Human Herpesvirus type 8 (HHV-8):IgM and IgG antibodies; Molecular diagnosis (PCR).
Human herpesvirus 8 (HVH-8), also called Kaposi sarcoma herpesvirus (HVSK), was discovered by Chang et al. in 1994. It is an oncogenic virus associated with Kaposi´s sarcoma (KS) and lymphoproliferative disorders, such as primary lymphoma with effusion and Castleman's disease. The seroprevalence of the virus is different throughout the world, with low frequency in the United States and Northern Europe (1% to 5%), between 10% to 20% in certain Mediterranean countries and 30% to 80% in areas of the Sub-Saharan Africa As with other oncogenic viruses, HHV-8 is a necessary but insufficient cause of malignancy. Seropositivity alone does not predict progression to KS or other diseases. Human immunodeficiency virus (HIV) infection and immunodeficiencies are important risk factors, although the exact triggers that allow HVH-8 to progress to KS or other diseases remain unknown. Although the incidence of Kaposi´s sarcoma has decreased since the application of highly active antiretroviral therapy, this disease continues to be one of the most common malignancies observed in HIV-infected patients.
HVH-8 belongs to the family Herpesviridae, subfamily Gammaherpesvirinae and genus Radhinovirus. It has a marked lymphotropism and, like other members of this group, it is a virus of 120 to 150 nm, covered by a phospholipid membrane that surrounds a nucleocapsid with double stranded DNA, icosahedral symmetry and a complex genetic and antigenic structure. Its known hosts are exclusively humans. This virus is capable of infecting several types of cells, including monocytes, dendritic cells, B lymphocytes, oral epithelial cells and, in KS tumors, endothelial cells. The virus exists in both lytic and latent form and the viral pathogenesis of KS depends on the regulation between these 2 phases. The lytic phase is necessary for the primary infection of a new host. After primary infection, the virus persists in the latent phase with episomal DNA that expresses only some of its genes in 4 open reading frames (ORF). The latent phase virus can be induced to re-enter the lytic state of viral replication, although the triggers of this phase transition are not fully known. The clinical disease is usually due to a chronic infection, but in some cases, especially in organ transplantation, the disease can manifest itself from a primary disseminated lytic infection. Advances in molecular pathology have revealed that HHV-8 tumorigenesis is mediated by molecular mimicry in which virus-encoded proteins can activate several cell signaling cascades while immunological surveillance is evaded.
The mechanisms of transmission of HVH-8 are not clearly defined, but epidemiological and virological data suggest that saliva is a source of infectious virus and may be an important route of transmission. Asymptomatic HHV-8 infection is often associated with the release of HHV-8 in saliva and occasional in genital secretions. According to these observations, the elimination of the virus can cause the transmission of HHV-8 to uninfected couples through behaviors associated with exposure to saliva or genital secretions. In addition, HHV-8 can be transmitted by transfusion of blood and genital organs. Vertical transmission and through breastfeeding are considered to have an unimportant role.
Most people with latent infection with HHV-8 are asymptomatic. Immunocompetent children and recipients of transplants of organs infected with HHV-8 may develop a primary infection syndrome consisting of fever, rash, lymphadenopathy, bone marrow failure and occasional rapid progression to SK. The manifestations of SK vary widely, but most patients have non-sensitive, hyperpigmented, macular or nodular skin lesions. Oral lesions occur in approximately one third of patients and are predictors of pulmonary involvement and less favorable treatment outcomes. Lymphatic involvement is also common and can cause debilitating edema of the lower extremities. Internal organ involvement occurs in up to 50% of cases and can be difficult to diagnose. Patients with visceral involvement may be asymptomatic or manifest with difficulty breathing, painless rectal bleeding and other nonspecific pulmonary and gastrointestinal symptoms.
Lymphoma with primary effusion characteristically presents with isolated effusions within the pleural, pericardial or abdominal cavities, but massive lesions and "extracavitary" disease within the skin, hematopoietic organs and the gastrointestinal tract have been described. Castleman´s disease manifests itself routinely with systemic symptoms, such as fever and night sweats, and exam findings, including generalized adenopathy, fever and hepatosplenomegaly. Castleman´s disease can mimic other inflammatory conditions, including sepsis, with hypotension, clinical evidence of a systemic inflammatory response and progression to multiorganic insufficiency. Another condition associated with this virus has been discovered more recently, the inflammatory cytokine production syndrome associated with HVH-8 (KICS). Patients with this syndrome show inflammatory symptoms similar to Castleman´s disease, but have no pathological findings of that disease. KICS patients are often seriously ill and show high elevations of IL-6 and IL-10, as well as high viral loads of HVH-8 in plasma. KICS may contribute to the inflammatory symptoms observed in some patients with KS or lymphoma with severe primary effusion, and there may be a significant clinical overlap between these conditions.
The laboratory diagnosis of HVH-8 infection is based on direct methods of molecular biology, aimed at detecting the nucleic acid of the virus, and indirect methods based on the demonstration of antibodies against different virus antigens. The use of both diagnostic methods is essential for the epidemiological study of the virus, the clinical management of HIV-infected patients and organ transplantation. However, the diagnosis of KS, lymphoma with primary effusion or Castleman´s disease depends on cytological and immunological cell markers, as well as histopathology. The clinical diagnosis alone is not enough for KS and other pathologies and a tissue test is needed to confirm the diagnosis. Confirmation of these diagnoses is achieved by immunohistochemical staining of tumors with antibodies that recognize the latency-associated nuclear antigen encoded by HVH-8, or by using polymerase chain reaction (PCR) to identify HVH-8 DNA inside the tumor tissue.
Tests performed in IVAMI:
- Molecular diagnosis (PCR) of HVH-8.
- Detection of IgM and/or IgG antibodies by indirect immunofluorescence.
- Molecular diagnosis (PCR) of HVH-8: blood, plasma, serum, saliva, genital secretions or tumors.
- Detection of IgG and/or IgM antibodies against HVH-8 by immunofluorescence: blood (5 mL) or serum (2 mL).
Storage and shipment of the sample:
- Refrigerated (preferred) for less than 2 days.
- Frozen: more than 48 hours.
Note: in case of sending blood for separation of the serum in the laboratory, it must be sent refrigerated (never frozen) in a period less than 48 hours.
Delivery of results:
- Molecular diagnosis of HVH-8: 48 to 72 hours.
- Detection of IgG and/or IgM antibodies against HVH-8: 5 working days.
Cost of the test:
- Molecular diagnosis of HVH-8 by PCR: consult to firstname.lastname@example.org
- Detection of IgM antibodies against HVH-8 by indirect immunofluorescence: consult to email@example.com.
- Detection of IgG antibodies against HVH-8 by indirect immunofluorescence: consult to firstname.lastname@example.org.