Human cytomegalovirus | |
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Specialty | Infectious disease |
Causes | Human betaherpesvirus 5 |
Human betaherpesvirus 5 | |
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CMV infection of a human lung pneumocyte | |
Virus classification | |
(unranked): | Virus |
Realm: | Duplodnaviria |
Kingdom: | Heunggongvirae |
Phylum: | Peploviricota |
Class: | Herviviricetes |
Order: | Herpesvirales |
Family: | Orthoherpesviridae |
Genus: | Cytomegalovirus |
Species: | Human betaherpesvirus 5 |
Synonyms [1] | |
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Human betaherpesvirus 5, also called human cytomegalovirus (HCMV,HHV-5), [2] is a species of virus in the genus Cytomegalovirus , which in turn is a member of the viral family known as Herpesviridae or herpesviruses. It is also commonly called CMV. [3] Within Herpesviridae , HCMV belongs to the Betaherpesvirinae subfamily, which also includes cytomegaloviruses from other mammals. [4] CMV is a double-stranded DNA virus. [5]
Although they may be found throughout the body, HCMV infections are frequently associated with the salivary glands. [4] HCMV infection is typically unnoticed in healthy people, but can be life-threatening for the immunocompromised, such as HIV-infected persons, organ transplant recipients, or newborn infants. [3] Congenital cytomegalovirus infection can lead to significant morbidity and even death. After infection, HCMV remains latent within the body throughout life and can be reactivated at any time. Eventually, it may cause mucoepidermoid carcinoma and possibly other malignancies [6] such as prostate cancer, [7] [8] breast cancer, [9] ovarian cancer [10] and glioblastoma. [11] [12]
HCMV is found in all geographic locations and all socioeconomic groups, and infects between 60% and 70% of adults in the first world and almost 100% in the third world. [13] Of all herpes viruses, HCMV harbors the most genes dedicated to altering (evading) innate and adaptive host immunity and represents a lifelong burden of antigenic T cell surveillance and immune dysfunction. [14] Commonly it is indicated by the presence of antibodies in the general population. [3] Seroprevalence is age-dependent: 58.9% of individuals aged 6 and older are infected with CMV while 90.8% of individuals aged 80 and older are positive for HCMV. [15] HCMV is also the virus most frequently transmitted to a developing fetus. [16] HCMV infection is more widespread in developing countries and in communities with lower socioeconomic status and represents the most significant viral cause of birth defects in industrialized countries. Congenital HCMV is the leading infectious cause of deafness, learning disabilities, and intellectual disability in children. [17] CMV also "seems to have a large impact on immune parameters in later life and may contribute to increased morbidity and eventual mortality." [18]
Human betaherpesvirus 5 infection has a classic triad of symptoms: fever, peaking in the late afternoon or early evening; pharyngitis, usually exudative; and symmetrical adenopathy. [19] [20] [21]
The mode of HCMV transmission from person to person is unknown, but is presumed to occur through bodily fluids, including saliva, urine, blood, and tears. [22] Cytomegalovirus is most commonly transmitted through kissing and sexual intercourse. It can also be transferred from an infected mother to her unborn child. [4] Infection requires close, intimate contact with a person secreting the virus in their saliva, urine, or other bodily fluids. CMV can be transmitted sexually and via breast milk, and also occurs through receiving transplanted organs or blood transfusions. [23] Although HCMV is not highly contagious, it has been shown to spread in households and among young children in day care centers. [3]
HCMV replicates within infected endothelial cells [24] at a slow rate, taking about five days in cell culture. [25] It also infects fibroblasts, which requires expression of only a trimeric viral receptor complex, rather than the full pentameric complex that is required for infection of endothelial and epithelial cells. [26] Like other herpesviruses, HCMV expresses genes in a temporally controlled manner. [27] [28] Immediate early genes (expressed 0–4 hours after infection) are involved in the regulation of transcription, followed by early genes (expressed 4–48 hours after infection) which are involved in viral DNA replication and further transcriptional regulation. [27] Late genes are expressed during the remainder of infection up to viral egress and typically code for structural proteins. While HCMV encodes for its own functional DNA polymerase, the virus makes use of the host RNA polymerase for the transcription of all of its genes. [29]
In disseminated cytomegalovirus infections, as may be seen in the context of an immunosuppressed host, the virus is readily transmitted between polymorphonuclear leukocytes (PM-NLs) and endothelial cells. Infected endothelial cells produce cytokines that attract PM-NLs, which then adhere to the endothelium by interactions between their CD18-containing cell surface integrins and the endothelial-expressed ICAM-1. Microfusions between the cells then take place in a manner dependent on expression of the viral gene locus UL128L. [26]
Synthesis of the viral double-stranded DNA genome occurs at the host cell nucleus within specialized viral replication compartments. [30]
Nearly 75% of the genes encoded by HCMV strain AD169 can be deleted and still result in the production of infectious virus. [31] This suggests that the virus focuses on avoiding the host immune system for a timely entrance into latency. [32]
CMV infections are most significant in the perinatal period and in people who are immunocompromised.
