CMV Flashcards
CMV is part of herpes virus family, known as HHV5
What is structure of CMV virus?
CMV is spherical in shape with icosahedral symmetry.
double-stranded DNA genome with 230 kbp
Nucleocapsid surround nuclear material
Nucleocapsid surrounded by proteinaceous layer, the tegument. Contains enzymes such as VP16, which is responsible for subverting cellular proteins and enzymes to involve in viral nucleic acid replication. Contains Virion Host Shutoff VHS protein, which shuts down host cell protein synthesis.
This is then surrounded by an envelope which is lipoprotein in nature. The lipid part is derived from the nuclear membrane of the infected host cell.
gH glycoprotein binds to host receptors.
gB glyvcoprotein assists in fusion, and mediates virus entry.
What is known about structure of CMV genome?
The CMV genome consists of approximately 230kb of linear double-stranded DNA.
The genome is split into a unique long (UL) and a unique short (US) region, both flanked by inverted sequences.
It contains approximately 150 open reading frames (ORFs) that encode proteins.
Out of these, it has been found that 41 are essential and 117 are nonessential for CMV replication.
How is CMV transmitted?
CMV infections occur worldwide and the prevalence of infection varies considerably - up to 70% of all adults infected
- transcplanetnal
- breast milk
- saliva - kissing
- urine
- sexually - found in secretions
- blood transfusion/ organ donation
Congenital CMV infection is the most common viral infection of human fetuses with 1% in the USA and 2-3% in developing countries.
How does CMV replicate?
Attachment to host cells is mediated by the fusion of the viral glycoproteins to host receptors which further mediates endocytosis of the virus into the host cell.
After entry and uncoating, the capsid is transported to the nuclear pore where the viral DNA is released into the nucleus.
Tegument proteins regulate host cell responses and initiate the temporal cascade of the expression of viral I immediate-early (IE) genes, followed by delayed early (DE) genes, which initiate viral genome replication, and late (L) genes.
Late gene expression initiates capsid assembly in the nucleus, followed by nuclear egress to the cytosol.
Capsids associate with tegument proteins in the cytosol and are trafficked to the viral assembly complex (AC) that contains components of the endoplasmic reticulum (ER), Golgi apparatus and endosomal machinery.
The capsids further acquire tegument and viral envelope by budding into intracellular vesicles at the assembly complex.
Assembly of the virus in nuclear viral factories and budding through the inner lamella of the nuclear membrane by the insertion of herpes glycoproteins, throughout the Golgi and final release by exocytosis at the plasma membrane.
What is pathogenesis of CMV infection?
HCMV infects and replicates in a wide variety of cells, including epithelial cells of the gland and mucosal tissue, smooth muscle cells, fibroblasts, macrophages, dendritic cells, hepatocytes, and vascular endothelial cells.
This broad cell tropism facilitates systemic spread in the human body and inter-host spread.
Primary replication typically starts with replication in the mucosal epithelium as a result of direct contact with infectious secretions from an infected individual.
A systemic phase of infection disseminates virus in the host via leukocyte associated viremia that may last for several months.
In addition, HCMV undergoes latency in myeloid cells of the bone marrow, presumably leading to a life-long infection with sporadic reactivation.
HCMV infection is generally asymptomatic in healthy individuals. However, in immunocompromised individuals, such as organ transplant recipients or human immunodeficiency virus carriers, HCMV poses a life-threatening risk.
HCMV is also recognized as the leading infectious cause of congenital neurological disease by transmission through the placenta from the mother to the child.
CMV specific IgM antibodies are produced during the primary infection and persist for 3 or 4 months, but are not produced in recurrent infections in immunocompetent individuals.
CMV IgG antibodies are produced at the time of primary infection and persist lifelong.
With intrauterine infections, both IgM and IgG are produced by the fetus but the fetal IgG response can only be detected as the passively acquired IgG from the mother is catabolized.
On the other hand, Cell-mediated immunity (CMI) is thought to play a key role in the suppression of CMI infection.
Because CMV can affect many organ systems, it can present in a multitude of ways.
What are most common presentations?
immunocompetent -
Acute CMV infection may mimic infectious mononucleosis caused by Epstein-Barr virus or liver infection by hepatitis A, B, or C.
Mono-like symptoms may include fever, malaise, enlarged lymph nodes, sore throat, muscle aches, loss of appetite, enlarged liver or spleen, and fatigue.
Hepatitis-like symptoms and signs may include appetite loss, yellow eyes, nausea, and diarrhea.
immunocompromised -
- retinitis
- pnemonia
- oesophagitis
- enteritis
- hepatitis
- encephalitis
Congenital -
- deafness
- jaundice
- premature birth
- LBW
- pneumonia
- hepatosplenomegaly
- microcepahly
- mental retardation
- haemolytic anaemia
- cerebral palsy
how to diagnose CMV infection?
Commonly send urine/ saliva/ blood
Serology/ PCR are most commonly used methods
Viral load >2000 copies/ ml suggests significant viraemia, which will precede clinical disease.
Cytopathology - intracellular inclusions surrounded by a clear halo may be demonstrated with various stains (Giemsa, Wright, hematoxylin-eosin, Papanicolaou).
