ANTHROPODS

• Arthropods


  • Pairs of jointed appendages
  • Chitinized exoskeleton
  • Hemocele (blood-containing spaces)
• There are over four times as many species of arthropods as there are species in the remainder of the entire animal kingdom
• Arthropods are of particular interest to parasitologists because they are responsible for the transmission of parasites, bacteria, viruses, and rickettsial organisms, as well as directly causing disease in humans
• This student will be able to identify and differentiate the arthropods discussed in this chapter based on their key characteristics
• Ectoparasites


  Parasites established in or on the exterior of the body
• Laboratory diagnosis of arthropods

  1. Immerse in 70% ethanol as a preservative

  2. Inactivate flying insects with chloroform or ether before immersion in alcohol

  3. Place in 5% formalin or sterile saline solution

  4. Use Berlese's medium as a permanent method to kill and fix specimens

  5. Examine under microscope or dissecting microscope
• Arthropods may affect humans in various ways: take up residence as temporary or permanent occupants, cause disease themselves, transmit disease as mechanical transfer agents, be part of the parasite's life cycle, cause disease through living and growing in or on the skin or hair, or inject venom during a bite
• Patients who have been bitten by or infested with arthropods may exhibit symptoms related solely to the bite itself or the presence of these arthropods, and may also present with symptoms relating to the invasion of the specific pathogenic microorganism transferred by the arthropod to the human
• Topical lotions or ointments are available for the treatment of arthropod bites, and treatment of ectoparasite infestations requires the removal of the arthropod from the skin
• Complete eradication of arthropods is almost impossible, but control measures include the destruction of arthropod breeding grounds, increasing natural predators, and the use of protective clothing and arthropod repellents
• Vertical transmission occurs when an arthropod passes infective agents to its offspring
• Ticks

  • Four pairs of legs
  • Two pairs of mouthparts
  • No antennae
• Tick classification

  • Order Ixodida
  • Family Ixodidae (hard body)
  • Family Argasidae (soft body)
• Capitulum


  Umbrella term referring to the mouthparts of ticks and mites
• Ticks

  • Have four pairs of legs, two pairs of mouth parts, and no antennae
  • Are of the order Ixodida, which contains the family Ixodidae (hard body) and the family Argasidae (soft body) ticks
  • Are somewhat oval in shape
  • Have the head, thorax, and abdominal regions meshed together and appear as a single structure
  • Have four pairs of legs and lack antennae and a head region
  • Have separate sexes
• Hard ticks


  Have a visible capitulum on the dorsal side, a dorsal hard shield known as a scutum, and range in size from 6 to 8 mm long
• Soft ticks

  Have the capitulum on the ventral side, a leathery outer surface, and lack the scutum
• Tick life cycle

  1. Eggs

  2. Larvae (juvenile stage)

  3. Nymphs (developmental stage resembling adult)

  4. Adults of separate sexes
• Tick life cycle ranges from 1 to 2 years, depending on the hatch season
• Ticks can pass many microorganisms to their offspring, resulting in a renewable source of the infectious agent
• Tick life cycle process

  1. Eggs hatch on the ground

  2. Motile larvae emerge and migrate to sites like blades of grass and twigs

  3. Larvae jump onto the first viable host, feed via a blood meal, fall off the host and back to the ground, and molt into nymphs

  4. Nymphs migrate to potential host-passing sites, attach to a second host, repeat the larval process, then molt and transform into adult ticks

  5. Adult hard ticks only feed once, while adult soft ticks feed repeatedly

  6. After mating, eggs are deposited on the ground and the cycle repeats
• Ticks complete a blood meal by making a cut into the host epidermis using a toothed structure near their mouth called a hypostome
• The blood obtained during the tick feeding process does not clot due to the presence of an anticoagulant in the tick's salivary gland
• As the tick feeds, its body expands
• Tick-borne diseases

  • Bacterial
  • Viral
  • Rickettsial
• Hard ticks such as Ixodes spp. (deer ticks) have a wide geographic range covering most of North America and are the primary vector for Borrelia burgdorferi (Lyme disease) and Babesia spp.
• Dermacentor spp. (dog ticks) can be found from the eastern United States to the Rocky Mountain range and are associated with a number of rickettsial diseases, including Rocky Mountain spotted fever
• Amblyomma americanum (lone star tick) can be found in the southern states east of the Rocky Mountains and is the vector for human ehrlichiosis
• Soft ticks of the genus Ornithodorus are primarily responsible for transmitting Borrelia spp., which causes relapsing fever
• Different species of Ornithodorus are found in different geographic ranges within the United States and Canada
• Patients infected with ticks often exhibit skin reactions to the bite site, including inflammatory infiltration of tissues, edema, local hyperemia, and hemorrhage
• Tick paralysis may occur when the salivary secretions of certain tick species (Dermacentor) are introduced into the host, resulting in toxemia and potentially death if the tick is not removed
• Recommended therapy for tick infestation

  Remove the tick by placing a few drops of ether or chloroform on the head and pulling the tick straight out, ensuring the entire tick is removed
• Mouth parts left behind may be the source of severe tissue reactions and secondary infection
• Total tick eradication is difficult, but measures like avoiding tick-infested areas, wearing protective clothing, using tick repellents, and promptly removing ticks can help decrease the chance of infection
• A prophylactic vaccination has been developed to help protect individuals from deadly rickettsial infections transmitted by ticks
• Transfer of infectious agents from tick bites may take hours to days, so ticks should be removed as soon as possible to interfere with disease transfer
• Mites


  Extremely small (0.1-0.4 mm) but visible to the naked eye, oval in shape
• Mite life cycle

  1. Adult mites burrow into the skin, hair follicles, or sebaceous glands of hosts and lay eggs

  2. Eggs hatch and mature from larval through nymph stage to adult forms, all within the tunnels made by the original adult mite

  3. Newly developed mites can begin new burrows and continue the spread of the infestation

  4. The life cycle takes approximately 2 weeks from egg to adult stage
• Transfer of mites from one person to another usually requires prolonged close contact, but may also spread rapidly in overcrowded conditions