Parasites

• Parasites


  Eukaryotic organisms that infect different areas of the body, generally the blood and intestines
• Parasites


  • Parasitic symbiosis is where one member benefits and the other is harmed
  • Parasites that derive benefits from host without causing harm are called commensals, i.e. they don't cause infection, but they're still parasites
• Types of parasites


  • Protozoa
  • Helminths
  • Arthropods
• Protozoa


  • Most parasites are protozoa and parasitic protozoa are usually 50μm
  • Unicellular eukaryotes
  • Nucleus has a membrane, but unlike fungi and bacteria, they lack a cell wall
  • Protozoa can twist and bend
• Life Cycle of Protozoa


  1. Trophozoite: The active feeding and multiplying stage

  2. Oocysts: The stages resulting from sexual reproduction; this stage characterised with a protective membrane or thickened wall around parasite
• Reproduction of Protozoa


  • May be sexual or asexual or both
  • Asexual reproduction is achieved through binary fission
  • Sexual cycle involves: Production of gametes, Fertilization to form zygote, Encystation of zygote to form oocyst, Formation of infective sporozoites within the matured oocyst
• Nutrition of Protozoa


  • Protozoa are holozoic, meaning they require organic materials and can engulf particulate food
  • Many protozoa have a permanent mouth
  • Pinocytosis often occurs to draw in fluid from external environment, and this water sometimes has tiny material that'll help the parasite to digest and obtain nutrients
  • Vacuoles in the protozoa will perform digestion and they have enzymes, which help to break down the organic material
  • Metabolic pathway is similar to higher animals
• Examples of Protozoa Infections


  • Entamoeba histolytica - anaerobic parasitic protozoal commensal
  • Malaria - caused by protozoal sporozoa

  
• Malaria Life Cycle


  1. Mosquito injects sporozoites present in saliva of insect when they bite a person

  2. Sporozoites circulate in blood for a short time and then settle in parenchymal cells in liver and multiply, infecting the cells — this stage is known as pre-erythrocytic schizogony

  3. After 12 days, the Parenchymal cells rupture due to the merozoites, releasing 1000's of merozoites into the blood to infect red blood cells (RBCs)

  4. In RBCs, the parasites mature into trophozoites, which then transform to form daughter merozoites

  5. Some of the merozoites transform into male and female gametocytes

  6. Gametocytes will separate in the blood, waiting for another mosquito to bite the human and take it up

  7. The female gametocyte transforms into ookinete, is fertilized and forms an oocyst, which fuses inside the mosquito gut to produce sporozoites; this moves to the salivary glands and are ready to be injected into man when the mosquito next takes a meal

  
• Malaria Treatment


  • Treatment is effective with various quinine derivatives: Quinine sulfate, Choroquine, Mefloquine, Primaquine
  • Drug resistance is a major problem
  • Control measures include eradication of infected anopheline mosquitos, which would stop the disease
  • Preventative measure may also be used to prevent infection

  
• Types of Helminths


  • Flukes (trematodes)
  • Tapeworms (cestodes)
  • Roundworms (nematodes)
• Tapeworms (cestodes)


  • Generally flattened, elongated and consists of segments, proglottids
  • Vary in length, 2mm - 10m
  • Anatomically divided into: Scolex – head (used to attach themself to the human intestine, where they ingest the blood and consequently nutrients from the human), Neck – region of segment proliferation, Strobila – chain of proglottids
  • Characteristic feature is absence of alimentary canal
  • Substances enter the tapeworm across the tegument
  • Cestodes are hermaphroditic. Each proglottid possess male and female reproductive systems
  • Eggs are deposited in different methods according to the type of tapeworm
• Treatment of Tapeworm Infections


  • Praziquantel used to treat many Tenia infections
  • Expulsion of the scolex is a must
  • Must have good hygiene – especially regarding animals and children
• Ways Arthropods Affect Human Disease


  • Act as vectors
  • Acts as parasites
  • Illicit allergies

  
• Examples of Arthropod Parasites


  • Lice
  • Fleas
  • Mites
  • Ticks
• Lice


  • Affect three areas of the body: Head - Pediculus humanus capitis, Body - P. humanus humanus, Pubic region - Pthirus pubis
  • Lice tend to spend all of their life on one specific host and both male and female feed on blood
  • They only leave one host to transfer to another
• Head Lice


  • Symptoms include itching due to sensitization to louse saliva
  • Treatment: Shampoo containing 1% benzene hexachloride, Mixture of pyrentins 0.2% and pipronyl butoxide 2%, Brushing out