Lassa hemorrhagic fever ( Lassa GL ) - Causes, Symptoms and Treatment .MF .

August 12, 2017 17:52 | Infectious Diseases

For a group of particularly dangerous infections, in addition to Ebola and Marburg hemorrhagic fever, and include Lassa.Infection is also a natural focal endemic areas in tropical African countries.

Lassa hemorrhagic fever (Lassa GL) - an acute viral natural focal infectious disease characterized by severe intoxication, necrotizing ulcerative pharyngitis, lesions of many organs and systems, the development of hemorrhagic syndrome and severe complications, sometimes incompatible with the life of the patient.

historical and geographical distribution of the GL Lassa

infection gets its name from the town of Lassa (Nigeria), where it was first identified in 1969.West African countries are endemic for Lassa GL, there are recorded each year up to 500 000 cases of the disease.This is Nigeria, Guinea, Mali, Sierra Leone, Senegal, Mozambique, at least Central Africa (Central African Republic, Burkina Faso and others).Mortality in GL Lassa to 60% (average 40%) occurs at the end of the 2nd week of illness.In th

e case of infection of pregnant women fetal death occurs in 85% of cases.

One of the recent outbreaks of Lassa GL occurred in 2012 in Nigeria.Of the 623 cases 70 people died (mortality 11%).Over time, flash ill many medical workers caring for patients and their treatment.

Causes of Lassa Fever

Pathogen infections - Lassa virus, belonging to the family of arenaviruses (Arenaviridae).Electron microscopy can be seen up to a dozen of the ribosomes that resemble the sand (Latin for sand - arenaceus).The virion contains a single-stranded RNA, a lipid membrane, has a diameter of 150 nm, a spherical shape with fibers arranged on the surface.Lassa virus belongs to I class of danger of infectious agents (ie, is both individual and social danger).There are four subtypes of Lassa virus circulating in different regions of Africa.

GL Lassa,

virus Lassa virus is stable in the environment, but is sensitive to disinfectants (chloroform, ether).The secretions of sick animals and humans the virus can persist for a long time.

source of infection in endemic foci - it multimammate African rat (Mastomys natalensis), who not only lives in the steppe zone, but also is able to penetrate into human dwellings.The natural foci of infected to 17-19% of the rats.In the body of animal infection is often asymptomatic, but the virus persists for a long time and is excreted in the urine and saliva of rodents.

Lassa infection Source GL - multimammate African rat

sick person is a danger to others.The virus is contained in nasopharyngeal contents, blood, urine, saliva of the patient, as well as for a long time may be stored in a dried state, and the transfer of dangerous factors that may enter the patient selection (food, water, utensils, dust particles in the household items).The most dangerous blood of patients, and with it, and vomit with blood, sputum with blood.

infection mechanisms.

1) Contact-home mechanism when blood enters and patient secretions on broken skin and mucous membranes.
2) parenteral mechanism of using multiple instruments, insufficient processing tools for medical purposes, accidental puncture needle from the patient's medical staff.
3) Alimentary mechanism (food and waterways) in contact with the patient's secretions for food and water.Dangerous insufficiently cooked infected meat of animals from infected water sources.
4) the airborne mechanism (airborne and airborne dust) in the inhalation of infected patient secretions - mucus or dust particles.
5) sexual transmission.

susceptibility to GL Lassa high, ill, both adults and children, regardless of gender.Known and nosocomial outbreak of Lassa fever.Seasonality is absent, the incidence of recorded evenly throughout the year.

Immunity after undergoing persistent infection lasting (up to 10 years or more), repeat event has not registered the disease.Among the local population to 15% carry the infection without symptoms.

Pathogenic action of Lassa virus in the human body

1) The input gates of infection (according to the ways of infection) may be the mucous membranes of the eyes, respiratory tract, digestive tract, reproductive system, mikrotravmirovannye skin.Changes in the entrance gate of infection there, but there is a clear relationship of the pre-emptive destruction of an organ system and depending on the place of introduction of the virus.For example, the introduction of the digestive system through the mucous more signs of lesions of the gastrointestinal tract, as through the introduction of the airway - pneumonia, pulmonary edema and the like.

2) Next, the virus enters the blood (viraemia, toksinemiya) and spreads throughout the body (hematogenous dissemination) with the defeat of many organs and systems.