HCMV is one of the vertically transmitted infections that lead to congenital abnormalities. (Others are: toxoplasmosis, rubella and herpes simplex.) Congenital HCMV infection occurs when the mother has a primary infection during pregnancy. [33] [34] [35]
Up to 5 of every 1,000 live births are infected. Five percent develop multiple handicaps, and develop cytomegalic inclusion disease with nonspecific signs that resemble rubella. Another five percent later develop cerebral calcification (decreasing IQ levels dramatically and causing sensorineural deafness and psychomotor retardation).[ citation needed ]
However, infants born preterm and infected with HCMV after birth may experience cognitive and motor impairments later in life. [36]
CMV infection or reactivation in people whose immune systems are compromised—for example people who have received transplants or are significantly burned—causes illness and increases the risk of death. [37] [38]
CMV reactivation is commonly seen in people with severe colitis. [39]
Specific disease entities recognized in those people are
People without CMV infection who are given organ transplants from CMV-infected donors require prophylactic treatment with valganciclovir (ideally) or ganciclovir, and regular serological monitoring to detect a rising CMV titre; if treated early establishment of a potentially life-threatening infection can be prevented. [41]
CMV infections can still be of clinical significance in adult immunocompetent populations. [42]
The question of whether latent CMV infection has any negative effects on people who are otherwise healthy has been debated; as of 2016 the answer was not clear, but discussions had focused on whether latent CMV might increase the risk of some cardiovascular diseases and cancers. [37]
Most healthy people who are infected by HCMV after birth have no symptoms. [3] Some develop a syndrome similar to infectious mononucleosis or glandular fever, [47] with prolonged fever, and a mild hepatitis. A sore throat is common. After infection, the virus remains latent in lymphocytes in the body for the rest of the person's life. Overt disease rarely occurs unless immunity is suppressed either by drugs, infection or old age. Initial HCMV infection, which often is asymptomatic, is followed by a prolonged, inapparent infection during which the virus resides in mononuclear cells without causing detectable damage or clinical illness. [48]
Infectious CMV may be shed in the bodily fluids of any infected person, and can be found in urine, saliva, blood, tears, semen, and breast milk. The shedding of virus can occur intermittently, without any detectable signs or symptoms.
CMV infection can be demonstrated microscopically by the detection of intranuclear inclusion bodies. On H&E staining, the inclusion bodies stain dark pink and are called "owl's eye" inclusion bodies. [49]
HCMV infection is important to certain high-risk groups. [50] Major areas of risk of infection include pre-natal or postnatal infants and immunocompromised individuals, such as organ transplant recipients, persons with leukemia, or those infected with human immunodeficiency virus (HIV). In HIV infected persons, HCMV is considered an AIDS-defining infection, indicating that the T-cell count has dropped to low levels.
Lytically replicating viruses disrupt the cytoskeleton, causing massive cell enlargement, which is the source of the virus' name.
A study published in 2009 links infection with CMV to high blood pressure in mice, and suggests that the result of CMV infection of blood vessel endothelium in humans is a major cause of atherosclerosis. [51] Researchers also found that when the cells were infected with CMV, they created renin, a protein known to contribute to high blood pressure.
