Overview of Chikungunya Fever
Chikungunya fever is an acute infectious disease caused by Chikungunya virus (CHIKV), transmitted by Aedes aegypti mosquitoes, and characterized by fever, rash, and joint pain.The first epidemic of Chikungunya fever was confirmed in Tanzania in 1952, and the virus was isolated in 1956. The disease is mainly endemic in Africa and Southeast Asia, and in recent years it has caused large-scale epidemics in the Indian Ocean region.
Causes
Chikungunya fever is caused by Chikungunya virus (CHIKV), Aedes aegypti and Aedes albopictus are the main vectors of the disease. Transmission occurs primarily through the bite of virus-infected Aedes aegypti mosquitoes. It may be transmitted by aerosol in the laboratory, but no direct human-to-human transmission has been reported.
Population susceptibility: Humans are generally susceptible to CHIKV, and infection can manifest as either overt or latent infection.
CHIKV can multiply and produce cytopathic lesions in cells such as Vero, C6/36, BHK-21 and HeLa. It is not susceptible to blood cells such as primary lymphocytes, T-lymphocytes, B-lymphocytes, and monocytes.CHIKV can infect non-human primates, mammary rats, and other animals.
Symptoms
The incubation period of the disease is 2 to 12 days, usually 3 to 7 days.
1. Acute phase
(1) Fever The patient often starts suddenly with chills, fever, body temperature up to 39℃, accompanied by headache, nausea, vomiting, loss of appetite and enlarged lymph nodes. Generally, the fever can subside in 1-7 days, and some patients have a mild fever again after about 3 days (bimodal fever), which lasts for 3-5 days and returns to normal. Some patients may have conjunctival congestion and mild photophobia conjunctivitis manifestations.
(2) Rash 80% of the patients in the onset of 2 ~ 5 days, the trunk, limbs of the extension side, palms and soles of the feet appeared rash, for the spot rash, papules or purpura, the skin between the rash is mostly normal, some patients accompanied by a sense of itching. The rash subsides after a few days and may be accompanied by slight flaking.
(3) Arthralgia At the same time of fever, several joints and spine have pain and joint swelling, which may be accompanied by generalized myalgia. The joint pain is mostly migratory, worsens with movement, and is worse in the morning. The disease progresses rapidly, often with loss of joint function and immobility within minutes or hours. It mainly involves small joints, such as the hand, wrist, ankle and toe joints, but may also involve large joints, such as the knee and shoulder. Severe pain caused by wrist compression is a characteristic feature of this disease. Joint effusion is rare. x-ray examination is normal.
(4) Others A very small number of patients may develop meningoencephalitis, hepatic impairment, myocarditis and skin and mucous membrane bleeding.
(2) Recovery period
After the acute stage, joint pain and stiffness can be completely recovered in the majority of patients. In some patients, persistent joint pain and stiffness can last for several weeks to months, or even more than 3 years. Individuals may have sequelae such as impaired joint function.
Examination
1. General examination
(1) Routine blood test The white blood cell count is mostly normal, but the total number of white blood cells and lymphocytes are reduced in a few patients, and platelets are mildly reduced.
(2) Biochemical examination: Serum ALT, AST and creatine kinase (CK) are elevated in some patients.
(3) Cerebrospinal fluid examination Cerebrospinal fluid examination in patients with meningoencephalitis is consistent with the changes of viral injury.
2. Serologic examination
(1) Serum specific IgM antibody: ELISA, immunochromatography, etc. The results of IgM antibody detection by capture method are more reliable. Generally, IgM antibodies appear on the first day after the onset of disease, and most patients are positive on the fifth day.
(2) Serum-specific IgG antibodies are detected by ELISA, immunofluorescent antibody assay (IFA), and immunochromatography. Generally, IgG antibodies appear on the second day after the onset of the disease, and most patients are positive on the fifth day.
