4.2 Species interactions -2

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1 Parasitism


Parasitism 2 One in which one organism, the parasite, lives off of another organism, the host, harming it and possibly causing death. Parasites promote biodiversity – help keep populations of hosts in check Both plants and animals can be parasites Parasites are smaller than hosts. Highly specialized for their mode of life Reproduce more quickly


Cleptoparasite . ‘A “thief” parasite, one that consumes the food stored by another insect in a nest. (Evans, 1984) Smaller or similar size as host; often closely related. Hyper/ Epiparasites . Parasite of a parasite. Usually smaller than host. Inquiline. “An organism that lives in the home of another, sharing food; in entomology, used particularly of residents in the nests of social insects or in plant galls induced by another organism.” (Gullen & Cranston 2005) Types of parasites A hyperparasitic  microsporidian , Nosema podocotyloidis , a parasite of a digenean ,  Podocotyloides magnatestis , which is itself a parasite of the fish Parapristipoma octolineatum   3


TYPES OF PARASITES 4 -Social Parasites- P arasites that take advantage of interactions between members of a social host species to their detriment Brood Parasitism

Parasites: 2 broad groups:

Parasites: 2 broad groups Microparasites Macroparasites 5 Multiplies within/ on the host Reproduction usually leads to the production of eggs or larval stages that then leave the definitive host. Tiny Short generation time Host can develop immunity Eg . Bacteria, virus, fungi , protozoa Grows in or on Use direct reproduction; reproduction leads to an increase in the number of parasites within the host.the host, but does not multiply. Large Long generation time No immunity against it Eg . Helminth worms, fleas, lice, ticks etc

Parasites: types:

Parasites: types 6 Parasitoids (or necrotrophs ) Use another organism’s tissue for their own nutritional benefit until the host dies from loss of needed tissues or nutrients Biotrophs Survives only on living tissue Wasps and flies Viruses

Parasites: types:

Parasites: types 7 Ectoparasites Parasites that lives outside the host’s body Endoparasites Parasites that lives inside the host’s body Mites Hookworm inside body

Modes of transmission:

Modes of transmission Horizontal Vertical 8 Among members of same population E.g. Measles, common cold (Direct) Malaria (Indirect) Passed from mother to offspring E.g. HIV, rubella

Plants as parasites:

Plants as parasites 9 have special organs, named haustoria (singular: haustorium), which connect them to the conductive system of their host and provide them with the ability to extract water and nutrient from the hosts Plant parasites: Mistletoe, Cuscuta

Plant as parasites:

Plant as parasites Hemiparasite Holoparasite 10 A plant that is parasitic under natural conditions and is also photosynthetic to some degree. Nuytsia floribunda (Western Australian Christmas tree) is an obligate root hemiparasite. Rhinanthus (e.g. Yellow rattle) is a facultative root hemiparasite. Mistletoe is an obligate stem hemiparasite. A plant that is completely parasitic on other plants and has virtually no chlorophyll. Dodder is a stem holoparasite. Hydnora spp. are root holoparasites.


Flea (SIPHONAPTERA) : adult only, intermittent, usually same host individual Diverse Parasite Relationships to Host Louse (PHTHIRAPTERA) : All stages, permanent on host Mosquito (DIPTERA) : adult only, intermittent, many host indiv’s Some Factors: Host specificity Duration on Host Life cycle dependency on Host Alternate hosts Number of host individuals


Kinds of Parasitism This parasite, called an “ eye worm ” comes from the bite of a deer fly. This eye worm can be crawling under one’s skin for years unbeknownst to them unless it reaches the eye. There, it will feel odd, and there will be a visible worm just beneath the eye surface. Usually found in India and Africa, the eye worm can cause itching, joint pain, and sometimes can be fatal.


Kinds of Parasitism This parasitic crustacean is called the “ tongue-eating louse ” for good reason. After entering the fish through the gills, and attaching itself to the tongue, it then starts to extract the fish’s blood via its front claws. This continues until the fish has wasted away due to lack of blood, after which, this parasite attaches its body to the muscles of the tongue. Thankfully, they can’t attack human’s this way. However, they do bite.