Human CMV causes cellular senescence, which could contribute to chronic inflammation (inflammaging). [52] Human CMV is also linked to age-associated T cell dysfunction, contributing to immunosenescence. [52] In persons infected with CMV about 10% of memory T cells are CMV-specific, but these may expand to as much as 30% in the elderly, [53] 50% or more of CD8 + memory T-cells. [54] COVID-19 symptom severity is associated with CMV, although the exact mechanism has not been elucidated. [55]
CMV encodes a protein, UL16, which is involved in the immune evasion of NK cell responses. It binds to ligands ULBP1, ULBP2 and MICB of NK cell activating receptor NKG2D, which prevents their surface expression. These ligands are normally upregulated in times of cellular stress, such as in viral infection, and by preventing their upregulation, CMV can prevent its host cell from dying due to NK cells [56]
A substantial portion of the immune system is involved in continuously controlling CMV, which drains the resources of the immune system. [57] [58] Death rates from infectious disease accelerate with age, [59] and CMV infection correlates with reduced effectiveness of vaccination. [60] Persons with the highest levels of CMV antibodies have a much higher risk of death from all causes compared with persons having few or no antibodies. [61] [62]
Most infections with CMV go undiagnosed, as the virus usually produces few, if any, symptoms and tends to reactivate intermittently without symptoms. Persons who have been infected with CMV develop antibodies to the virus, which persist in the body for the lifetime of that individual. A number of laboratory tests that detect these antibodies to CMV have been developed to determine if infection has occurred and are widely available from commercial laboratories. In addition, the virus can be cultured from specimens obtained from urine, throat swabs, bronchial lavages and tissue samples to detect active infection. Both qualitative and quantitative polymerase chain reaction (PCR) testing for CMV are available as well, allowing physicians to monitor the viral load of people infected with CMV.
The CMV pp65 antigenemia test is an immunofluorescence-based assay which utilizes an indirect immunofluorescence technique for identifying the pp65 protein of cytomegalovirus in peripheral blood leukocytes. [63] The CMV pp65 assay is widely used for monitoring CMV infection and its response to antiviral treatment in people who are under immunosuppressive therapy and have had renal transplantation surgery, as the antigenemia results are obtained about 5 days before the onset of symptomatic CMV disease. The advantage of this assay is the rapidity in providing results in a few hours and that the pp65 antigen determination represents a useful criterion for the physician to initiate antiviral therapy. The major disadvantage of the pp65 assay is that only a limited number of samples can be processed per test batch.
CMV should be suspected if a person has symptoms of infectious mononucleosis but has negative test results for mononucleosis and Epstein–Barr virus, or if they show signs of hepatitis, but have negative test results for hepatitis A, B, and C.
For best diagnostic results, laboratory tests for CMV antibody should be performed by using paired serum samples. One blood sample should be taken upon suspicion of CMV, and another one taken within 2 weeks. A virus culture can be performed any time the person is symptomatic. Laboratory testing for antibodies to CMV can be performed to determine if a woman has already had CMV infection. However, routine testing of all pregnant women is costly and the need for testing should therefore be evaluated on a case-by-case basis.
The enzyme-linked immunosorbent assay (or ELISA) is the most commonly available serologic test for measuring antibody to CMV. The result can be used to determine if acute infection, prior infection, or passively acquired maternal antibody in an infant is present. Other tests include various fluorescence assays, indirect hemagglutination, (PCR) and latex agglutination. [64] [65]
An ELISA technique for CMV-specific IgM is available, but may give false-positive results unless steps are taken to remove rheumatoid factor or most of the IgG antibody before the serum sample is tested. Because CMV-specific IgM may be produced in low levels in reactivated CMV infection, its presence is not always indicative of primary infection. Only virus recovered from a target organ, such as the lung, provides unequivocal evidence that the current illness is caused by acquired CMV infection. If serologic tests detect a positive or high titer of IgG, this result should not automatically be interpreted to mean that active CMV infection is present. Active CMV infection is considered to be present if antibody tests of paired serum samples show a fourfold rise in IgG antibody and a significant level of IgM antibody (equal to at least 30% of the IgG value), or if virus is cultured from a urine or throat specimen.[ citation needed ]
