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pharmacology

Protected herd

Researcher from the State of Minas Gerais makes a more efficient DNA vaccine against brucellosis, a contagious illness that attacks cattle

There has been an advance in the fight against cattle brucellosis: Sérgio Costa Oliveira of the Biological Sciences Institute of the Federal University of Minas Gerais (UFMG), has developed a DNA (deoxyribonucleic acid, the genetic code carrier) vaccine composed of one or more genes of the bacterium that causes the illness, associated with a viral component – the so-called genetic adjuvant, which powers up the effects of the vaccine and can also serve as an alternative genetic therapy in humans. The discovery has resulted in scientific papers published in the Journal of Virology and Human Gene Therapy.

Caused by the bacterium Brucella abortus , bovine brucellosis brings on abortions in cattle at the start of their fifth month of gestation, jeopardizes their fertility and reduces milk production by up to 25%. In Brazil, close to 8.5 million cattle (5% of the national herd) are contaminated and the annual loss is estimated at around US$ 100 million.

When it is transmitted to a human being, through contact with infected animals or the consumption of contaminated milk or its derivatives, the illness shows itself through an intermittent fever, which, – if not treated with antibiotics – can lead to inflammation of the bones, heart and other organs. No vaccine exists for human use.

The vaccine most widely used in Brazil against the disease is B19, produced from live micro organisms. Although it has an efficiency of 70%, there are limitations. It can only be applied to cows from three to eight months and can confuse the diagnosis: in the serological examination that detects anti-bodies that act against the disease, it is difficult to know if it is in the animal because it was vaccinated or because it is ill. On the other hand, the genetic vaccine, in the opinion of Oliveira, can be applied at any age, both to cows and oxen s – since it is a disease linked to reproduction, the males can contaminate themselves with the females and contaminate the entire herd. The efficiency, confirmed during a year of tests on one hundred and fifty mice, was of almost 70%.

Oliveira points to other advantages: “The large scale production is cheaper, the maintenance of quality control is easier and there is not the need for refrigeration to store the vaccine that remains stable at room temperature”. Disadvantages? There is the potential risk of a DNA vaccine integrating itself into the genome of the cell, animal or human, and generating a mutation that could activate genes that, for example, cause cancer or inhibit tumor suppressing genes. The UFMG researcher discards this possibility, citing studies carried out at the Merck Laboratory in the United States, according to which the frequency of normal cellular mutation is greater that that occasionally induced by vaccination with DNA.

Protein messenger
Previously, during his post doctorate study on cellular and molecular immunology at Wisconsin University in the United States, Oliveira had worked on vaccines against brucellosis. Basing itself on the principle that genetic immunization is similar to a viral infection, in which the virus needs to reach the nucleus of the cell, he decided to incorporate a component of the virus.

In the tegument of the herpes virus, an illness that also affects cattle, he described the protein VP22, which is fundamental in the molecules traffic between the cells and moves itself easily to the nucleus of the host cell. Consequently, its function as a genetic adjuvant – integrated into the target gene of the vaccine – is to transport the antigen – the gene that produces antibodies against brucellosis – for different cells. The adjuvant multiplies the reactions: increases the response of the antibody for the codified protein by the geneo f the interest of the vaccine and augments the cellular response measured by the T lymphocytes, a type of cell of the immunological system.

Oliveira has had to leave the laboratory and go in search of financing through research support agencies, as well as partnerships with private companies in order to make possible the next stage of the research: to carry out tests on at least fifty cattle over the period of one year.

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