1. P ARASITOLOGY Dr. Md Fazlul Haque Assistant Professor Dept. of Zoology Rajshahi University

2. What is Parasitology?  Parasitology is the branch of Science which mainly deals about all the Parasites and its infectious diseases. What is parasite?  A parasite is a living organism, which takes its nourishment and other needs from a host; the host is an organism which supports the parasite. Thus, parasites get benefits at the expense of the host.  Parasite, from the Latin parasitus,(the Greek parasitos ), “one who eats at the table of another”  Traditionally parasite referred primarily to organisms visible to the naked eye, such as helminths. But, now Parasite includes microscopic organisms such as protozoa, viruses, and bacteria.

3.  How is a parasite differ from a predator?  Unlike predators, parasites typically do not kill their host, are generally much smaller than their host, and will often live in or on their host for an extended period. Parasites show a high degree of specialization, and reproduce at a faster rate than their hosts.  Parasites usually take resources from one host, whereas predators eat many prey.

4.  How is a parasite differ from a parasitoid?  A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism, and ultimately kills the host.  Thus in a typical parasitic relationship, the parasite and host live side by side without lethal damage to the host.  Typically, the parasite takes enough nutrients to thrive without preventing the host from reproducing. In a parasitoid relationship, the host is killed, normally before it can produce offspring. Female Apocephalus borealis ovipositing eggs into the abdomen of a worker honey bee

5. Is parasite a member of Symbiosis?  Symbiosis means “living together of both members of two different species.  Any organism that spends a portion or all its life intimately associated with another living organism of a different species is known as a symbiont (or symbiote), and the relationship is designated as symbiosis.  The term symbiosis is used in its original sense (living together) without any reference to “benefit” or “damage” to the symbionts.  There are at least three categories of symbiosis whose are commonly recognized: 1. Parasitism (+ / -) 2. Mutualism (+ / +) 3. Commensalisms (+ / )

6. Parasitism?  Parasitism is a type of symbiotic relationship between two organisms: a parasite, usually the smaller of the two, and a host, upon which the parasite is physiologically dependent.  The relationship may be permanent, as in the case of tapeworms found in the vertebrate intestine, or temporary, as with female mosquitoes, some leeches, and ticks, which feed intermittently on host blood.  In other words, it is a symbiotic relationship in which one animal (the host) is to be injured by the activities of the other animal (the parasite) to be benefited.

7. Commensalism?  Commensalism was derived from Latin for “eating at same table”, denotes an association which is beneficial to one partner and at least not disadvantageous to the other.  The two partners can survive independently.  Humans harbor several species of commensal protozoans, that colonize in the intestinal tract such as Entamoeba dispar, Entamoeba hartmanni, Endolimax nana Mutualism?  Mutualism is an association in which the mutualist and the host depend on each other physiologically.  It is seen where such associations are beneficial to both organisms(partners).  At least 20% of insect species, as well as many mites, spiders, crustaceans, and nematodes, are mutually infected with bacteria of genus Wolbachia.

8. T YPES OF PARASITES Depending on size: 1. Macroparasites : parasites which are visible to the naked eye, such as helminthes, tick, mosquitos etc. 2. Microparasites : Parasite which are typically smaller or microscopic in size, such as protozoa, viruses, and bacteria.

9. T YPES OF PARASITES Depending on living place on host: 1. Ectoparasite – The parasitic organism that lives on the outer surface of its host, e.g. lice, ticks, mites etc. 2. Endoparasite – The parasites that live inside the body of their host, e.g. Entamoeba histolytica, Taenia solium etc. Endoparasites can exist in one of two forms: a) Intercellular parasites: The parasites that are inhabiting spaces in the host’s body b) Intracellular parasites The parasites that are inhabiting in cells in the host’s body. Intracellular parasites, such as protozoa, bacteria or viruses, tend to rely on a third organism, which is generally known as the carrier or vector.

10. T YPES OF PARASITES 3. 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.

11. T YPES OF PARASITES Based on their interactions with their hosts and on their life cycles: Obligate Parasite - This parasite is completely dependent on the host during a segment or all of its life cycle, e.g. Plasmodium sp. Facultative parasite: An organism that exhibits both parasitic and non-parasitic modes of living and hence does not absolutely depend on the parasitic way of life, but is capable of adapting to it if placed on a host. E.g. Naegleria fowleri. Temporary (intermittent) parasites – A parasite such as mosquitos that are parasitic for limited periods for either feeding or reproduction. Permanent parasite: A parasite, such as a fluke or an itch mite, that lives on its host until maturity or spends its entire life on its host.

12. T YPES OF PARASITES Accidental parasite – when a parasite attacks an unnatural host and survives. e.g. Hymenolepis diminuta (rat tapeworm) is a cestode of rodents infrequently seen in humans. Erratic parasite - is one that wanders in to an organ in which it is not usually found. e.g. Entamoeba histolytica in the liver or lung of humans. Epiparasite: An epiparasite is one that feeds on another parasite. This relationship is also sometimes referred to as hyperparasitism, exemplified by a protozoan (the hyperparasite) living in the digestive tract of a flea living on a dog.