Although the risks discussed above are generally low, CMV assays are part of the standard screening for non-directed blood donation (donations not specified for a particular person) in the U.S., the UK and many other countries. CMV-negative donations are then earmarked for transfusion to infants or people who are immunocompromised. Some blood donation centers maintain lists of donors whose blood is CMV negative due to special demands. [66]
During allogeneic hematopoietic stem cell transplant, it is generally advised to match the serostatus of donor and recipient. If the recipient is seronegative, a seropositive donor carries a risk of de novo infection. Conversely, a seropositive recipient is at risk of viral reactivation if they receive a transplant from a seronegative donor, losing their innate defenses in the process. In general, the risk is highest for CMV seropositive recipients, in which viral reactivation is a cause of significant morbidity. For these reasons, CMV serologic testing is routine for both bone marrow donors and recipients. [67] [68]
A phase 2 study of a CMV-vaccine published in 2009 indicated an efficacy of 50%—the protection provided was limited, and a number of subjects contracted CMV infection despite vaccination. In one case also congenital CMV was encountered. [69]
In 2013, Astellas Pharma started on individuals who received a hematopoietic stem cell transplant a phase 3 trial with its CMV deoxyribonucleic acid DNA cytomegalovirus vaccine ASP0113. [70]
In 2015, Astellas Pharma commenced on healthy volunteers a phase 1 trial with its cytomegalovirus vaccine ASP0113. [71]
Further cytomegalovirus vaccines candidates are the CMV-MVA Triplex vaccine and the CMVpp65-A*0201 peptide vaccine. Both vaccine candidates are sponsored by the City of Hope National Medical Center. As of 2016, the development is in clinical phase 2 trial stage. [72] [73]
The Centers for Disease Control and Prevention (CDC) recommend regular hand washing, [74] especially after changing diapers. [75] Hand washing is also recommended after feeding a child, wiping a child's nose or mouth, or handling children's toys. [76]
Hyperimmune globulin enriched for CMV (CMV-IGIV) is an immunoglobulin G (IgG) containing a standardized number of antibodies to cytomegalovirus. It may be used for the prophylaxis of cytomegalovirus disease associated with transplantation of kidney, lung, liver, pancreas, and heart. Alone or in combination with an antiviral agent, it has been shown to:
Ganciclovir (Cytovene) treatment is used for people with depressed immunity who have either sight-related or life-threatening illnesses. Valganciclovir (Valcyte) is an antiviral drug that is also effective and is given orally: it is a pro-drug that gets converted into ganciclovir in the body, but is much better absorbed orally than the latter. The therapeutic effectiveness is frequently compromised by the emergence of drug-resistant virus isolates. A variety of amino acid changes in the UL97 protein kinase and the viral DNA polymerase have been reported to cause drug resistance. Foscarnet or cidofovir are only given to people with CMV resistant to ganciclovir, because foscarnet has notable nephrotoxicity, resulting in increased or decreased Ca2+ or PO43−, and decreased Mg2+ levels. [78] [79]
Letermovir has been approved by the European Medicines Agency [80] and the FDA [81] for treatment and prophylaxis of HCMV infection.
A better understanding of how HCMV supports viral latency and reactivation should allow for the development of new therapies that target the latent reservoir. [82]
All three currently licensed anti-HCMV drugs target the viral DNA polymerase, pUL54. Ganciclovir (GCV) acts as nucleoside analogue. Its antiviral activity requires phosphorylation by the HCMV protein kinase, pUL97. [83] The second drug, Cidofovir (CDV), is a nucleotide analogue, which is already phosphorylated and thus active. Finally, Foscarnet (FOS) has a different mode of action. It directly inhibits polymerase function by blocking the pyrophosphate binding site of pUL54 (note: investigational drug letermovir acts through a mechanism that involves viral terminase). [84] Two HCMV proteins are implicated in antiviral resistance against these three drugs: pUL97 and pUL54. Specific mutations in pUL97 can cause reduced phosphorylation activity of this viral protein kinase. Thus, fewer monophosphorylated – and thus active – GCV can be synthesized, [85] leading to antiviral resistance against GCV. About 90% of all GCV resistances are caused by such mutations in UL97. [86] Mutations in pUL54 may have different effects leading to antiviral drug resistance: A. They can lead to decreased affinity to antiviral compounds. This resistance mechanism concerns GCV, CDV and FOS and may lead to multidrug resistance. [87] B. Some mutations in pUL54 can increase the polymerase's exonuclease activity. This causes enhanced recognition of incorporated GCV and CDV. As a result, these dNTP analogues are excised more efficiently. Major risk factors for HCMV drug resistance are the residual capacity of the host's immune system to control viral replication and