALID DARWICHE 32 32 Dr. Walid Darwiche 16 2022-2023 B. CONCEPT OF ECOLOGICAL NICHE OF A PARASITE  Ecological niche of a parasite: set of environmental conditions which each species “occupies” and to which that species is uniquely adapted.  It is an "n" dimensional space. Example: the ecological niche of a squirrel can be defined at several levels: the forest - the tree where it lives - the hollow of the tree in which it takes refuge - the different forests to which it has access and which it can visit to meet other squirrels. These are 4 dimensions of the ecological niche of the squirrel. The ecological niche of a parasite is conceptualized as a multidimensional space defined by the specific environmental conditions to which a given species is uniquely adapted This niche, often represented in an "n" dimensional framework, encompasses various dimensions relevant to the parasite's existence. DR. WALID DARWICHE 33 33 We will focus on a host space with four important dimensions for the veterinarian.  “individual” dimension: it is the patient in our practice  “population” dimension: if we have to intervene at the level of a cat house, or a breeding, where the transmission of the parasite can be done from one animal to another  "species" dimension: it is seldom used by the veterinarian and mainly concerns research and epidemiological surveillance.  “site” or “biotope” dimension: this is the place in the host where the parasite nests. Some parasites do not always live in the same place in the host: the “biotope” dimension will then vary over time. DR. WALID DARWICHE 34 34 Dr. Walid Darwiche 17 2022-2023 affeha DR. WALID DARWICHE 35 35 We must consider the notion of critical stage. Some stages of the cycle can be more difficult for parasites than others.  Ectoparasites live in the open air: they are used to the constraints of the external environment.  For them, the first two steps will be simple (leaving the host and living in the outside environment).  What will prove to be more complicated will be to find a new host.  =) For ectoparasites, the critical step is step 3. DR. WALID DARWICHE 36 36 Dr. Walid Darwiche 18 2022-2023  Mesoparasites live in the digestive tract of their host.  Step 1 is simple: they leave the host through the feces.  But, being used to an indoor environment that does not vary, they will have difficulty getting used to life in the outdoor environment (differences in T °C, hygrometry, precipitation, etc.).  They will then develop forms of resistance to the external environment, for example the formation of shells around the eggs, the passage through an intermediate host, etc.  Step 3 is simple, they just need to be swallowed by the host 2: if it is a Herbivore, by standing on blades of grass; if it is a Carnivore, by placing itself in one of its prey.  =) For mesoparasites, the critical step is step 2. DR. WALID DARWICHE 37 37  For endoparasites nested in muscles or other organs, all steps are critical.  To get out of the 1st host, there is a need for a break-in, to get into the 2nd host as well.  Finally, as with mesoparasites, life in the external environment can be difficult.  We can take the example of piroplasms (in the blood) which leave the host by mosquito or tick bite (with absorption of the blood) and enter the next host in the same way. Some parasites can live in arthropods as stage 2 in order to escape the constraints of the external environment.  =) For endoparasites, all steps are critical. DR. WALID DARWICHE 38 38 Dr. Walid Darwiche 19 2022-2023 C. CONCEPT OF HOST SEQUENCE: DIFFERENT TYPES OF CYCLES Host sequence:  this is the number of hosts operated successively during the cycle of the parasite.  The host sequence can be thought of as the longitudinal component of a parasite's life cycle.  