Cytomegalic inclusions can be recognized from biopsy material by the typical “owl’s eyes appearance “.
Tissue immunofluorescence
Infected lung and liver cells may be stained by specific anti-CMV antibodies.
Immunohistochemistry - performed primarily on tissue or body fluid samples. Slides are made from frozen sections of biopsy tissue samples (liver, lung) or by centrifuging cells onto a slide. Then monoclonal or polyclonal antibodies against early CMV antigens are applied and visualized by fluorescently labeled antibodies or enzyme-labeled secondary antibodies which are visualized by the change of color of the substrate. The stained slides are then examined by fluorescent or light microscopy.
Antigen detection - detection of the CMV pp65 antigen in leukocytes. The pp65 assay is used to detect messenger matrix proteins on the CMV virus, with either immunofluorescence assay or messenger RNA amplification
Serology - useful for determining whether a patient has had CMV infection in the past, determined by the presence or absence of CMV IgG/ IgM
Molecular methods
Polymerase chain reaction (PCR) is a widely available rapid and sensitive method of CMV detection based on the amplification of nucleic acids. Can use Guthrie card if think antenatally acquired
What is treatment of CMV infection?
Treat if evidence of end organ disease, or if two results of CMV VL >2000 whilst monitoring patient
Immunocompetent and symptomatic
Immunocompromised and symptomatic
Prophylaxis following transplant
- Immunocompetent and symptomatic (fever, malaise, lymphadenopathy) - no treatment
- Immunocompromised and symptomatic - ganciclovir IV until resolution of symptoms, minimum 14 days.
Ganciclovir 5mg/kg BD
Oral valganciclovir can be used 900mg BD - Foscarnet/ cidofovir are second line drugs
- If HIV start ART
- After treatment, give prophylaxis for 1-3 months, to prevent risk of re-infection
Oral valganciclovir 900mg OD for 100-200 days. Start within 10 days of transplantation
If CMV DNA levels increase, switch to treatment dose
How to prevent/ control spread of CMV?
Glove/ apron for pregnant nurses exposed on neonatal unit - this reduces risk of spread to normal population risk
Isolation of newborns with disease from other newborns
Screening of transplant donors and recipients for CMV antibody. Even if antibodies to CMV, if receiving organ, there is risk of re-infection with different strain of virus.
If donor/ recipient CMV negative, use seronegative/ leukodepleted blood products
Both live and recombinant vaccines are under development.
CMV in transplant patients.
What to do if CMV-seronegative recipient receiving from seropositive donor?
CMV-seronegative recipients who receive a solid organ transplant from a donor who is seropositive, should be offered prophylaxis against primary infection, using oral valganciclovir, oral valaciclovir or intravenous ganciclovir.
The same should apply where either the donor or recipient is seropositive if the patient is treated with T-cell depleting therapies.
Continue prophylaxis for 3-6 months
CMV in transplant patients
What to do if donor and recipient are both seropositive, and patient is not treated with T-cell therapy
Renal
Liver
Lung
Heart
For renal/ liver/ cardiac transplant recipients: no prophylaxis is recommended.
For lung transplant recipients: the recommended prophylactic strategy is oral valganciclovir or oral valaciclovir.
Which neonates should be offered treatment?
Treatment must be started within first 4 weeks of life. After this, no evidence of any benefit
Severe CMV -
- CNS involvement
- Acutely unwell with single organ disease, awaiting further diagnosis e.g hepatosplenomegaly, bone marrow suppression, pneumonitis, colitis
Moderate CMV - some symptoms e.g dernaged LFTs/ haematology, bruising, mild hepatomegaly. unclear whether to treat
Mild CMV - asymptomatic, or insignificant symptoms, do not treat.
Higher risk if acquired in first trimester
Higher risk if ante-natally acquired
If CMV not acquired ante-natally, we may suspect it is acquired post-natally.
Who should we treat?
Post natal infection does not normally cause significant problems in term infants but may do in preterm infants.
Treatment should be considered in infants with severe symptoms and discussed with the paediatric infectious disease team prior to commencement for an individualised treatment plan.
What is treatment of congenital CMV?
(only treat ante-natally acquired. Post-natally-acquired usually not have issues)
Acutely unwell infants with severe focal or multisystem disease
Acutely unwell infants with severe focal or multisystem disease
- Ganciclovir 6mg/kg twice daily by intravenous infusion (central line)
- Change to oral valganciclovir 16mg/kg twice daily (unless renal impairment) when the infant is on approximately 50% enteral feeds.
Patients on oral valganciclovir have fewer side effects (neutropenia) than patients on ganciclovir and this switch will obviate the need to maintain central venous access
Total duration treatment 6 months. Switch to oral once improved
Suspected neonatal CMV.
What investigations are required?
- baby - test within first 3 weeks of life
- mother
FBc U+E LFT Coag Buccal/ urine - CMV PCR.
Neuroimaging - cranial USS/ CT - CNS calcification
Ophthalmology
Audiology
Mother booking bloods -
IgM/IgG
IgG avidity
CMV viral load
first trimester maternal infection is associated with higher risk of symptomatic infection and neurological sequelae
