Mosquito-Borne Viral Diseases
Mosquito-borne viral diseases, caused by arboviruses (arthropod-borne viruses), are acute infections that often produce striking skin signs. The three most common arboviruses in the tropics are dengue virus (DENV 1–4), Zika virus (ZIKV) and chikungunya virus (CHIKV), all spread mainly by Aedes mosquitoes (Aedes aegypti and Aedes albopictus).
When an infected mosquito bites, the virus enters local antigen-presenting cells (epidermal Langerhans cells and dermal macrophages), multiplies and then spreads into the bloodstream. Although all three are carried by mosquitoes, each virus favors different cells and so produces its own skin picture: a flushed “islands of white in a sea of red” rash with pinpoint bleeding in dengue, a prominent itchy papular rash with conjunctivitis in Zika, and persistent post-inflammatory hyperpigmentation (the “Chik sign”) with severe joint pain in chikungunya.
At Haute-Derma, rashes caused by mosquito-borne viruses are managed with a standardized pathway of risk stratification and layered treatment: vascular dermoscopy, rapid NS1 antigen and IgM/IgG tests, close monitoring of platelet counts and hematocrit, skin barrier repair, and Nd:YAG laser for long-lasting hyperpigmentation.
How the Viruses Affect Blood Vessels and the Skin’s Immune Response
Viral Replication and Dermal Inflammation
- The Aedes mosquito injects the virus into the dermis. The virus binds to DC-SIGN receptors on Langerhans cells, travels to the regional lymph nodes and replicates heavily, leading to viremia.
- Virus in the blood activates T cells and macrophages, which release a wave of inflammatory cytokines (TNF-alpha, IL-6, IFN-gamma). These dilate superficial vessels and make them leaky, producing a red maculopapular exanthem.
Antibody-Dependent Enhancement (ADE) and Plasma Leakage in Dengue
- On a second infection with a different dengue serotype, existing antibodies bind the new virus without neutralizing it. These immune complexes enter macrophages more easily through Fc-gamma receptors (antibody-dependent enhancement, ADE).
- The dengue NS1 protein damages the glycocalyx lining blood vessel cells, causing plasma leakage, reduced circulating volume and pinpoint bleeding under the skin (petechiae).
Chronic Dermal Hyperpigmentation in Chikungunya
- Chikungunya virus has a strong affinity for dermal fibroblasts. The inflammation it triggers overstimulates melanocytes, which produce more melanin that drops into the deep dermis, creating the typical pigmentation on the face and over the joints.
Clinical Features of the Characteristic Rashes
Dengue Fever Rash:
- Early phase (days 1–3): Diffuse flushing over the whole body, with a slightly raised redness of the face and chest resembling sunburn or a roseola-type rash.
- Recovery phase (days 5–7): The characteristic Herman rash, with patches of normal white skin scattered through confluent redness, known as “islands of white in a sea of red.” Patients also have small petechiae on the forearms and lower legs and intense itching of the palms and soles.
Zika Virus Rash:
- Appearance: A bright pink maculopapular rash that starts on the face and quickly spreads outward to the trunk and limbs within 24–48 hours.
- Associated features: Moderate to marked itching. Key clue: Non-purulent conjunctivitis in both eyes, with low-grade fever and mild joint aches.
Chikungunya Rash:
- Appearance: A red maculopapular rash appears on days 2–5 of fever, concentrated on the trunk and the flexural surfaces of the limbs.
- Distinctive lesion (Chik sign): Dark brown to black, butterfly-shaped pigmentation across the bridge of the nose and cheeks, or dark patches over the knees and wrists. Severe pain in many small joints forces patients to stoop as they walk (“chikungunya” means “that which bends up”).
Differential Diagnosis of Acute Arboviral Rashes
| Dengue fever | Zika virus disease | Chikungunya |
|---|---|---|
| “Islands of white in a sea of red” plus petechiae | Pink maculopapular rash that spreads quickly | Maculopapular rash plus Chik sign hyperpigmentation |
| Marked itching in the recovery phase | Marked itching from the start | Mild to moderate itching |
| Mucosal bleeding, low platelets | Non-purulent conjunctivitis | Severe, persistent joint pain |
| Dark red petechiae that do not blanch | Uniform dilation of the superficial vascular network | Melanin deposits in the dermis |
| Shock from plasma leakage, organ failure | Microcephaly in the unborn baby | Long-lasting chronic arthritis |
How We Diagnose These Infections at Haute-Derma
Dermoscopy and Diascopy (Glass Pressure Test): Vascular dermoscopy clearly separates a congestive rash (which blanches under glass pressure) from bleeding into the skin (which does not blanch, a negative diascopy).
Urgent Blood Count and Chemistry: Close tracking of how fast platelets are falling (thrombocytopenia) and whether hematocrit is rising (a sign of hemoconcentration from plasma leakage in dengue).
Molecular and Serologic Testing:
- Rapid NS1 antigen test (dengue): Done within the first 1–5 days of fever.
- Real-time RT-PCR (dengue/Zika/chikungunya): Precisely identifies viral RNA in blood or urine.
- IgM/IgG antibody tests: Done from day 5 onward to confirm an acute immune response.
Treatment and Recovery Care at Haute-Derma
General Medical Support
- Safe fever and pain relief: Plain paracetamol (10–15 mg/kg per dose). Aspirin, ibuprofen and other NSAIDs are strictly contraindicated because they raise the risk of stomach bleeding and severe platelet loss.
- Oral rehydration: Drink oral rehydration solution (ORS) and fruit juice regularly to limit hemoconcentration.
Skin Barrier Repair and Itch Relief
- Moisturizers containing ceramides, niacinamide, zinc oxide and calamine soothe the intense itching and burning during the recovery phase of the rash.
- Bathe in lukewarm water with a soap-free cleanser and avoid scratching, which can break the skin and lead to bacterial superinfection (Staphylococcus aureus).
Treating Residual Hyperpigmentation (Chik Sign) at Haute-Derma
- Short-pulsed 1064 nm Nd:YAG laser (PTP/toning mode): Breaks up melanin deposited in the deep dermis after chikungunya, evening out skin tone without damaging the epidermal surface.
- Low-level light therapy (LLLT, 630 nm red light): Stimulates cell renewal, calms persistent dermal inflammation and speeds skin recovery.
