Essence of the transmission mechanism and group specifics
The vector-borne mechanism involves the circulation of a pathogen in the bloodstream and its transfer to a susceptible organism by blood-sucking arthropods. It is important to distinguish true vector-borne transmission from other hematogenous routes: for example, HIV infection is transmitted parenterally and sexually, but is not spread through insect bites because the virus does not survive or replicate in their bodies.
Many pathogens of vector-borne diseases possess adaptive defense mechanisms—for instance, they form a capsule that shields bacterial antigens and hinders phagocytosis, thereby increasing the overall virulence of the microorganism.
Examples of vector-borne and polytropic infections
Among nosologies that utilize the vector-borne pathway (either in isolation or in combination with other mechanisms), the following are distinguished:
- Plague (causative agent — Yersinia pestis). Classified as a particularly dangerous infection (PDI). Characterized by lesions of the skin, lymph nodes, and respiratory tract, as well as the development of DIC syndrome and infectious-toxic shock. In addition to the vector-borne route, it is transmitted via contact, droplet/airborne, and alimentary routes.
- Tularemia (causative agent — Francisella tularensis). A natural focal zoonosis causing granulomatous inflammation of the lymph nodes, skin, and internal organs. It utilizes vector-borne, contact, alimentary, and aerosol transmission routes.
- Malaria (plasmodia Pl. falciparum, Pl. vivax, Pl. ovale, Pl. malariae). Characterized by involvement of the blood system, typical febrile paroxysms, and hepatosplenomegaly.
- Relapsing fever and hemorrhagic fevers — classic infections with hematogenous involvement.
Fundamentals of laboratory diagnostics
Diagnosis verification is based on the epidemiological history (visits to endemic areas) and a comprehensive examination:
- Parasitological and microscopic tests: examination of a thick blood film (to count parasites per 1 µl or per 100 microscope fields) and a thin blood smear (for precise identification of the pathogen species).
- Clinical and biochemical markers: complete blood count to detect anemia (hemoglobin, erythrocytes, platelets, ESR), blood biochemistry (bilirubin, transaminases, urea, creatinine, glucose), acid-base balance (ABB), and urinalysis.
- Instrumental methods: abdominal ultrasound to confirm organomegaly, chest X-ray, and ECG.
Principles of therapy and preventive measures
| Direction | Main measures and approaches |
|---|---|
| Treatment | Divided into suppressive (blood schizonticides) and radical (targeting tissue hypnozoites or gametocytes). |
| Hospitalization | In the Russian Federation, hospitalization in infectious diseases hospitals is mandatory; in endemic regions, it depends on the severity of the condition, and applies to children and pregnant women. |
| Vector protection | Use of repellents, bed nets, window screens, protective clothing, and disinsection. |
| Targeting the reservoir | Deratization measures in natural foci. |
| Medication-based prophylaxis | Prescription of chemoprophylaxis to non-immune individuals before traveling to high-risk areas. |
The three "D" rule in a focus: Disinsection (elimination of vectors) + Deratization (reservoir control) + Distance/defense (repellents, bed nets, chemoprophylaxis).
Class and exam questions
Why is HIV infection not classified as a vector-borne disease?
Blood-sucking insects cannot serve as vectors for HIV because this virus cannot remain viable and replicate within the arthropod organism.
What is the difference between a blood smear and a thick blood film in malaria diagnostics?
A thick film is used for the quantitative assessment of parasitemia levels, while a thin blood smear is necessary for the precise identification of the plasmodium species.
What goals does radical malaria therapy achieve?
Radical therapy aims to eradicate persistent tissue forms (hypnozoites in Pl. vivax and Pl. ovale) or sexual forms (gametocytes in Pl. falciparum) to prevent relapses and further transmission.
What else to study on this topic
- Morphological and cultural features of Yersinia pestis
- Characteristics of Francisella tularensis subspecies and biovars (tularensis, holarctica, mediaasiatica)
- Clinical and morphological classification of infections by organ localization
- Differential diagnosis of malarial coma and encephalopathies
- Mechanisms of microbial evasion from the host immune response
Master the complete topic in the «Infectious Diseases» course
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Other topics in the section "Zoonotic infections — 2024 study guide"
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