3) The main point of the application or the target - a vascular endothelium (the inner walls of blood vessels).The result of exposure to the virus Lassa - increased fragility of vessels of different caliber, which is accompanied by changes in hemostasis, the launch of DIC (disseminated intravascular coagulation), a manifestation of what the patient would hemorrhagic rash on the body, bleeding and bleeding (in the process may involve the intestines, myocardium,lungs, brain, kidneys, liver and other organs).

4) Maximum GL Lassa severity leads to complications (infectious and toxic shock syndrome, acute liver failure, acute adrenal insufficiency, etc.).At this stage, there can come death.

GL Clinical symptoms of Lassa

incubation period (from the time of infection until the first symptoms of the disease) by an average of 7-10 days, but can be shortened to 3 days or be extended to 21 days.

1) Onset. difference from other vysokozaraznyh fevers (Ebola, Marburg) - beginning with GL
disease Lassa relatively gradual.Patients with symptoms of infectious-toxic syndrome (fatigue, feeling of weakness, fatigue, myalgia or muscle pain, headaches) due to low-grade fever (up to 38º).The temperature increases within 3-5 days and reaches its maximum (40º).The duration of fever for about 2 weeks, sometimes longer.Feature - the lack of effect of antibacterial drugs.The character of the temperature characteristic curve (in the evening a significant rise, in the morning and at lunch - relaxation).Prognostically unfavorable sign is a persistent fever (practically not reduced).By day 5 of illness, patients feel overwhelmed, weakness so pronounced that it is difficult to get out of bed, possible impairment of consciousness.On examination, the patient redness of the face, neck and upper chest, pasty face, sclera vascular injection (the so-called ( "hood syndrome" or cranio-cervical syndrome).

2) in patients affected several groups of lymph nodes ( generalized lymphadenopathy).Lymph nodes are slightly increased in size, however, painful, not fused to each other and the surrounding tissue, the skin over them is not changed.

3) One of the symptoms characteristic of the vast majority of patients with HL Lassa - a defeat throat .This symptom appears on the 3-4 day of illness and is characterized by the appearance of pronounced sore throat, pain when swallowing, dry mouth.On examination, flushing, or redness of the throat with severe boundary of this zone, enlarged tonsils, the appearance on the tonsils, headband, soft palate necrotizing elements grayish color, education may gradually merge, occupying a large area throat.On sores can form grayish fibrinous raids.

4) Another frequent syndrome of Lassa Fever - gastroenteritis syndrome .By day 5 of illness, patients complain of nausea, vomiting, epigastric pain (stomach), dissolution of the chair until watery.With a strong expression can become dehydrated, the first sign of which may be thirst, dry mouth, followed by loss of skin tone, blue skin and subsequently lowering blood pressure, decreased urine output and convulsive muscle twitching.

5) By the end of the first week of symptoms may appear hemorrhagic syndrome - rash - a rash on the hemorrhagic body (from the point of petechiae to large ecchymosis).In some cases, it appears and morbilliform rash (mottled papulleznaya).

GL Lassa, DIC

6) In severe cases to the above symptoms and syndromes join
complications that manifest themselves by an average of 9-11 hours of onset:
- pneumonia, and swellinglung (cough, chest pain, coughing, and then while breathing, shortness of breath, when viewed from the dry and wet wheezing, shortening of percussion sound, X-ray revealed infiltrative changes, pleural effusion);
- toxic myocardial damage (slowing of heart rate, or bradycardia, dicrotism heartbeat or pulse wave splitting in the measurement, when arisen myocarditis pulse becomes frequent - tachycardia, and during the inspection - muted tones of the heart, lowering blood pressure);
- liver toxicity (enlarged liver, pain in the right upper quadrant, the change in laboratory parameters), toxic kidney injury (acute renal failure);
- toxic shock (at the height of the fever a rapid fall in blood pressure, cyanosis, or bluish skin, decreased urine output);
- infectious-toxic encephalopathy (swelling of the brain);
- severe manifestations of thrombo-hemorrhagic syndrome (intestinal or uterine bleeding, bleeding in the adrenal glands, bleeding in the myocardium, brain).