It is a fixed number for a given parasite: 1, 2, 3 or even 4 exceptionally. Example: the great liver fluke (Fasciola Hepatica) needs 2 hosts to achieve its entire cycle. Its host sequence is equal to 2. DR. WALID DARWICHE 39 39 Depending on the value of the host sequence, different types of cycles are defined: Host sequence = 1 → Monoxenous cycle = 1 host cycle Examples: the flea only needs one host, a dog, to cycle. The same is for Toxocara canis, a parasite of dogs. Host sequence > 1 → Heteroxenous cycle = multiple host cycle ▪ Sequence = 2 → Dixenous cycle = 2 host cycle Examples: the liver fluke Fasciola hepatica. Taenia saginata, and all cestodes (tapeworms) in general ▪ Sequence = 3 → Trixenous cycle = three host cycle Examples: Dicrocolum lanceolatum, the small fluke Cycles with 4 hosts are so rare that they are not given a name. mn2ellun heteroxenous DR. WALID DARWICHE 40 40 Dr. Walid Darwiche 20 2022-2023 D. GENERAL TRENDS IN CYCLES 1. For ectoparasites Most often, monoxenous cycle No particular shape in the external environment (eggs, larvae, nymphs) Active infestation DR. WALID DARWICHE 41 41 2. For mesoparasites a. Protozoa case Monoxenous or heteroxenous cycle Forms of resistance in the external environment (eggs, oocysts, encysted larvae) Infestation by ingestion Example : the cycle of Eimeria tenella, the cecal coccidia of the hen. This parasite has a monoxenous cycle (the hen is the only host). It is an intracellular parasite of the enterocytes which will cause the tearing of the intestinal cells when it leaves the host, creating diarrhea in the infested hen. DR. WALID DARWICHE 42 42 Dr. Walid Darwiche 21 2022-2023 Another example : Toxoplasma gondii, with a dixenous cycle Prepatent period = (Ppp) = time interval between contamination of the definitive host by an infesting form and the release of eggs, larvae or ovigerous segments of the adult parasite. It is very important to know the prepatent period in order to know from how long after the infestation the animal will show symptoms and to know after how long the environment will be reinfested. Examples : Eimeria tenella : Ppp = 7 days Fasciola hepatica : PPP = 3 months DR. WALID DARWICHE 43 43 b. Case of metazoans (helminths, taenias, ascaris) Often heteroxene cycle (sometimes monoxene) Intermediate host in the food chain of the definitive host Example 1 : Taenia taeniaeformis cycle, cat's cestode DR. WALID DARWICHE 44 44 Dr. Walid Darwiche 22 2022-2023 Example 2: cycle of Dicrocoelium lanceolatum, the small fluke In the morning, the ant comes out of the anthill and climbs to the top of a blade of grass. The temperature rises, when it exceeds 10 ° C, the mandibles of the ant become paralyzed: it is stuck at the top of its blade of grass. DR. WALID DARWICHE 45 45 Example 3: cycle of Fasciola hepatica, the great fluke DR. WALID DARWICHE 46 46 Dr. Walid Darwiche 23 2022-2023 Example 4: cycle of Ostertagia ostertagi, the digestive strongyle of cattle ("very small, but very bad") The larvae live in the lining of the abomasum and all exit at the same time in the wall of the abomasum by tearing the cells: the abomasum of the cow is partially or even totally destroyed. DR. WALID DARWICHE 47 47 3. For endoparasites Heteroxenous cycle Case of protozoa and metazoa Examples: Leishmania infantum, endoparasite of dogs and humans (responsible for leishmaniasis), the vector of which is a phlebotom DR. WALID DARWICHE 48 48 Dr. Walid Darwiche 24 2022-2023 DR. WALID DARWICHE 49 49 Cycle of Dirofilaria immitis, the dog's heartworm Microfilariae are small larvae found in the blood of dogs. This disease is only found in areas with mosquitoes. It is therefore sometimes necessary to make a real investigation to succeed in associating clinical signs of heart failure with the presence of a worm. DR. WALID DARWICHE 50 50 Dr. Walid Darwiche 25 2022-2023 fina bas nehfaz l summary w hodik netkhattahun Summary:  General trends: Ectoparasites: monoxenous often (not always) Mesoparasites  Protozoa -) monoxenous  Metazoa → often heteroxenic → sometimes monoxenous Endoparasites: heteroxenous  Life cycles are necessary for a good understanding of the clinical expression of parasitic diseases.  The epidemiology is the study of diseases and health factors across a population. DR. WALID DARWICHE 51 51 DR. WALID DARWICHE 52 52 Dr. Walid Darwiche 26