Parvovírus B19

Classificação

Características Gerais

Estrutura

• Família Parvoviridae Parvoviridae A family of very small DNA viruses containing a single molecule of single-stranded DNA and consisting of two subfamilies: parvovirinae and densovirinae. They infect both vertebrates and invertebrates. Parvovirus B19
• Género Eritroparvovírus
• Sem envelope Envelope Bilayer lipid membrane acquired by viral particles during viral morphogenesis. Although the lipids of the viral envelope are host derived, various virus-encoded integral membrane proteins, i.e. Viral envelope proteins are incorporated there. Virology, cápside icosaédrica e genoma de DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure linear de cadeia simples
• Muito pequeno: aproximadamente 22-24 nm de diâmetro

Principais características

• Descoberto em 1974
• Incapaz de propagar vírus em culturas de células
• Tropismo único por células progenitoras eritroides humanas

Epidemiologia e Patogénese

Epidemiologia

• A infeção ocorre em todas as idades, mas é mais MAIS Androgen Insensitivity Syndrome comum em crianças dos 3 aos 15 anos de idade.
• Os surtos ocorrem geralmente em escolas e creches e são mais MAIS Androgen Insensitivity Syndrome frequentes entre o final do inverno e o início do verão.
• 90% dos pacientes ≥ 60 anos são seropositivos.

Patogénese

• Reservatórios:
  • As parvoviroses causam doenças em animais e insetos.
  • O B19 é o único agente patogénico de parvovírus humano.
• Transmissão:
  • Gotículas respiratórias infetadas
  • Sangue
  • O risco de contágio secundário em membros da família expostos é de 50% e em contactos em sala de aula é de 25%.
• Ciclo de vida do B19: O vírus liga-se aos recetores da célula hospedeira → endocitose → translocação do genoma para o núcleo hospedeiro → replicação do DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure → transcrição do RNA RNA A polynucleotide consisting essentially of chains with a repeating backbone of phosphate and ribose units to which nitrogenous bases are attached. RNA is unique among biological macromolecules in that it can encode genetic information, serve as an abundant structural component of cells, and also possesses catalytic activity. RNA Types and Structure → montagem da cápside e empacotamento do genoma → lise celular com libertação de viriões maduros

Fisiopatologia

• Infeção inicial com B19 no local de entrada (frequentemente no trato respiratório superior) → o vírus propaga-se para as células precursoras eritroides em divisão rápida na medula óssea, que expressam um antigénio sanguíneo P
• Uma vez dentro da célula hospedeira, o DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure viral entra no núcleo → o vírus é citotóxico para as células → ↓ eritrogénese:
  • O agente B19 requer um recetor de antigénio do sangue P para entrar na célula.
  • Os indivíduos raros que não possuem antigénio P são imunes.

Doenças Causadas pelo Parvovírus B19

Pacientes saudáveis

• Eritema infecioso (5ª doença): doença bifásica que ocorre principalmente em crianças
  • Fase inicial:
    • Representa a infeção lítica
    • Marcada por sintomas inespecíficos semelhantes aos da gripe
    • ↓ Níveis de hemoglobina
  • Fase imunomediada:
    • Começa 2-3 semanas depois
    • Caracterizada por uma erupção cutânea e artralgias: a “erupção bofetada na bochecha” aparece primeiro no rosto → propaga-se para os membros superiores e inferiores
  • O diagnóstico é normalmente baseado na apresentação clínica; nas apresentações atípicas o diagnóstico pode ser sustentado com o teste de anticorpos IgG IgG The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of igg, for example, igg1, igg2a, and igg2b. Hypersensitivity Pneumonitis e IgM IgM A class of immunoglobulin bearing mu chains (immunoglobulin mu-chains). Igm can fix complement. The name comes from its high molecular weight and originally being called a macroglobulin. Immunoglobulins: Types and Functions por ELISA ELISA An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed. St. Louis Encephalitis Virus.
  • Tratamento: doença autolimitada que requer apenas tratamento de suporte
• A síndrome de poliartropatia em adultos pode não ser precedida por erupção cutânea.
  • Artralgias agudas e simétricas
  • Envolve sobretudo pés, joelhos, mãos e punhos
  • Sem danos articulares duradouros
  • Doença autolimitada; resolve em 3 semanas
  • Tratamento: sintomático, com analgesia Analgesia Methods of pain relief that may be used with or in place of analgesics. Anesthesiology: History and Basic Concepts (AINEs) e cuidados de suporte

Doentes imunodeprimidos

Aplasia Aplasia Cranial Nerve Palsies eritrocitária pura:

• Não é possível erradicar infeções por parvovírus B19 → aplasia Aplasia Cranial Nerve Palsies de hemácias e dos seus precursores consequente
• Pode não haver sinais clássicos de infeção
• Causa anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types crónica
• Pode ser fatal
• Diagnóstico: PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR) para detetar o DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure do parvovírus B19.
• Tratamento:
  • Tem como objetivo minimizar a imunossupressão, se possível (por exemplo, reduzir a dosagem de quimioterapia)
  • Tratamento com imunoglobulina intravenosa (IGIV)
  • Em casos graves, transplante de medula óssea

Pacientes com hemoglobinopatias

A crise aplásica transitória pode ocorrer em indivíduos com hemoglobinopatias (por exemplo, anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types falciforme):

• A reticulocitopenia transitória (7–10 dias) leva à ↓ dos níveis de hemoglobina.
• Os sintomas incluem:
  • Febre
  • Mal-estar
  • Prurido
  • Arrepios
  • Artralgias
  • Erupção cutânea maculopapular Maculopapular Dermatologic Examination
• Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types
• Geralmente resolve em semanas
• Tratamento: transfusão para hemoglobina < 6 g/dl com reticulopenia

Mulheres grávidas

• Hidrópsia fetal:
  • Corresponde à acumulação anormal de líquido nos tecidos moles Moles Primary Skin Lesions fetais
  • Os mecanismos ainda não estão totalmente esclarecidos, mas pensa-se que esteja relacionada com a anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types aguda causada pelo vírus: a diminuição do número de hemácias e o aumento da necessidade de volume circulante levam à retenção de líquidos.
  • Associada a aumento do risco de hidrópsia fetal
  • Tratamento: 
    • Transfusão intrauterina
    • Tratamento com IGIV
    • Entubação/suporte ventilatório pós-natal e fluidoterapia
• Morte fetal no útero:
  • Risco ↑ quanto mais MAIS Androgen Insensitivity Syndrome cedo a infeção for contraída durante a gestação.
  • O sistema imune fetal imaturo é menos capaz de reagir à infeção.
• Anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types congénita:
  • A renovação de hemácias fetal é mais MAIS Androgen Insensitivity Syndrome rápida do que na vida pós-natal.
  • Torna o feto mais MAIS Androgen Insensitivity Syndrome suscetível à anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types
• O envolvimento do parvovírus é confirmado através de testes Testes Gonadal Hormones de anticorpos IgG IgG The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of igg, for example, igg1, igg2a, and igg2b. Hypersensitivity Pneumonitis e IgM IgM A class of immunoglobulin bearing mu chains (immunoglobulin mu-chains). Igm can fix complement. The name comes from its high molecular weight and originally being called a macroglobulin. Immunoglobulins: Types and Functions por ELISA ELISA An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed. St. Louis Encephalitis Virus.

Comparação de Erupções Cutâneas Comuns na Infância