the overall amount and duration of viral replication. [88] HCMV antiviral drug resistance can be detected by phenotypic or by genotypic drug resistance testing. Phenotypic resistance testing involves cultivation of the virus in cell culture and testing its susceptibility using different antiviral drug concentrations in order to determine EC50 values. In contrast, genotypic resistance testing means the detection of resistance associated mutations in UL97 and UL54 by sequencing. Genotypic resistance testing is becoming the method of choice because it is faster, but requires previous phenotypic characterisation of each newly found mutation. This can be performed via a web-based search tool Archived 9 January 2016 at the Wayback Machine that links a person's HCMV sequence to a database containing all published UL97 and UL54 mutations and corresponding antiviral drug susceptibility phenotypes. [89]
In the United States, CMV infection rises with age from about 60% of people infected by 6 years of age [38] leveling off at about 85–90% of the population by ages 75–80. [90]
Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Antiviral drugs are a class of antimicrobials, a larger group which also includes antibiotic, antifungal and antiparasitic drugs, or antiviral drugs based on monoclonal antibodies. Most antivirals are considered relatively harmless to the host, and therefore can be used to treat infections. They should be distinguished from virucides, which are not medication but deactivate or destroy virus particles, either inside or outside the body. Natural virucides are produced by some plants such as eucalyptus and Australian tea trees.
Cytomegalovirus (CMV) is a genus of viruses in the order Herpesvirales, in the family Herpesviridae, in the subfamily Betaherpesvirinae. Humans and other primates serve as natural hosts. The 11 species in this genus include human betaherpesvirus 5, which is the species that infects humans. Diseases associated with HHV-5 include mononucleosis and pneumonia, and congenital CMV in infants can lead to deafness and ambulatory problems.
Infectious mononucleosis, also known as glandular fever, is an infection usually caused by the Epstein–Barr virus (EBV). Most people are infected by the virus as children, when the disease produces few or no symptoms. In young adults, the disease often results in fever, sore throat, enlarged lymph nodes in the neck, and fatigue. Most people recover in two to four weeks; however, feeling tired may last for months. The liver or spleen may also become swollen, and in less than one percent of cases splenic rupture may occur.
The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs as a strategy to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of multiple drugs that act on different viral targets is known as highly active antiretroviral therapy (HAART). HAART decreases the patient's total burden of HIV, maintains function of the immune system, and prevents opportunistic infections that often lead to death. HAART also prevents the transmission of HIV between serodiscordant same-sex and opposite-sex partners so long as the HIV-positive partner maintains an undetectable viral load.
Respiratory syncytial virus (RSV), also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a contagious virus that causes infections of the respiratory tract. It is a negative-sense, single-stranded RNA virus. Its name is derived from the large cells known as syncytia that form when infected cells fuse.
Ganciclovir, sold under the brand name Cytovene among others, is an antiviral medication used to treat cytomegalovirus (CMV) infections.
Valganciclovir, sold under the brand name Valcyte among others, is an antiviral medication used to treat cytomegalovirus (CMV) infection in those with HIV/AIDS or following organ transplant. It is often used long term as it only suppresses rather than cures the infection. Valganciclovir is taken by mouth.
Cytomegalovirus retinitis, also known as CMV retinitis, is an inflammation of the retina of the eye that can lead to blindness. Caused by human cytomegalovirus, it occurs predominantly in people whose immune system has been compromised, including 15-40% of those with AIDS.
Herpesviridae is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ἕρπειν, referring to spreading cutaneous lesions, usually involving blisters, seen in flares of herpes simplex 1, herpes simplex 2 and herpes zoster (shingles). In 1971, the International Committee on the Taxonomy of Viruses (ICTV) established Herpesvirus as a genus with 23 viruses among four groups. As of 2020, 115 species are recognized, all but one of which are in one of the three subfamilies. Herpesviruses can cause both latent and lytic infections.
Foscarnet (phosphonomethanoic acid), known by its brand name Foscavir, is an antiviral medication which is primarily used to treat viral infections involving the Herpesviridae family. It is classified as a pyrophosphate analog DNA polymerase inhibitor. Foscarnet is the conjugate base of a chemical compound with the formula HO2CPO3H2 (Trisodium phosphonoformate).
