Vector-Borne Zoonoses

Vector-Borne Zoonoses - Buzzing Bad Guys

• Definition: Infections naturally transmitted between vertebrate animals and humans, facilitated by arthropod vectors (e.g., mosquitoes, ticks, fleas, sandflies).
• Pathogen Spectrum: Viruses (Dengue, JE, KFD), Bacteria (Plague, Rickettsioses, Tularemia), Protozoa (Leishmaniasis, Babesiosis).
• Vector Control: Integrated strategies including source reduction, chemical (insecticides), biological (predators), and personal protection.

⭐ Transovarial transmission (pathogen from adult female to eggs, e.g., KFD virus in ticks) and transstadial transmission (pathogen retained through vector molts) ensure persistent endemicity and are crucial for some diseases' ecology in India.

Vector-Borne Zoonoses - Arboviral Villains

Arboviruses (arthropod-borne viruses) are a major cause of vector-borne zoonoses in India. Key diseases include:

⭐ KFD often presents with a biphasic illness: an initial phase of fever and myalgia, followed by a remission, and then a second phase characterized by neurological or hemorrhagic manifestations in some patients.

📌 DENgue: DENse pain (bone-break fever). CHIkungunya: CHIckens can't walk (severe arthralgia).

Vector-Borne Zoonoses - Rickettsial Terrors

• Scrub Typhus (Orientia tsutsugamushi)

  • Vector: Mite larvae (chiggers, Leptotrombidium)
  • Reservoir: Rodents
  • Clinical: High fever, headache, myalgia, maculopapular rash, eschar (painless, black necrotic lesion) at chigger bite site.
  • 
  • Diagnosis: Weil-Felix (OX-K positive), serology (IFA), PCR.
  • Treatment: Doxycycline.

• Indian Tick Typhus (Rickettsia conorii; Boutonneuse Fever)

  • Vector: Ticks (e.g., Rhipicephalus sanguineus)
  • Reservoir: Rodents, dogs.
  • Clinical: Abrupt fever, headache, rash (maculopapular, often on palms/soles), eschar ("tache noire") at tick bite site.
  • Diagnosis: Weil-Felix (OX-19, OX-2 positive), serology (IFA), PCR.
  • Treatment: Doxycycline.

⭐ Weil-Felix Test Pattern:

• Scrub Typhus (O. tsutsugamushi): Agglutinates Proteus OX-K.
• Indian Tick Typhus (R. conorii): Agglutinates Proteus OX-19 & OX-2.

Vector-Borne Zoonoses - Fleas, Flies & Fiends

• Plague (Yersinia pestis)

  • Agent: Gram-neg coccobacillus (bipolar "safety-pin" stain).
  • Vector: Fleas (X. cheopis); Reservoir: Rodents.
  • Clinical: Bubonic (tender buboes), septicemic, pneumonic (highly fatal).
  • Dx: Microscopy (Wayson/Giemsa), culture.
  • Rx: Streptomycin, Gentamicin, Doxycycline.

• Kala-azar (Visceral Leishmaniasis - L. donovani)

  • Agent: Intracellular protozoan.
  • Vector: Sandfly (P. argentipes); Reservoir: Humans (India).
  • Clinical: Chronic fever, massive splenomegaly, hepatomegaly, weight loss, pancytopenia. PKDL.
  • Dx: LD bodies in Giemsa-stained aspirates (bone marrow/spleen), rK39 test.
  • Rx: Liposomal Amphotericin B (DOC), Miltefosine.

  ⭐ Kala-azar diagnostic triad: Prolonged fever (>2 weeks), marked splenomegaly, weight loss.

High‑Yield Points - ⚡ Biggest Takeaways

• Kyasanur Forest Disease (KFD): Tick-borne Flavivirus; hemorrhagic fever; Karnataka; Haemaphysalis tick.
• Japanese Encephalitis (JE): Mosquito-borne Flavivirus (Culex); pigs amplify; encephalitis.
• Scrub Typhus: Orientia tsutsugamushi; mite-borne (chiggers); eschar is key; treat with doxycycline.
• Plague: Yersinia pestis; flea-borne (rodents); bubonic (painful nodes), pneumonic, septicemic forms.
• Leishmaniasis (Kala-azar): Leishmania donovani; sandfly-borne; splenomegaly, pancytopenia, fever.
• Dengue Fever: Mosquito-borne Flavivirus (Aedes); breakbone fever; risk of DHF/DSS.
• Chikungunya Fever: Mosquito-borne Alphavirus (Aedes); severe, debilitating arthralgia.