Ross River virus is an acute viral disease with a transmissible pathway of infection. The main symptoms are polyarthritis, tendovaginitis and rash. The disease is also manifested by fever, moderate intoxication syndrome, a violation of the psycho–emotional state, less often – lymphadenopathy, paresthesia of the extremities. The diagnosis of pathology is reduced to the detection of the pathogen antigen in the blood and synovial fluid, the detection of antibodies. There is no etiotropic therapy, treatment is symptomatic, aimed at relieving joint pain syndrome, lowering body temperature and detoxification.
B33.1 Ross River virus disease
Ross River virus (Ross River fever, epidemic polyarthritis) is included in the category of infectious diseases with predominant damage to joints and ligaments. The first descriptions of fever date back to 1928, when annual outbreaks of an unknown disease were noted in the Ross River Valley (Australia). In 1963, a scientist at the University of Cleveland Doherty isolated the virus. In some areas there is no seasonality, but more often the pathology is detected from January to May, it is common in such states as Australia, Oceania, Fiji, Samoa, Cook Islands. Mostly men are ill. Risk groups are rural residents, children, veterinarians, tourists.
The causative agent of the infection is an RNA–containing arbovirus of the same name, belonging to the Togavirus family. Sources and reservoirs of infection in the wild are considered to be gray kangaroo, wallaby, New Holland mouse, in which the disease is mostly asymptomatic. The carriers of infection are mosquitoes of the genus Aedes, among insects the virus can be transmitted transovarially. A feature of the life cycle of vectors is the high resistance of eggs to drying and preservation even far from a water source, this allows mosquitoes to maintain the population size, but makes it difficult to fight them. The way of transmission of infection to humans is mainly transmissible, infection is possible with blood transfusion, organ donation, use of non-sterile instruments, care and treatment of sick animals, repeated use of disposable syringes among injecting drug users, transplacentally (data about the latter are extremely contradictory).
After the bite of an infected mosquito, the pathogen attaches to the white blood cell integrin protein and migrates with the blood flow into the striated musculature. The primary replication of the virus occurs in skeletal myocytes, then the arbovirus enters the bloodstream, where it can be neutralized by antibodies and interferon-1, affects macrophages, penetrating with them into other organs and tissues, showing tropicity to articular cartilage. Joint pathology is caused by the loss of proteoglycans and thinning of cartilage due to inflammatory changes involving macrophages infected with the virus. The inability of the body to generate cytotoxic T-lymphocytes, whose function includes the ability to destroy macrophages with a virus, can cause the development of chronic arthritis and arthralgia. In 2015, data from studies of the body’s immune response to the presence of the virus were published, according to which a deficiency of arginase-1 in muscle cells can exacerbate the pathogenic effect of the pathogen, which affects the duration and severity of Ross River virus.
The incubation period is from 3 to 21 days (usually 7-9 days). The disease begins acutely with an increase in temperature to 38 ° C, muscle pain, fatigue, various kinds of joint lesions in the form of polyarthritis, starting with a slight restriction of movement and progressing to a significant increase in the volume of the joints, their redness and swelling. Movements in the involved limbs are significantly limited. The lesion is always symmetrical, the metacarpophalangeal, ankle, metacarpal and knee joints are more often affected. With pronounced edema, nerve compression occurs and the appearance of a false sensation of numbness, “goosebumps” (paresthesia). To alleviate the condition, patients can take a forced position, avoid movements.
Half of the patients with this nosology have a rash on the skin of the trunk, limbs, fingers, face, palms, soles, scalp. The elements of the rash are spots, bumps (papules), less often bubbles, do not itch, do not peel. There may be a painless enlargement of the lymph nodes and spleen, detected only when examined by a doctor. There may be blood in the urine (hematuria), diarrhea. In half of the cases, patients complain of malaise and fatigue, which is usually manifested by a slowdown in reactions, a decrease in productivity. Only 3 cases of meningitis and encephalitis involving the Ross River virus have been described, however, with the appearance of severe headache, gushing vomiting at the peak of cephalgia, convulsions, disorders of consciousness, damage to the brain and its membranes cannot be excluded.
