Measles Virus

Measles virus is the causing agent for the disease. He is present in the sick man’s blood and respiratory and nasal secretions and in the rash’s elements. The measles virus is not present in healthy persons, because there are no human carriers with inactive measles virus.

Isolation of measles virus was done on tissue culture (human kidney, or monkey), using blood or pharyngeal secretions from patients suffering from measles.

Morphology-measles virus is a spherical particle of 120 – 128?m in diameter, with small surface projections acicular. Structurally, it contains a nucleon capsule, the RNA and an outer sheath composed of lipids, glycoprotein and polypeptides. Infectivity is related to the skin. Antigen for complement fixation is present in the nucleon capsule, and specifically stated are given coating. Unlike other related viruses, measles virus does not possess neuraminidase. There is only one antigenic type.

Resistance in the external environment and physical factors-measles virus is least resistant to the external environment, especially at high temperatures. It lasts for a few weeks in the refrigerator and several months in a frozen state at 790 C. From 150 to 370 degrees C loses half of infectivity within 2 hours. In a room with normal temperature and low humidity, resists better, but loses 50-70% of infectivity in conditions of high humidity. It is quickly destroyed by radiation. The exposure to formalin (1 / 4000) for 4 days to 370, results in virus inactivation (complete loss of infectivity). Measles virus is sensitive to any antibiotic.

The measles virus enters the human’s body through the nasal and eye mucosa. Some authors have argued that the gate would only virus eye mucosa (children receptive to the measles, brought into contact with patients suffering from measles, the disease did not, if they were applied to glasses, covering the entire orbital region or if they convalescent serum ).

After penetration through the mucosal, the virus reaches the lymphoid tissue, where it multiplies (incubation period). The virus could be isolated from blood during this period. When he made the maximum number of multiplication the measles virus invades the blood and organs, causing the first symptoms of disease. Measles virus during this period isolates itself in the blood, nasal secretions and urine. In blood, measles virus is located mainly in leukocytes where it multiplies (which would explain the leucopenia and frequent changes measles cromozoms).

During measles, immunological and metabolic changes are committed. Thus, in severe forms of measles an important immune suppression has been observed (especially cellular immunity), showing a decrease in the number of T lymphocyte, and a decreased resistance to bacterial infection.

Severe measles is often encountered in the tropics, it is accompanied by a more prolonged elimination of measles virus and prolonged presence of giant cell (8-29 days), compared with an average period of 6 days in ordinary measles. It is believed that this gravity is due to a strong cellular immunity depression, in children with malnutrition, which would promote viral proliferation and disease severity.

The disease ceases when neutralizing antibodies appear, which increase gradually, reaching the maximum between the 7th and 10th days of convalescence. The numbers of these antibodies remain high, even after a year and then it persists throughout life and providing immunity against measles.

Positive diagnosis of measles is generally easy. For this we use epidemiological data (lack of history of measles, contact 10 -12 days before infection), clinical signs (eye-respiratory catarrh intense, “cry-baby” face, sign Koplik, rash) and laboratory data (leucopenia) . Cytological examination of nasal secretion which reveal giant cells, multinucleated characteristic for measles, have diagnostic value especially during the pre erupting stage of the disease.

Isolation of the measles virus is not a usual method of diagnosis. Serological reactions, allowing a diagnosis, highlighting the presence and antibodies are: complement fixation, neutralization reaction.

Differential diagnosis: in the pre eruptive stage measles may be confused with various viral respiratory infections (flue, colds), which must be distinguished by epidemiological history.

Measles is a highly prevalent disease (over 90% of the disease appears to the unvaccinated population in adulthood). In developing countries (low level life conditions and poor hygiene), measles is accompanied by a high mortality (12% or more) in other countries, the risk is much lower (mortality 0.02-0,1%).