Taxonomy and virus properties
The dengue virus belongs to the family Flaviviridae and the genus Flavivirus. There are 4 serotypes of the virus. Although they are antigenically similar, there are significant differences between them. A previous infection induces immunity only to the serotype that caused it (for no more than 2 years), while cross-protection against other serotypes is partial and temporary. Therefore, a person can be reinfected.
The causative agent is thermolabile, meaning it is rapidly destroyed by heat. It exhibits pronounced hemagglutinating activity: it is capable of agglutinating human erythrocytes (group 0), as well as those of geese and chickens.
In laboratories, the virus is cultivated:
- In animals: newborn white mice are most commonly infected intracerebrally or intraperitoneally.
- In chicken embryos: by inoculation into the yolk sac.
- In cell cultures: a cytopathic effect is observed (especially in serotypes 2 and 3), and plaques are formed.
- In mosquito cells: reproduction occurs with the formation of symplasts.
Epidemiology
Dengue fever is a zoonotic (natural focal) arboviral infection prevalent in tropical and subtropical regions (from 42° N to 40° S). The transmission route is vector-borne; a single bite from an infected mosquito is sufficient.
Two epidemiological types are distinguished:
- Urban: the source and reservoir is humans, the vector is the mosquito Aedes aegypti.
- Jungle (sylvatic): the reservoir includes monkeys (in which the disease is asymptomatic), lemurs, bats, and squirrels. The vector is Aedes niveus, which bites both animals and humans, transmitting the virus to cities.
In nature, the virus persists through transovarial transmission: infected mosquitoes transmit the pathogen to their offspring.
Pathogenesis and clinical forms
The virus multiplies in the salivary glands of the mosquito and enters the bloodstream upon a bite. The incubation period lasts from 3 to 15 days. The pathogenesis includes the following phases: primary replication (in lymph nodes and endothelium), primary viremia (at the end of incubation), dissemination (involvement of target organs), and secondary viremia.
The disease can occur in two forms:
- Classical: manifests with the clinical triad (fever, intoxication, hemorrhagic syndrome). Characterized by a characteristic gait (due to severe muscle and joint pain, hence the name dandy), a biphasic temperature curve, lymphadenopathy, and a maculopapular rash on days 5–6. It often runs asymptomatically.
- Hemorrhagic: develops acutely, accompanied by high fever, hepatomegaly, prominent petechiae, and hemorrhages. Mortality reaches 40–50%, often complicated by shock syndrome.
The pathogenesis of the hemorrhagic form is explained by the immunopathological hypothesis (antibody-dependent enhancement of infection). It occurs upon reinfection with a different serotype, especially in children. Virus-antibody complexes are formed, and complement is activated. The virus penetrates phagocytes and actively multiplies there, leading to a massive release of biologically active substances and severe capillarotoxicity.
Microbiological diagnostics
Research materials include the patient's blood, autopsy material, or vector mosquitoes themselves.
Two main methods are used:
- Virological (virus isolation): bioassays on mosquitoes (inoculation into the thorax or head) or suckling mice, inoculation of cell cultures. The virus is identified using DFA (direct immunofluorescence assay) with monoclonal antibodies.
- Serological (detection of antibodies): paired sera are examined. The following reactions are used: neutralization test (NT), hemagglutination inhibition test (HIT), complement fixation test (CFT), and ELISA.
Briefly: answers to topical questions
What structural and non-structural proteins are part of the dengue virion?
The dengue virion contains only structural proteins, whereas non-structural proteins facilitate the reproduction process.
- Capsid protein (C) — forms the internal protein shell.
- Membrane protein (M) — a structural component of the virion.
- Surface protein (E) — a dimer that determines cell tropism and serves as the main immunogen.
Non-structural proteins (NS1–NS5 and viral RNA polymerase) are encoded in the genome but are not incorporated into the virion itself.
Which immunoglobulin classes are detected by ELISA to diagnose the acute phase of dengue fever?
To diagnose recent flavivirus infection by ELISA, class M immunoglobulins (IgM) are detected.
Serological diagnostics involves examining paired blood sera; the diagnostic criterion is a 4-fold or greater rise in antibody titer.
What medications are used for specific etiotropic treatment of dengue fever?
Specific etiotropic treatment for dengue fever has not been developed.
The source also indicates emergency prophylaxis: administration of specific immunoglobulin or immunoglobulin from the plasma of donors residing in endemic zones.
Class and exam questions
Why is dengue fever referred to as the "dandy" fever?
The name comes from a distorted version of the English word dandy. Due to severe muscle and joint pain, patients change their posture and develop a characteristic stiff or swaggering gait.
Can you get dengue fever more than once?
Yes, it is possible. There are 4 virus serotypes. A previous infection provides immunity to only one serotype, and cross-protection against others is only partial.
What is the essence of the antibody-dependent enhancement of infection phenomenon?
Upon reinfection with a different virus serotype, defective immune complexes are formed. They help the virus enter macrophages, where it actively multiplies, causing severe hemorrhagic syndrome.
What else to study on this topic
- Detailed mechanism of antibody-dependent enhancement of infection
- Comparison of urban and jungle epidemiological types
- Methods of virus cultivation in laboratory conditions
- Differential diagnosis of classical and hemorrhagic forms
- Principles of emergency prophylaxis application
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