محاضرة رابعة

• Host-Parasite Relationship


  The relationship between the host and the parasite and the competition for supremacy that takes place between them
• Disease should not be confused with infection; a person may be infected without becoming diseased
• If the host has upper hand, due to increased host resistance


  It remains healthy and the parasite is either driven away or assumes a benign relationship with the host
• If the host loses the competition

  A disease develops
• Symbiosis


  Life together, the two organisms live in an association with one another
• Types of Symbiotic Association


  • Mutualism
  • Commensalism
  • Parasitism
• Mutualism


  A relationship in which both partners benefit from the association
• Mutualism is usually obligatory since in most cases physiological dependence has evolved to such a degree that one mutual cannot survive without the other
• Examples of Mutualism


  • Blood-sucking leeches and intestinal bacterial species
  • At least 20% of insect species, as well as many mites, spiders, crustaceans, and nematodes, are mutually infected with bacteria of genus Wolbachia
  • Filarial nematodes such Wuchereria bancrofti and Onchocerca volvulus and Wolbachia