Kinds of Parasitism Also known as the “ Guinea worm” , this parasite gets into the body by drinking water contaminated with copepods (water fleas) which are infested with the larvae of the Guinea worm. A year or so after ingesting the contaminated water, a blister will appear, usually on the leg or foot. The blister ruptures 72 hours later, where an end of the worm will appear. These parasites are usually found in Asia and Africa, and can affect both humans and animals.


Kinds of Parasitism The sacculina controls the reproduction of its host by partially removing its “procreative organs” . The other option is killing the host. With female crabs, the parasite tricks it into carrying and spreading its larvae just as if it were its own larvae (baby crabs.) With male crabs, it tricks them into thinking they are females and transforms their bodies to function as that of a female.


Kinds of Parasitism Filarial worms are threadlike parasites that are transmitted from host to host usually by black flies and mosquitoes. These parasites can cause an edema called “elephantiasis”, an example of which is shown in the picture. They can also cause skin rashes, urticarial papules, and arthritis. They can also affect the eyes, causing onchocerciasis (river blindness), which is one of the main causes of blindness. This parasite can affect both humans and animals.


Kinds of Parasitism Dodder Plant Although this plant looks innocent enough, it is a parasite and lives off other plants. And, it doesn’t wait around either. This vine can sniff out its hosts and hunt them down. It can grow at a rapid pace and spread at an unbelievable rate, and is very hearty thanks to tough seeds. It can destroy crops if not caught early.


Kinds of Parasitism Botflies aren't easily confused with common houseflies - they're hairy and about twice as big. They lay their eggs on a mosquito, which then lands on a person. Once hatched, the larvae invade the skin of the unlucky host.

Parasite Life Cycle::

Parasite Life Cycle: 19 The life cycle is a never-ending chain of events that lead to the parasite constantly reproducing and re-infesting another animal. There are two types of lifecycles: Indirect - require different types of hosts or a vector (intermediate host) for various stages of their life cycle. Direct - a life cycle in which a parasite is transmitted directly from one host to the next without an intermediate host or vector of another species.


DIRECT LIFE CYCLE 20 Only humans are host Infective stage like ovum, cyst, larva passed out of body that infect healthy person Example E histolytica, Giardia, Ascaris lumbricoides .




INDIRECT LIFE CYCLE 22 Life cycle of Taenia saginata Multiple hosts or involvement of vector Definitive host, Intermediate host Example Taenia saginata spp , Schistosoma spp etc


ROLE OF VECTOR 23 Vector, a Latin word meaning " carrier“ Imp in transmission of parasite No direct damage by vector The Anopheles mosquito transmit Malaria, Filaria Sandfly is vectors for Leishmaniasis Domestic cats-vector of Toxoplasma gondii , Echinococcus granulosis

The Intermediate Host:

The Intermediate Host Required by some parasites to complete their life cycle, Advantages of an intermediate hosts include: increasing the spread of the parasite & protecting the parasite from spending too much time in the environment. 24


Meningeal worm infection. Snails carry the larvae. Deer accidentally eat the snails when grazing. Larva escape the snails, move into the blood stream, infect tissues surrounding the brain, eventually move into the lungs. The Intermediate Host


Liver Fluke Life Cycle 26

Importance of Life Cycles:

Importance of Life Cycles 27 Understanding the life cycle of a parasite provides valuable information concerning: The individual infested How the particular stage in the life cycle affects the host The most common time of year for the parasite to be in the environment Types of infestation/sickness caused by the organism Vulnerable points in the life cycle for the best treatment and prevention

Model of microparasite disease:

Model of microparasite disease 28 Basic reproductive rate: No. of new cases that arise from one infected host R p = ß s d 3 components Transmission rate –ß Number of susceptible hosts –S Duration of the infectious period –d Conclusions: R p < 1 Disease incidence is falling in the host popu . R p > 1 Disease incidence is rising in the host popu .

Regulation of parasite population:

Regulation of parasite population 29 Adaptation of hosts- Sickle-shaped anemia and malaria resistance Sterile male method- by wide spectrum antibiotics for mosquitoes, screwworms Differential susceptibility- Green frog and Candida humicola

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