The course of the disease is often benign, mild or moderate. The appearance of complications indicates the untimeness of contacting a doctor, the duration and aggravation of the pathological process (including self-medication). The most common complications are arthropathies, secondary purulent processes (bursitis, arthritis, myositis, streptodermia), chronic course of arthritis. Prolonged compression of nerve fibers by swollen periarticular tissues contributes to the preservation of paresthesia after recovery, casuistically – nerve atrophy. In the presence of brain damage, edema of the brain substance may develop.
Consultations of an infectious disease specialist, rheumatologist, dermatovenerologist are necessary to resolve the issue of verification of the alleged diagnosis. With symptoms of central nervous system damage, a neurologist’s examination is required. A thorough collection of epidemiological anamnesis, an integrated approach to laboratory and instrumental diagnostics is important. Mandatory diagnostic procedures are:
- Objective inspection. Physical examination reveals instability of the emotional and mental status of the patient, maculopapular rashes, swelling and soreness in the joints, hyperemia and hyperthermia of the skin in the periarticular zone, splenomegaly, enlarged lymph nodes. According to the indications, a spinal, articular puncture is performed with a visual assessment of transparency, the presence of suspension, and the color of the resulting liquid.
- Laboratory tests. A general blood test reveals leukocytosis, acceleration of ESR, less often thrombocytopenia, anemia, the appearance of mononuclears. In the biochemical analysis, there is an increase in the activity of CRP, sialic acids, creatinine, less often LDH, ALT, AST. General clinical examination of urine indicates the appearance of erythrocytes, leukocytes, infrequently – proteinuria. When analyzing intraarticular fluid, a large number of monocytes are detected.
- Identification of infectious agents. Since the pathogen is located mainly intracellularly, serological methods come to the fore in diagnosis. ELISA is carried out in the first week of illness and after 10-14 days. The diagnosis is confirmed with an increase in the titer of antibodies by 4 or more times. The PCR method makes it possible to identify the pathogen in synovial fluid, blood serum and cerebrospinal fluid, while the probability of detecting the virus in the bloodstream decreases in proportion to the duration of the disease.
- Radiation methods. Lung radiography is performed for the purpose of differential diagnosis and detection of complications. Ultrasound of the affected joints confirms the presence of articular effusion, intra-articular formations, allows you to evaluate the ligamentous apparatus. An abdominal ultrasound visualizes an enlarged spleen. Inflammatory changes during ultrasound of lymph nodes are usually absent.
Differential diagnosis is carried out with hemorrhagic fevers (Chikungunya, Ebola, Marburg, Lassa, dengue, GLPS, Rift Valley), measles, rubella, chickenpox, ixodic tick-borne borreliosis, mansonellosis, brucellosis, tuberculosis, gonococcal arthritis, syphilis, psoriasis, rheumatism, systemic lupus erythematosus, juvenile rheumatoid arthritis, sepsis, gout, deforming osteoarthritis, bursitis, myositis, tendovaginitis, allergic dermatitis, glomerulonephritis, pyelonephritis.
All patients with suspicion of this pathology require hospitalization. Bed rest until maintaining a stable normal body temperature for 3-4 days. The diet is non-specific, frequent fractional nutrition is recommended, the exclusion of heavy food for digestion, alcohol. The drinking regime can be adjusted depending on the degree of joint edema, pain, and the severity of paresthesia. Immobilization of the affected joints is carried out by tight bandages, orthoses, motor rest of the affected limbs is mandatory.
There is no specific treatment. Therapy is primarily aimed at reducing joint pain, provides for the use of anti-inflammatory analgesics (ibuprofen, paracetamol). Detoxification, antipyretic and other symptomatic agents are prescribed. There is a growing interest of researchers in the use of glycans, in particular, pentosan polysulfate for the relief of joint syndrome. Glucocorticosteroids are recommended to be administered with caution.
Prognosis and prevention
The prognosis depends on the duration of the period between the appearance of the first symptoms and seeking medical help. Recovery is observed on average after 1 month, in 10% of cases the symptoms persist for up to 3 months or more. Arthralgias can be observed for 1-3 years, the development of a chronic inflammatory process in the joints is possible. The mortality rate is 0.79%. There are no means of specific prevention (vaccines), but research is underway in Australia to develop drugs for vaccination of the population. Non-specific measures consist in timely detection, treatment of patients, the use of protective repellents, clothing, mosquito nets, drainage of basements, swamps, insecticidal treatment. When working with sick animals, it is necessary to use gloves and protective shields.