13. T YPES OF PARASITES  Social parasites: They take advantage of interactions between members of social organisms such as ants or termites. It may be two types: Interspecific social parasitism and Intraspecific social parasitism.  An example of interspecific social parasitism is Phengaris arion, a butterfly whose larvae employ mimicry to parasitize certain species of ants.  An example of Intraspecific social parasitism this is parasitic nursing, where some individuals take milk from unrelated females. In wedge-capped capuchins, higher ranking females sometimes take milk from low ranking females without any reciprocation. The high ranking females benefit at the expense of the low ranking females.

14. T YPES OF PARASITES  Brood Parasite: Brood parasites are organisms that rely on others (the host) to raise their young. An example is the brood parasitism practiced by cuckoos and cowbirds, which do not build nests of their own and leave their eggs in nests of other species.  The host behaves as a "babysitter" as they raise the young as their own.  Kleptoparasitism: Kleptoparasitism (parasitism by theft) is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food

15. T YPES OF PARASITES Adelpho-parasite: An adelpho-parasite (from the Greek αδελφός (adelphos), brother) is a parasite in which the host species is closely related to the parasite, often being a member of the same family or genus. An example of this is the citrus blackfly parasitoid, Encarsia perplexa, unmated females of which may lay haploid eggs in the fully developed larvae of their own species. These result in the production of male offspring. Monogenic parasites: Monogenic parasites complete the whole life cycle in one host, such as with Entamoeba histolytica. Digenetic parasite: A digenetic parasite needs, in addition to a primary host, also a secondary host to complete the entire life cycle. Plasmodium vivax (malaria parasite) completes its asexual part of life cycle in people and the sexual part in the female Anopheles mosquito.

16. H OST What is host? Host is defined as an organism which-  harbours the parasite and provides the nourishment and shelter.  are relatively larger in size and longer in lifetime in comparison to their parasites.  are not directly killed by parasites. What is carrier? Carrier is an individual (not all member of species/group) who harbours -  parasite without any clinical symptoms of disease, and  can acts as an important source of infection to other individuals in epidemiology

17. T YPES OF H OST Hosts are classified according to their role in the life cycle of the parasite into following types: Definitive host  The host that harbours the adult or sexually mature stages of the parasite is called definitive host  or the host in whom sexual reproduction occurs is called definitive host  e.g. man is definitive host for Schistosoma haematobium (Blood fluke),  e.g. female Anopheles mosquito is definitive host for Plasmodium species (malaria parasites).

18. T YPES OF H OST Intermediate host  The host that harbours larval or sexually immature stages of the parasite is called intermediate host  or the host in whom asexual reproduction occurs is called intermediate host  e.g. Man is intermediate host of malaria parasites.  e.g. Two intermediate hosts termed 1st and 2nd intermediate host may be needed for completion of a parasite's life cycle, e.g. Pirenella conica snail is the 1st intermediate host, while Tilapia fish is the 2nd intermediate host for Heterophyes heterophyes (small parasitic fluke).

19. T YPES OF H OST Reservoir host  The host (species/group) that makes the parasite available for the transmission to another host and is usually not affected by the infection (no clinical symptom).  It differs from a carrier which is an individual (not all member of species/group) who harbours parasite without clinical symptoms.  e.g. sheep are Reservoir host for Fasciola hepatica.

20. T YPES OF H OST Paratenic or transport host  The host in whom the parasite does not undergo any development but remains alive and infective to another host is called Paratenic or transport host.  Paratenic hosts fill the gap between the hosts.  For example, dogs and pigs may carry hookworm ( Ancylostoma duodenale ) eggs from one place to another, but the eggs do not hatch or pass through any development in these animals.  It differs from Vector which is an animal (usually arthropods) that transmits parasites from one host to another, e.g. female sand fly transmits Leishmania parasites.

21. T YPES OF H OST Typical or Natural host  A host that is naturally infected with certain species of parasite is called typical or natural host.  e.g. Rodents are natural host for Hymenolepis diminuta (rat tapeworm) Accidental host  A host that is under normal circumstances not infected with the parasite is called accidental host  Human is an accidental host for Hymenolepis diminuta (rat tapeworm)

22. H OST AS AN ENVIRONMENT OF PARASITE Environment:  The environment is the sum total of physical and biotic condition influencing the response of the organisms (S. C. Kendeigh, 1074)  The physical and biological conditions of host have both  positive (good) impact on life of parasite.  negative (bad) impact on life of parasite.

23. H OST AS AN ENVIRONMENT OF PARASITE Positive impact: Provide ready-made nourishment (degree of impact depend on availability of nutrients) Provide ready-made shelter Help in reproduction Protect from predator and mechanical injuries Protect from adverse effect of physical factors such as temperature, Ph, humidity, water activity, osmotic pressure Negative impact: Elimination or suppression by host immunity (Innate immunity and adaptive immunity) Elimination or suppression because of competition for nutrient and space

24. H OST PARASITE RELATIONSHIP Once the infecting organism is introduced into the body of the host, it reacts in different ways and this could result in: Carrier state  A perfect host parasite relationship where tissue destruction by a parasite is balanced with the host’s tissue repair.  At this point the parasite and the host live harmoniously, i.e. they are at equilibrium. Disease state  This is due to an imperfect host parasite relationship where the parasite dominates over the host.  It can result either from lower resistance of the host or a higher pathogenicity of the parasite. Parasite destruction  It occurs when the host dominates over the parasites.  It can result either from higher resistance of the host or a lower pathogenicity of the parasite.