lā shā bì ng dú
2 English referenceLassa virus
LASV
3 Chinese nameLassa virus
4 English nameLassa virus; LASV
5 Taxonomic type
Species
6 ClassificationSchistosoma family > genus Sandy >. Virus
7 Basic Lassa virus characteristicsLassa viral hemorrhagic fever is an acute disease occurring in West Africa with a 14-week duration. Although first described in the 1950s, it was not identified as the virus causing the disease until 1969. Lassa virus is a single-stranded RNA virus belonging to the genus Sarcovirus in the family Sarcoviridae. Lassa fever is known to be endemic in parts of Guinea (Conakry), Liberia, Sierra Leone, and Nigeria, and may also be present in other West African countries.
The causative agent of Lassa viral hemorrhagic fever is Lassa fever virus, a member of the genus Serratovirus in the family Serratoviridae. Viral particles range from round to polymorphic, with a capsule membrane, the surface of the viral envelope has a "T" type protrusion, length 7-10nm, composed of viral glycoproteins. The viral genomic RNA is present in the viral particles in the form of a circular nucleocapsid, with a length of 400 nm to 1300 nm. The inside of the viral particle usually contains electron dense particles, which are sandy red in color under electron microscopy, for which the sand grain virus is named, and its electron dense particles are the ribosomal components of the host.
The viral nucleic acid is a two-segmented negative-stranded RNA, with a large segment called L RNA, 7200 kb in length, with a molecular weight of about 2.2-2.8 × 106 d, and a small segment called S RNA, 3400 bp in length, with a molecular weight of about 1.1 × 106 d. The 3' ends of the L and S RNA segments have 17/19 nucleotides that are identical. 19 nucleotides are identical and are reverse complementary to the sequence at the 5' end of the genome. This conserved sequence at the end of the viral genomic RNA may be the viral RNA-dependent RNA polymerase recognition and binding site. The starting point for replication of viral RNA may lie in an intramolecular duplex generated by the two ends of L or S RNA alone, or in an intermolecular duplex formed by annealing the L and S RNA ends to each other.
8 Signs and Symptoms of Lassa Virus InfectionAbout 80% of human infections are asymptomatic; the remaining cases are severe multisystemic illnesses in which the virus attacks several organs of the body, such as the liver, spleen, and kidneys. The incubation period for Lassa fever is 621 days. The disease is usually progressive, beginning with fever, generalized weakness and malaise. After a few days headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain may develop. Severe cases may progress to swelling of the face, fluid in the chest, bleeding from the mouth, nose, *** or gastrointestinal tract, and low blood pressure. Proteinuria may also occur. Shock, seizures, tremors, disorientation, and coma may be seen in advanced stages.
Deafness occurs in 25% of patients, with half of them regaining some function after 13 months. Transient hair loss and unsteady gait may occur during recovery. Morbidity and mortality Some studies suggest that 300,000 to 500,000 cases of Lassa fever and 5,000 deaths occur annually throughout West Africa. The overall morbidity and mortality rate is 1%, but can be as high as 15% among hospitalized patients. Death usually occurs within 14 days of the onset of fatal cases. The disease is particularly severe in the second trimester of pregnancy, with maternal and/or fetal death occurring in more than 80% of cases during the last trimester.
9 Animal hosts of Lassa virusLassa fever is a zoonotic disease in which a person becomes infected through contact with an infected animal. The animal host of Lassa virus is a rodent of the genus Mastomys, commonly known as the "whelping mouse". Mastomys rats infected with Lassa virus do not develop disease, but they can release the virus into their feces (urine and stool).
10 People at risk for Lassa feverLassa fever occurs among men and women of all age groups. Persons at risk are those living in rural areas where Mastomys rats are usually found, especially in areas with poor sanitation or crowded living conditions. Failure to maintain appropriate isolation care and infection control norms can jeopardize health care workers.
11 Transmission of Lassa virusHumans are commonly infected with Lassa virus through exposure to the feces of infected Mastomys rats. Direct exposure (contact with feces) and Lassa virus can also be transmitted from person to person through direct contact with blood, urine, feces, or other bodily secretions of a person with Lassa fever. There is no epidemiologic evidence to support airborne transmission between people. Interpersonal transmission can occur in both community and health care settings, where the virus can be transmitted through contaminated medical equipment such as reused needles. Sexual transmission of Lassa virus has been reported.
12 Laboratory TestsEarly blood leukocytes are decreased and later increased, thrombocytopenia, and prolonged prothrombin time.? Urine has protein, cells and tubular pattern. Blood creatinine phosphokinase, lactate dehydrogenase and aminotransferases may rise in severe cases.
13 Diagnosis of Lassa feverBecause the symptoms of Lassa fever are so varied and nonspecific, it is often difficult to make a clinical diagnosis, especially early in the course of the disease. Lassa fever is difficult to distinguish from many other diseases that cause fever, including malaria, shigellosis, typhoid fever, yellow fever, and other viral hemorrhagic fevers.
Definitive diagnosis requires testing that only highly specialized laboratories can perform. Laboratory specimens can be harmful and must be handled with extreme caution. Lassa fever is diagnosed by finding Lassa antigen, anti-Lassa antibodies, or virus isolation techniques.
14 Treatment of Lassa feverThe patient should be placed on bed rest with attention to water and electrolyte balance and symptomatic treatment. Early application of immune plasma or recovery serum treatment, the effect is not satisfactory. In recent years, the application of the antiviral drug ribavirin (ribavirin) to treat early patients (within 6 days of the onset of the disease) has achieved better results, with the disappearance of viremia and a significant decrease in the morbidity and mortality rate. There is no evidence to support the role of ribavirin as prophylaxis after Lassa fever exposure.
15 Prevention of Lassa feverLassa fever is extremely contagious and should be closely isolated. Contact with the patient should wear a mask and gloves, wear isolation clothing. Excreta and contaminants should be strictly disinfected. Isolation time 34 weeks. Urinary excretion of virus for a long time, should be continuous urine virus examination. Laboratory examination specimens are infectious and should be handled safely. For blood leukocyte count, acetic acid (20 mg/L, PH 2.9) should be added. Check the leukocyte sorting smear fixed with glutaraldehyde and heated to 60 ℃, which can inactivate the virus. Check the blood electrolytes and other heat-resistant substances, heat first before checking.
Prevention of Lassa fever in the community focuses on promoting good "community hygiene" to keep rodents out of homes. Effective measures include storing grain and other food in rodent-proof containers, disposing of garbage away from the home, keeping the home clean, and owning a cat. Because Mastomys rats are extremely abundant in endemic areas, it is impossible to completely eliminate them from the environment.
Family members and health care workers should always take great care to avoid contact with blood and body fluids while caring for the patient. Routine isolation care precautions may be able to prevent the spread of Lassa virus in most cases. However, to be more complete, patients suspected of having Lassa fever should be cared for under specific "isolation precautions", which include the wearing of protective clothing, such as masks, gloves, gowns and face shields, and the systematic disinfection of contaminated equipment (see also details in "Infection control of viral haemorrhagic fevers in African health-care settings"). Infection Control of Viral Hemorrhagic Fever in African Health Care Settings" for detailed guidelines).
In rare cases, travelers from areas where Lassa fever is endemic have brought the disease to other countries. Although malaria, typhoid fever, and many other tropical infections are more common, a diagnosis of Lassa fever should be considered in patients with fever returning from West Africa, especially if they have been exposed in rural villages or hospitals in countries where Lassa fever is known to be endemic. Health care workers who see patients suspected of having Lassa fever should immediately contact local and national experts for advice and to arrange for laboratory testing.
16 Prognosis