Betaherpesvirinae is a subfamily of viruses in the order Herpesvirales and in the family Herpesviridae. Mammals serve as natural hosts. There are 26 species in this subfamily, divided among 5 genera. Diseases associated with this subfamily include: human cytomegalovirus (HHV-5): congenital CMV infection; HHV-6: 'sixth disease' ; HHV-7: symptoms analogous to the 'sixth disease'.
A Cytomegalovirus vaccine is a vaccine to prevent cytomegalovirus (CMV) infection or curb virus re-activation in persons already infected. Challenges in developing a vaccine include adeptness of CMV in evading the immune system and limited animal models. As of 2018 no such vaccine exists, although a number of vaccine candidates are under investigation. They include recombinant protein, live attenuated, DNA and other vaccines.
As of 2024, a vaccine against Epstein–Barr virus was not yet available. The virus establishes latent infection and causes infectious mononucleosis. There is also increasingly more evidence that EBV may be a trigger of multiple sclerosis. It is a dual-tropic virus, meaning that it infects two different host cell types — in this case, both B cells and epithelial cells. One challenge is that the Epstein–Barr virus expresses very different proteins during its lytic and its latent phases. Antiviral agents act by inhibiting viral DNA replication, but as of 2016, there was little evidence that they are effective against Epstein–Barr virus. They are also expensive, risk causing resistance to antiviral agents, and can cause unpleasant side effects.
There are several forms of Epstein–Barr virus (EBV) infection. These include asymptomatic infections, the primary infection, infectious mononucleosis, and the progression of asymptomatic or primary infections to: 1) any one of various Epstein–Barr virus-associated lymphoproliferative diseases such as chronic active EBV infection, EBV+ hemophagocytic lymphohistiocytosis, Burkitt's lymphoma, and Epstein–Barr virus positive diffuse large B-cell lymphoma, not otherwise specified); 2) non-lymphoid cancers such as Epstein–Barr virus associated gastric cancer, soft tissue sarcomas, leiomyosarcoma, and nasopharyngeal cancers; and 3) Epstein–Barr virus-associated non-lymphoproliferative diseases such as some cases of the immune disorders of multiple sclerosis and systemic lupus erythematosis and the childhood disorders of Alice in Wonderland Syndrome and acute cerebellar ataxia.
Maribavir, sold under the brand name Livtencity, is an antiviral medication that is used to treat post-transplant cytomegalovirus (CMV). Maribavir is a cytomegalovirus pUL97 kinase inhibitor that works by preventing the activity of human cytomegalovirus enzyme pUL97, thus blocking virus replication.
Human betaherpesvirus 7 (HHV-7) is one of nine known members of the Herpesviridae family that infects humans. HHV-7 is a member of Betaherpesvirinae, a subfamily of the Herpesviridae that also includes HHV-6 and Cytomegalovirus. HHV-7 often acts together with HHV-6, and the viruses together are sometimes referred to by their genus, Roseolovirus. HHV-7 was first isolated in 1990 from CD4+ T cells taken from peripheral blood lymphocytes.
A neutralizing antibody (NAb) is an antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically. Neutralization renders the particle no longer infectious or pathogenic. Neutralizing antibodies are part of the humoral response of the adaptive immune system against viruses, bacteria and microbial toxin. By binding specifically to surface structures (antigen) on an infectious particle, neutralizing antibodies prevent the particle from interacting with its host cells it might infect and destroy.
Congenital cytomegalovirus (cCMV) is cytomegalovirus (CMV) infection in a newborn baby. Most have no symptoms. Some affected babies are small. Other signs and symptoms include a rash, jaundice, hepatomegaly, retinitis, and seizures. It may lead to loss of hearing or vision, developmental disability, or a small head.
Cytomegalovirus colitis is an inflammation of the colon.
Letermovir is an antiviral drug for the treatment of cytomegalovirus (CMV) infections. It has been tested in CMV infected patients with allogeneic stem cell transplants and may also be useful for other patients with a compromised immune system such as those with organ transplants or HIV infections. The drug was initially developed by the anti-infective division at Bayer, which became AiCuris Anti-infective Cures AG through a spin-out and progressed the development to end of Phase 2 before the project was sold to Merck & Co for Phase 3 development and approval.
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