Ectop human

• Phylum Arthropoda includes groups of human relevance such as Crustacea (Pentastomida - Linguatula, tongueworm) and Chelicerata (Arachnida)
• Crustacea / Pentastomida:

  • Linguatula serrata, tongueworm, can cause accidental infection in humans (visceral linguatuliasis)
  • Rarely causes nasopharyngeal linguatuliasis
  • Nymphs can cause lymphatic obstruction, pericarditis, icterus, and brain/ocular damage
• Chelicerata - Arachnida - Acari:

  • Incomplete metamorphosis
  • Ticks are obligate parasites, while mites can be both parasitic and free-living
  • Ticks can act as vectors, mites can cause skin damage and allergies
• Acari (Parasitiformes, Ixodida) - Hard ticks (Ixodidae):

  • Nymphs are the most common stages found on humans
  • Various modes of transmission including feeding, cutaneous, co-feeding, trans-stadial, and trans-ovarial
  • Ixodes ricinus is the main vector for Borrelia spirochetes and other pathogens
• Acari (Parasitiformes, Ixodida) - Soft ticks (Argasidae):

  • Short feeding time, usually during the night
  • Allergic reactions at the biting site can occur
  • Vectors for tick-borne relapsing fever
• Acari (Parasitiformes, Mesostigmata) - Mites I Families:

  • Dermanyssidae (Dermanyssus gallinae) and Ornithonyssidae (Ornithonyssus sp.)
  • Can bite humans and cause dermatitis, with a low risk of rickettsial transmission
• Ectoparasites: Sarcoptes scabiei v. hominis:

  • Small mites with females surviving up to 2 months
  • Short survival off the host (3-4 days)
• Ectoparasites: Sarcoptes scabiei life cycle
• Ectoparasites: scabies' clinical relevance:

  • Initial infection may involve 50-500 mites, decreasing to about 20 in chronic infections
  • Symptoms include itching, papular dermatitis, and potential secondary bacterial infections
• Ectoparasites: scabies - diagnosis:

  • Skin scraping for direct diagnosis
  • Microscopic examination of mites and eggs/eggshells
• Ectoparasites: scabies - treatment:

  • Permethrin cream, crotamiton, sulfur ointment, lindane lotion, or ivermectin depending on the severity
  • Crusted scabies may require oral and topical treatments
• Ectoparasites: follicular dermatitis:

  • Demodex folliculorum and Demodex brevis can cause dermatitis
  • Clinical signs include red skin, papulopustular rosacea, and blepharitis
• Ectoparasites: chiggers and dust mites:

  • Chiggers cause skin irritation from larval saliva, while dust mites can lead to respiratory allergies
  • House dust mites like Dermatophagoides pteronyssus are major allergens
• Respiratory allergy affects 5-7% of the population
• Major allergens from Dermatophagoides pteronyssus include Der p I in faeces and Der p II in the body
• Major allergens from Dermatophagoides farinae include Der f I and Der f II
• Sensitization to 2 μg/g dust can occur, with allergic reactions in sensitive individuals at 10 μg/g dust
• Lower humidity and acaricides like benzyl benzoate can help with environmental sanitation in the bedroom
• Hexapoda (Insecta) have complete (dipterans, fleas) or incomplete metamorphosis (lice, bedbugs)
• There is a large variation in the degree of parasitism based on species and developmental stages
• Ectoparasites can cause damage as vectors (mosquitoes), skin damage (lice, fleas), and dipteran larvae feeding on living tissues (myiasis)
• Lice belong to the clade Phtiraptera, superfamily Anoplura, with 3 species: Pediculus humanus capitis (head louse), Pediculus humanus humanus (body louse), and Pthirus pubis (crab/pubic louse)
• They are flattened insects (2-4mm, nits 1mm) and are obligate, permanent parasites
• Transmission of lice occurs via direct contact, including healthy carriers
• Head lice can cause itching (14%-36%), maculopapular rash, allergy to lice saliva, enlarged cervical lymph nodes, and secondary infections on damaged skin
• Body lice can cause itching, allergy to lice saliva (with fever, headache, fatigue), hyperpigmentation, enlarged lymph nodes, and can act as vectors for diseases like epidemic typhus, trench fever, and relapsing fever
• Pubic lice infest pubic hair, armpits, eyebrows, and rarely other hair, causing itching, blue skin staining (maculae caeruleae), and red staining of underwear from louse feces
• Diagnosis for all lice species is direct on hair (head/pubic lice) or textiles (body lice), with treatments including OTC options like pyrethrins, permethrin lotion 1%, prescription medications, and second-line treatments like Lindane shampoo 1%
• Fleas (Siphonaptera) undergo complete metamorphosis and can transmit diseases like plague, murine typhus, flea-borne spotted fever, cat-scratch disease, and tapeworms
• Management and control of fleas involve sanitation, pet treatment, home treatment, and follow-up
• Bedbugs (Cimex lectularius, C. hemipterus, C. pipistrelli) are hematophagous insects causing skin irritation and reactions to saliva, with treatment options like pyrethroids and carbamates
• Myiasis is an infection with fly larvae, with different types like furuncular, nasopharyngeal, genital, migratory, ophtalmomyiasis, and wound myiasis caused by various fly species
• Insects like mosquitoes, sandflies, blackflies, Glossina spp., and reduviid bugs can act as vectors for diseases like West Nile virus, Plasmodium spp., Leishmania spp., Trypanosoma spp., and others
• Ectoparasites in humans can lead to skin diseases, vectorial capacity for disease transmission, allergies, and delusional parasitosis