Each complication can lead to death in a patient with severe Lassa fever.
lethal outcome occurs 7-14 days after the onset of the disease in 40% of patients (average figure).
With a favorable outcome of the complaint concerned a patient during 3-4 weeks.In the case of recovery of the patient to 1.5 weeks bothers subfebrilitet (mild fever, fatigue or weakness and fatigue, increased cases of hair loss are described).

Diagnosis Lassa fever

preliminary diagnosis is based on:

1) epidemiological history (presence of natural focus of infection, contact with the local people, contact with rodents, exposure to febrile patients, stay in an endemic area within 21 days before the emergence of the disease).
2) Clinical data (a combination of fever, necrotizing ulcerative pharyngitis, gastroenteritis, haemorrhagic manifestations and rash syndrome).
3) the differential diagnosis, which is carried out with a different etiology gemorragiicheskimi fevers (Ebola, Marburg, yellow fever), throat diphtheria, streptococcal sore throat, gastroenteritis other etiology, HFRS, sepsis, malaria, measles, typhoid and others.

final diagnosis is by laboratory data:

1) Non-specific tests: complete blood count (leukopenia, leukocytosis, and then, decreased platelet count, increased ESR up to 50-80 mm / h), a decrease in blood clotting, biochemistry (increaseALT, AST, GGT, decreased prothrombin, albumin), general analysis of urine (proteinuria, red blood cells, cylinders) and others.
2) Specific studies (carried out in special laboratories for working with infectious agents I hazard class).The materials for research are nasopharyngeal swabs, blood, urine and other, climbed during the first 2 weeks of illness.Materials are collected in sterile containers, are packed, labeled and in metal Bix sent to the laboratory with the accompanying.For diagnosis using a biological method, serological tests for the detection of antigen and antibody (IFA RNIF- rapid diagnosis of Lassa virus antigen, IHA, RSK - the identification of antibodies).If a 2m weeks of onset of the acute phase antibodies - IgM are absent, then the diagnosis is in doubt.According to WHO recommendations diagnostic titer of IgG antibody titer is 1: 512.

Lassa Fever Treatment

1. Organizational regime activities include absolute hospitalization of suspected Lassa GL.All caregivers should work in personal protective equipment (Anti suit type 1 and its modern version).Diet is directed to a mechanical, chemical shchazhenie patient's body, but is adjusted depending on the leading syndrome.

2. options specific therapy. While working on specific outbreaks therapy serum or plasma has been proposed for the infection recover from GL Lassa in an amount of 250-500 ml dose, which should be taken no earlier than 2 months after recovery.It has also been proposed as an alternative therapy scheme ribavirin, interferon reception inhalation.All specific therapy can be successful in the first 6 days of onset.

3. pathogenetic therapy involves detoxification (intravenous infusion of glucose-salt mixtures, carrying out forced diuresis), glucocorticoids, prevention and treatment of DIC up to the transfusion of blood products, rehydration (fluid replacement) during dehydration, drugs that improvethe blood supply to organs and systems, gepatoprotektory, vitamin therapy and others.

4. Posindromalnaya therapy (with pharyngitis - a topical treatment with gastroenteritis - chelators, intestinal antiseptics, probiotics), and others.

GL Lassa, work with patients

At congenial disease patients discharged after clinical recovery, but the disability sheets extend to 4-6 weeks.Clinical examination is not shown except for residual effects.

Prevention of Lassa fever

- Timely detection of patients with fever and rapid isolation of infectious hospitals in boxes.Isolation of individual dishes and individual household supplies.The duration of isolation - not less than 30 days from the onset of the disease.
- Job service personnel patients and staff of laboratories for research in a special protective clothing.
- Identifying contacts and quarantined for 21 days (temperature measurement, inspection of the contact), and with the appearance of symptoms - special insulation.
- Emergency prevention comprises administering ribavirin 800 mg / day for 10 days.
- event in the outbreak: cremation or burial of the dead after dez.obrabotki, burning things dead.
- the current and final disinfection in the outbreak of Lassa GL with special disinfectants.
- Specific prevention absent.
- The fight against rodents in populated areas (the elimination of landfills, timely repair of dwellings, improvement of social conditions of the population).Carrying out disinfestation in the hearth.
- Information work with a population of endemic foci.

infectious disease doctor Bykov NI