Sadfly fever is an acute natural focal infection caused by a filtered arbovirus and occurring with a short–term febrile syndrome. Disease is accompanied by febrile fever, headaches and muscle pains, eye reactions (symptoms of Peak and Taussig), hyperemia of the face and neck, hemorrhages, meningeal phenomena, prolonged asthenic syndrome. Recognition is carried out on the basis of epidemiological history, clinical picture, serological and virological studies. Treatment is symptomatic; it includes detoxification therapy, taking antipyretics, cardiovascular drugs, vitamins.
General information
Sadfly fever (mosquito-borne, three-day, phlebotomy fever, pappataci fever) is a transmissible viral disease with a characteristic short-term fever, pronounced myalgia, pathognomonic reactions from the eyes, neurological symptoms. The distribution area of sadfly fever coincides with the habitat of mosquito vectors and covers tropical and subtropical regions (the Mediterranean, the Balkans, the Middle East, East and West Africa, South and Southeast Asia and Central Asia). The incidence of sadfly fever is characterized by a strict spring-summer seasonality with two peaks (May-June, July-August) due to the breeding of mosquitoes. Sadfly fever develops more often in non-immune people who come to endemic areas for the first time; indigenous people have immunity due to a disease suffered in early childhood.
Causes
Sadfly fever is caused by 5 serotypes of a filtered RNA genomic virus from the bunyanovirus family. Viral particles are sensitive to heat, exposure to disinfectants, but are resistant to low temperatures; they remain in the dried state for up to 3-7 months. There are natural and anthropurgical foci.
The source of the virus is infected wild and synanthropic rodents or a sick person in the stage of virology. Specific carriers of the pappataci fever virus are flying blood–sucking insects – female mosquitoes Phlebotomus papatasii. When feeding on the blood of sick animals and humans in the initial period of the disease, the pappataci fever virus enters the mosquito’s body, multiplies and remains in it for life, being transmitted to the next generations transovarially. Sadfly fever is transmitted to humans most often by vector-borne bites of infected mosquitoes; the possibility of parenteral infection through insufficiently treated medical instruments is not excluded.
Mosquito bites are accompanied by redness of the skin, swelling, formation of an itchy nodule, scratching. In the human body, the sadfly fever virus affects the cells of the monocyte-macrophage system, where it is rapidly reproduced during the incubation period and enters the bloodstream in the first 2-3 days of the disease with the development of generalized viremia. Due to a certain neurotropicity, the pappataci fever virus settles in the cells of the central nervous system, causing a violation of its functions, leading to cerebral hypertension. The changes also affect small vessels and muscles.
Symptoms
The duration of the incubation period of sadfly fever is from 3 to 9 days. The disease has an acute, sudden onset with severe chills and a sharp jump in temperature to 38-41C. Sadfly fever is accompanied by severe headache in the temporal and frontal zones; sharp myalgia, especially in the calf muscles, back and lower back; pain along the nerve trunks. Pathognomonic eye reactions are noted: limited injection of sclera at the outer corners of the eyes in the form of a triangle with a vertex directed to the cornea (Peak symptom), severe pain when moving the eyes, pressing on the eyeball and trying to lift the upper eyelid with fingers (Taussig symptom), photophobia, conjunctivitis.
There is a noticeable puffiness of the face and neck, hyperemia of the mucous membrane of the pharynx with spot hemorrhages, swelling of the palatine arches and tongue. Herpes rashes may appear on the lips, macular or urticaria rash and small–point hemorrhages on the skin. Nasal and gastrointestinal bleeding may occur. In severe forms of sadfly fever, neurological symptoms appear: dizziness, hyperesthesia, meningeal phenomena, anxiety, excitement, delirium, loss of consciousness. Often there is bloating, nausea, vomiting, frequent up to 5-6 times a day, loose stools with an admixture of mucus.
The duration of the febrile period is determined by the severity of the clinical course of sadfly fever: in mild form, the fever phase lasts 1-2 days, in moderate – 3-4 days, in severe – up to 8 days. The temperature drops critically to normal or subfebrile indicators, which is accompanied by sharp weakness and heavy sweat, bradycardia. The period of convalescence is long; it lasts for several weeks and proceeds with severe asthenia, neuralgia, depression and decreased performance. Sometimes there are trophic disorders, manifested by hair loss, brittle nails. Complications are rarely noted in the form of pneumonia, infectious psychosis.
Diagnostics
The basis for the diagnosis of sadfly fever is the data of the epidemiological history (endemic area, seasonality, mass of the disease), the characteristic clinical picture (acute onset, short duration of fever, pronounced myalgia, symptoms of Peak and Taussig), laboratory tests (general blood analysis, serological reactions, virological method).
In the blood of a patient with sadfly fever, there is an increasing leukopenia with a shift to the left, lymphopenia, aneosinophilia, monocytosis. Lumbar puncture and analysis of cerebrospinal fluid reveal signs of increased cerebrospinal fluid pressure, moderate cytosis and high protein content. The diagnosis confirms the isolation of the virus from the blood and cerebrospinal fluid during the febrile period by intracerebral infection of newborn mice. Serological studies (NR, IFT, HI with paired sera) conducted on the 2-3 day of the disease and 2-3 weeks after that show an increase in the titer of specific antibodies. Differential diagnosis is carried out with influenza, malaria, typhus and tick-borne recurrent typhus, dengue fever, a non-jaundiced form of leptospirosis, enterovirus fever, etc.
Treatment and prevention
Patients are subject to hospitalization in an infectious hospital. There is no specific treatment for mosquito fever; in the acute period, patients are shown bed rest, sufficient drinking load, and vitamin intake. Medical support includes detoxification and symptomatic therapy (the appointment of antipyretics and cardiovascular agents; with intracranial hypertension – diuretics). Discharge of patients who have had sadfly fever is carried out 2-3 weeks after the onset of the disease (on the 7th-10th day of apirexia).
The outcome is favorable: complications are quite rare, in some cases relapses are possible. Prevention of the spread of sadfly fever involves the destruction of adult mosquitoes and their breeding centers (rodent burrows, cracks and cracks in the walls and floors of buildings, garbage dumps), insecticidal treatment of household buildings and dwellings, protection of people from mosquito bites (equipment of vestibules, the use of nets on windows and curtains over the bed, wearing protective overalls and nets, impregnated with repellents). Specific prevention of sadfly fever is carried out with an embryonic formalized vaccine 2 months before the start of the epidemic season.
