Sex and behaviour: macroparasites & microparasites CfE Advanced Higher Biology Unit 2: Organisms and Evolution

SQA mandatory key area Macroparasites: endoparasitic amoebas, platyhelminths, nematodes. Ectoparasitic arthropods. Ectoparasitic Transmission through direct contact, consumption of secondary hosts or endoparasitic transmission by vectors. Schistosomiasis and malaria. Microparasites: viruses and bacteria. Human diseases: influenza, HIV/AIDS and tuberculosis. Viral structure and replication. Antigenicity. RNA retroviruses and reverse transcriptase.

Key concepts 1 Ectoparasites and endoparasites of the main body cavities, such as the gut, are generally transmitted by direct contact or through consumption of secondary hosts. Endoparasites of the body tissues are often transmitted by vectors. Schistosomiasis and malaria as examples of human diseases caused by a macroparasites.

Key concepts 2 Viruses are infectious agents that can only replicate inside a host cell. Viruses contain genetic material in the form of DNA or RNA, packaged in a protective protein coat. Some viruses have a lipid membrane surround derived from host cell materials. The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign. RNA retroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell. This virus gene forms new viral particles when transcribed.

Macroparasites vs microparasites The main distinction between microparasites and macroparasites is whether they “multiply” within their definitive host or not.   Microparasites do “multiply” in their definitive host, and macroparasites do not “multiply” in their definitive host.   This distinction is important because it influences the ecology and epidemiology of micro and macroparasitic infections.

Multiply vs reproduce Both microparasites and macroparasites may reproduce in the definitive host.   However, in macroparasites, reproduction usually leads to the production of eggs or larval stages that then leave the definitive host.  That is, reproduction occurs, but the host does not end up with more parasites.   Microparasites use direct reproduction; reproduction leads to an increase in the number of parasites within the host.

Macroparasite – endoparasite vs ectoparasite Parasites that live on the outside of the host, either on the skin or the outgrowths of the skin, are called ectoparasites. Your gut is actually, developmentally speaking, the outside of your body so the parasites that inhabit the gut can also be considered ectoparasites. Those that live inside the host are called endoparasites (including all parasitic worms). Endoparasites can exist in one of two forms:intercellular parasites (inhabiting spaces in the host’s body) or intracellular parasites (inhabiting cells in the host’s body).

Macroparasite example: Platyhelminth http://upload.wikimedia.org/wikipedia/commons/4/4d/Metagonimus_LifeCycle.gif

Macroparasite example: Schistosomiasis http://upload.wikimedia.org/wikipedia/commons/f/fb/Schistosomiasis_Life_Cycle.png

Vectors You will have noticed that the two previous examples are spread by a vector, an organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another. Which organism would be the vector in each case?

Microparasite A microparasite completes a full life cycle within one host and can be transmitted directly to conspecific hosts. They often reproduce within a host's cells and are generally too small to be seen with the naked eye. Most are viruses, bacteria and fungi with a smaller number being protists. Microparasite examples: viruses and bacteria. Human diseases: influenza, HIV/AIDS and tuberculosis.

How do viruses replicate? http://www.nature.com/nrmicro/journal/v1/n3/images/nrmicro775-i1.gif

Viruses can also replicate within bacteria – phage virus

Viruses Viruses are infectious agents that can only replicate inside a host cell. Viruses contain genetic material in the form of DNA or RNA, packaged in a protective protein coat. Some viruses have a lipid membrane surround derived from host cell materials. The outer surface of a virus contains antigens that a host cell may or may not be able to detect as foreign. RNA retroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell. This virus gene forms new viral particles when transcribed.

Macroparasites vs microparasites Move onto Activity H Macroparasites vs microparasites