parasites

• Endoparasites live inside the host organism.
• Ectoparasites are external to the body surface, but may be attached or embedded within tissues (e.g., flea larvae).
• Parasitic worms have complex life cycles involving multiple hosts.
• parasitism is the relationship between two organisms where one (the parasite) benefits at the expense of another (the host)
• A species has a fundamental niche that it occupies in the absence of any interspecific competition
• A realised niche is occupied in response to interspecific competition
• As a result of interspecific competition, competitive exclusion can occur, where the niches of two species are so similar that one declines to local extinction
• The human disease malaria is caused by Plasmodium


  An infected mosquito, acting as a vector, bites a human. Plasmodium enters the human bloodstream. Asexual reproduction occurs in the liver and then in the red blood cells. When the red blood cells burst gametocytes are released into the bloodstream. Another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to now occur. The mosquito can then infect another human host.
• Schistosomes cause the human disease schistosomiasis

  Schistosomes reproduce sexually in the human intestine. The fertilised eggs pass out via faeces into water where they develop into larvae. The larvae then infect water snails, where asexual reproduction occurs. This produces another type of motile larvae, which escape the snail and penetrate the skin of a human, entering the bloodstream.
• Viruses are parasites 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 are surrounded by a phospholipid membrane 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
• Viral life cycle stages: infection of host cell with genetic material, host cell enzymes replicate viral genome, transcription of viral genes and translation of viral proteins, assembly and release of new viral particles
• RNA retroviruses use the enzyme reverse transcriptase to form DNA, which is then inserted into the genome of the host cell
• Viral genes can then be expressed to form new viral particles
• Virulence is the harm caused to a host species by a parasite
• Ectoparasites are generally transmitted through direct contact
• Endoparasites of the body tissues are often transmitted by vectors or by consumption of intermediate hosts
• • Factors that increase transmission rates:
  • the overcrowding of hosts when they are at high density mechanisms, such as vectors and waterborne dispersal stages, that allow the parasite to spread even if infected hosts are incapacitated
• The host behaviour becomes part of the extended phenotype of the parasite