Retroviral infections
Retroviral infections are diseases caused by retroviruses, which are RNA-based viruses capable of integrating their genetic material into host cells. These infections can lead to various health issues, including malignancies, immunodeficiencies, and neurological disorders. Human immunodeficiency virus (HIV), the virus responsible for acquired immunodeficiency syndrome (AIDS), is one of the most well-known retroviruses. Transmission occurs primarily through the exchange of fluids, such as during sexual contact, blood transfusions, or from mother to child during childbirth.
Symptoms of retroviral infections often stem from the compromised function of host cells and may include chronic fatigue, weight loss, fever, night sweats, and pain. Diagnosis typically involves detecting antibodies specific to the virus through blood tests, with newer methods using oral secretions or urine tests also available. While antiviral therapy can help manage these infections, there is currently no cure, and ongoing treatment is required to control the viral load.
Preventive measures focus on minimizing exposure to the virus, particularly through safe sexual practices and cautious handling of blood products, as no vaccine exists to provide immunity against retroviral infections. Understanding these aspects is crucial for managing health risks associated with retroviral diseases.
Retroviral infections
Anatomy or system affected: All
Definition
A retroviral infection is a disease state caused by a retrovirus that incorporates into a host cell. A retrovirus is composed of ribonucleic acid (RNA) that has the ability to replicate itself in a host cell. Retroviruses are associated with a variety of diseases, including malignancies, immunodeficiencies, and neurologic disorders.
There are seven genera of retroviruses divided into two categories, simple and complex. Perhaps the best known retrovirus is human immunodeficiency virus (HIV), which is the virus that causes acquired immunodeficiency syndrome (AIDS). Other examples of common retroviruses include human T-cell leukemia virus, Raus sarcoma virus in chickens, and murine and feline leukemia viruses in mice and cats. Retroviruses also exist among other host species, ranging from plants to invertebrates, fish, birds, and many mammalian species.
Causes
The cause of an infection in general is the detrimental colonization of a host organism by a foreign pathogenic species. These foreign organisms can interfere with the normal functioning of the host cell, which can lead to chronic wounds, illness, and death.
More specifically, viral infections, for example, are caused by viral particles, which are not considered organisms because they lack metabolism and reproduction (when no host cell is present). In the case of a retroviral infection, the genome carried by a virus is RNA, which can be used directly as messenger RNA to convert the coded message into viral proteins that have specific functions.
One specific protein produced by the retrovirus is the enzyme known as reverse transcriptase, which can then be used to convert RNA into a deoxyribonucleic acid (DNA) molecule. This new DNA molecule is then used to produce more genetic material for new viral particles; it can also incorporate its genetic material in the host cell’s genome. These new viruses can remain in the host cell’s genome for long periods, without causing disease. However, the viruses are continuously copying the viral genome in the host. At some point, the viral particles leave this quiescent stage and become pathogenic, causing a disease state.
Risk Factors
Because retroviral infection in humans is caused by the incorporation of viral particles into a human host cell, the risk factor for this type of infection is exhibited by the secretion of fluids containing the virus from one person to another. The primary factors contributing to this spread of viral particles include transmission through sexual intercourse, blood transfusion, or contaminated needles, and transmission by a woman to her fetus or newborn.
Sexual activity is the most widely known transmission factor for HIV infection. Chronic retroviral infection, also common, involves a primary infection that can lead to recurring infections. Once retroviruses are incorporated into host cells, the host immune system is compromised, which further exasperates the risk of future infections. Thus, low immune response has been a major factor in developing a high risk for chronic retroviral disease.
Symptoms
Because of the severe weakening of the normal functioning host cell after retroviral infection, most symptoms reflect the loss of function of these cells. These symptoms include chronic fatigue, continuous weight loss, low-grade or spiking fever, night sweats and chills, and chronic body aches and pain. These are somewhat vague symptoms, but they reflect the reach of how a host’s normal functioning cells become impaired (compromised); these wide-ranging symptoms also reflect the lack of a proper immune response to eradicate the retrovirus from the body. Typically, retroviral infections are systemic, involving many different parts of the body; therefore, symptoms tend to include many organ systems. As the body weakens, symptoms become more severe.
Screening and Diagnosis
Infection by a retrovirus is generally detected by the presence of specific antibodies to the virus, because antibodies to viruses persist for life. Screening from blood or blood products using the enzyme-linked immunosorbent assays (ELISA) are generally used for diagnosis. A positive serum level that is found repeatedly by ELISA screening is then further tested to confirm the presence of specific antibodies.
Screening for HIV infection, in particular, is most commonly done by collecting secretions from between the cheek and gum and then evaluating them for HIV antibodies. This test is nearly as accurate as a blood test, and because it does not involve a needle stick, it is favored by many persons. Finally, a newer urine test is available for screening. However, if the test is positive, blood tests need to be performed to confirm the presence of HIV.
Treatment and Therapy
Antiviral therapy (ART) is the use of drugs to control the retrovirus by interfering with the virus’s invasion of cells and multiplication in the host. Although ART can successfully control a retroviral infection, it is not a cure for the disease; also, ART drugs need to be taken for life to maintain their effect.
The most common ART is that used for AIDS, mainly because the disease is so widespread (global) and because of its fatality rate. The most common form of ART for HIV and AIDS is highly active antiretroviral therapy (HAART), a group of three to four drugs taken in combination.
Different classes of drugs effect different stages of the retroviral life cycle. Nucleoside and nucleotide reverse transcriptase inhibitors block (inhibit) reverse transcription of RNA to DNA in a host cell by preventing the elongation of the DNA molecule. Non-nucleoside reverse transcriptase inhibitors inhibit the virility of retroviruses and cause cell death.
Prevention and Outcomes
The best way to prevent infection by a retrovirus is to avoid contact with that virus. Because one of the most common retroviruses is HIV, mainly transmitted either sexually, through a contaminated needle, or through blood transfusions, the only way to protect against HIV infection is to abstain from sex outside a mutually faithful relationship with a partner whom the person knows is not infected with HIV, to abstain from sharing drug needles, and to be aware of blood transfusion origins. No antiretroviral vaccine exists.
Bibliography
Coffin, J. M., S. H. Hughes, and H. E. Varmus, eds. Retroviruses. Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press, 2002. A good discussion of retroviruses.
Kurth, R., and N. Bannert, eds. Retroviruses: Molecular Biology, Genomics, and Pathogenesis. Norwich, England: Caister Academic Press, 2010. A comprehensive discussion of retroviruses and related infections.
Levy, Jay A. HIV and the Pathogenesis of AIDS. 3d ed. Washington, D.C.: ASM Press, 2007. Provides a review of the research, explains the history of the disease, and examines how scientists, clinicians, and public health workers have responded to HIV and AIDS.
Norkin, Leonard. Virology: Molecular Biology and Pathogenesis. Washington, D.C.: ASM Press, 2010. The author provides a detailed account of virus structure and replication and of the basis for disease pathology.