Arthropod Vectors - The Unwanted Guests
- Mosquitoes: Transmit key viral & parasitic diseases.
- Anopheles: Malaria
- Aedes: Dengue, Chikungunya, Zika, Yellow Fever
- Culex: West Nile Virus, St. Louis Encephalitis
- Ticks: Arachnids carrying bacterial & protozoal pathogens.
- Ixodes scapularis: Lyme disease, Anaplasmosis, Babesiosis. 📌 Remember L.A.B. (Lyme, Anaplasmosis, Babesiosis).
- Dermacentor: Rocky Mountain Spotted Fever (RMSF).
- Other Vectors:
- Louse: Epidemic typhus (R. prowazekii)
- Flea: Plague (Y. pestis)
- Tsetse fly: African Trypanosomiasis
- Sandfly: Leishmaniasis
- Reduviid bug: Chagas disease (T. cruzi)
⭐ The Ixodes tick can co-transmit Lyme disease, Anaplasmosis, and Babesiosis. Suspect co-infection with atypical presentations or severe illness.
Tick-Borne Diseases - A Walk in the Woods
- Vector: Primarily Ixodes scapularis (deer tick) in Northeast US; Dermacentor for RMSF; Amblyomma for Ehrlichiosis.
| Disease | Pathogen | Key Features | Treatment |
|---|---|---|---|
| Lyme Disease | Borrelia burgdorferi | Erythema migrans (bull's-eye rash), AV block, Bell's palsy | Doxycycline |
| Babesiosis | Babesia microti | Hemolytic anemia, jaundice, fever. "Maltese cross" tetrads. | Atovaquone + Azithromycin |
| Anaplasmosis | Anaplasma | Flu-like, thrombocytopenia, leukopenia. Morulae in granulocytes. | Doxycycline |
| Ehrlichiosis | Ehrlichia | Flu-like, thrombocytopenia, leukopenia. Morulae in monocytes. | Doxycycline |
| RMSF | Rickettsia rickettsii | Rash on palms/soles, spreading centrally. | Doxycycline |
📌 Lyme mnemonic: "B.A.K.E. a Key Lyme Pie" - Bell's palsy, Arthritis, Kardiac block, Erythema migrans.
Mites & Lice - The Itchy & Scratchy Show
-
Scabies (Sarcoptes scabiei)
- Intense pruritus (worse at night) from Type IV hypersensitivity. Burrows in interdigital spaces, wrists, axillae.
- Transmission: Prolonged skin-to-skin contact.
- Rx: Permethrin 5% cream (entire body, neck down), oral ivermectin. Treat all household members.
- 📌 Itching so bad you want to 'Scab-ies' your eyes out!
-
Lice (Pediculosis)
- P. humanus capitis (head), P. humanus corporis (body), Pthirus pubis (pubic).
- Nits (eggs) attached to hair shafts; pruritus from saliva.
- Rx: Topical permethrin, pyrethrins, malathion.
⭐ Body lice (Pediculus humanus corporis) are vectors for diseases like epidemic typhus (Rickettsia prowazekii) and trench fever (Bartonella quintana).
Other Vectors - Fleas, Flies, & Foes
- Flea (Xenopsylla cheopis)
- Yersinia pestis (Plague): Gram-negative rod causing buboes (painful lymph nodes), fever, and sepsis. 📌 Classic "safety-pin" bipolar staining.
- Rx: Streptomycin or gentamicin.
- Sandfly
- Leishmania spp.: Intracellular protozoa. Presents as cutaneous (ulcers) or visceral disease (kala-azar: fever, hepatosplenomegaly, pancytopenia).
- Dx: Amastigotes in macrophages.
- Other Flies
- Tsetse Fly → Trypanosoma brucei (African sleeping sickness)
- Deer Fly → Loa loa (Loiasis)
⭐ Plague: Yersinia pestis can be transmitted via flea bites, aerosols (pneumonic), or direct contact. Its high mortality and potential for aerosol spread make it a major bioterrorism agent.
High‑Yield Points - ⚡ Biggest Takeaways
- Scabies (Sarcoptes scabiei) causes intensely pruritic burrows, especially in finger webspaces; treat with permethrin.
- Ixodes ticks are the vector for Lyme disease (Borrelia), Babesiosis, and Anaplasmosis.
- Dermacentor ticks transmit Rocky Mountain Spotted Fever (Rickettsia rickettsii).
- Chagas disease (Trypanosoma cruzi), from the Reduviid bug, classically causes cardiomyopathy and megacolon.
- Malaria (Plasmodium) is transmitted by Anopheles mosquitoes; Leishmaniasis is from sandflies.
- Aedes mosquitoes transmit key arboviruses like Dengue, Chikungunya, and Zika.
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