3. Pathogenetic examination
(1) Nucleic acid test Nucleic acid amplification methods such as RT-PCR and Real-timePCR are used. Generally, viral nucleic acid can be detected in the serum of most patients within 4 days after the onset of disease.
(2) Virus isolation Collect serum specimens from patients within 2 days of the onset of disease and isolate the virus using sensitive cells such as Vero, C6/36, BHK-21 and HeLa.
Diagnosis
Diagnosis is based on:
1. epidemiologic information
Living in Chikungunya fever endemic area or history of travel to an infected area within 12 days, history of mosquito bite within 12 days prior to onset of illness.
2. Clinical manifestations
Acute onset, with fever as the first symptom, rash in 2-5 days of illness, severe pain in several joints.
3.Laboratory tests
(1) Positive serum specific IgM antibody;
(2) The serum specific IgG antibody titer in the recovery phase is more than four times higher than that in the acute phase;
(3) Detection of chikungunya virus RNA from patient specimens;
(4) Isolation of chikungunya virus from patient specimens.
Diagnostic criteria: suspected diagnosis: with the above epidemiologic history and clinical manifestations; without epidemiologic history, but with the above typical clinical manifestations. Definitive diagnosis: suspected diagnosis based on the presence of any one of the laboratory tests in the diagnostic basis.
Differential diagnosis
1. Dengue fever
Chikungunya fever and dengue fever have the same vector, the same endemic area and similar clinical manifestations, which makes it difficult to differentiate from dengue fever. Chikungunya fever has a shorter fever period, arthralgia is more pronounced and lasts longer, and bleeding tendency is lighter. Differentiation depends on specific laboratory tests.
2. O’nyong-nyong and other alphavirus infections
O’nyong-nyong virus, Mayaro virus and other alphaviral infections are similar to chikungunya fever in clinical manifestations, and are not easy to be differentiated based on clinical manifestations and general laboratory tests, but require specific tests for differential diagnosis. Because of the antigenic crossover between these viruses, serological results need to be carefully analyzed. Nucleic acid testing and virus isolation are the main methods of identifying these viral infections.
3. Infectious erythema
Caused by fine virus B19, erythema of the zygomatic region with perioral pallor first appears, followed by maculopapular rash on the trunk and limbs after 2 to 5 days. Joint damage manifested as polyarticular periarticular inflammation, more frequent in the proximal phalanges, metacarpophalangeal joints, and may invade the wrist, knee and ankle joints. Positive antibody and nucleic acid test for microvirus B19.
4. Other
This disease should be distinguished from influenza, measles, rubella, infectious mononucleosis, rheumatic fever, bacterial arthritis and other diseases.
Treatment
There is no specific drug treatment for this disease, mainly for symptomatic treatment.
1. General treatment
During the period of fever, bed rest should be provided, and it is not advisable to go down to the ground too early to prevent aggravation of the disease. Take anti-mosquito isolation measures.
2. Symptomatic treatment
(1) Cooling down the body temperature of patients with high fever. Patients with obvious bleeding symptoms should avoid alcohol bath. Non-steroidal anti-inflammatory drugs can be used, avoid the use of aspirin drugs.
(2) Analgesia Analgesic drugs can be used for more severe joint pain.
(3) Treatment of meningoencephalitis The main point of treatment is to prevent cerebral edema. Mannitol, tachycardia and other drugs can be used to lower the cranial pressure.
(4) Rehabilitation Rehabilitation can be given to people with joint pain or impaired mobility.
Prevention
Chikungunya fever can be prevented by the following measures.
1. Control the source of infection
Try to treat locally to minimize the chance of transmission. During the period of viremia, patients should be isolated by mosquito prevention. The isolation period is 5 days after the onset of illness. Suspected and confirmed cases should be reported in time.
2. Cut off the transmission pathway
There should be mosquito nets, screen windows, screen doors and other anti-mosquito equipment in the sick room. Eliminate mosquitoes and remove mosquito breeding sites.
3. Protect susceptible people
At present, there is no vaccine available. Mainly take personal anti-mosquito measures.