Poxviruses Overview PDF

Poxviruses, Orthomyxoviruses and Rhabdovirus Dr. kaveh Sadeghi PhD of Medical Virology Department of Microbiology, School of Medicine, Tehran University of Medical Sciences ...

Poxviruses, Orthomyxoviruses and Rhabdovirus Dr. kaveh Sadeghi PhD of Medical Virology Department of Microbiology, School of Medicine, Tehran University of Medical Sciences  Poxviruses Structure and Composition The virion contains a multiplicity of enzymes, including: a transcriptional system that can synthesize, polyadenylate, cap, and methylate viral mRNA.  Poxviruses cowpox, monkeypox, vaccinia, and variola (smallpox) viruses are infectious for humans. Poxviruses are unique among DNA viruses in that the entire multiplication cycle takes place in the cytoplasm of infected cells. Among the several enzymes inside the poxvirus particle, there is a viral RNA polymerase that transcribes about half the viral genome into early mRNA. These mRNAs are transcribed within the viral core and are then released into the cytoplasm Because the necessary enzymes are contained within the viral core, early transcription is not affected by inhibitors of protein synthesis The second-stage uncoating step liberates viral DNA from the cores; it requires both RNA and protein synthesis. The synthesis of host cell macromolecules is inhibited at this stage  Poxviruses Poxviruses inactivated by heat can be reactivated either by viable poxviruses or by poxviruses inactivated by nitrogen mustards (which inactivate the DNA). This process is called nongenetic reactivation. A polypeptide encoded by one of the early genes of vaccinia virus is closely related to epidermal growth factor and to transforming growth factor-α. could account for the proliferative diseases associated : molluscum contagiosum viruses.  Poxviruses Control and Eradication of Smallpox : Edward Jenner introduced vaccination with live cowpox virus in 1798 Smallpox was officially declared eliminated in 1980 There were several reasons for this outstanding success: There is a single serotype of virus; most infections are clinically apparent; the vaccine was easily prepared, stable, and safe; the vaccine could be given simply by personnel in the field; and mass vaccination of the world population was not necessary. Cases of smallpox were traced, and contacts of the patient and those in the immediate area were vaccinated. There was no known nonhuman reservoir Chronic asymptomatic carriage of the virus did not occur.  Poxviruses Comparison of Vaccinia and Variola Viruses : Vaccinia virus, the agent used for smallpox vaccination Variola has a narrow host range (only humans and monkeys), but vaccinia has a broad host range that includes rabbits and mice. Both vaccinia and variola viruses grow on the chorioallantoic membrane of the 10- to 12-day-old chick embryo Of 187 putative proteins, 150 were markedly similar in sequence between the two viruses Pathogenesis and Pathology of Smallpox : (1) primary multiplication in the lymphoid tissue draining the site of entry; (2) transient viremia and infection of reticuloendothelial cells throughout the body; (3) a secondary phase of multiplication in those cells, leading to (4) a secondary, more intense viremia; and (5) the clinical disease.  Poxviruses In the presumptive phase, the disease was barely infective. By the sixth to ninth day, lesions in the mouth tended to ulcerate and discharge virus. Thus, early in the disease, infectious virus originated in lesions in the mouth and upper respiratory tract. Later, pustules broke down and discharged virus into the environment of the smallpox patient. All of the layers of the skin were involved, with subsequent dermal necrosis. Thus, scarring occurred after variola infection. Clinical Findings: One to 5 days of fever and malaise preceded the appearance of the exanthems, which began as macules, then papules, then vesicles, and finally pustules. in each affected area, the lesions were generally found in the same stage of development (in contrast to chickenpox).  Poxviruses Lesions were most abundant on the face and less so on the trunk. In severe cases, the rash was hemorrhagic The case fatality rate varied from 5% to 40%.  Poxviruses Immunity : All viruses within the Orthopoxvirus genus are so closely related antigenically : Infection with one induces an immune response that reacts with all other members of the group. Antibodies alone are not sufficient for recovery from primary poxvirus infection. Cell-mediated immunity is probably more important than circulating antibody. Isolation and Identification of Virus: Skin lesions are the specimen of choice for viral detection and isolation Cell cultures can be used for virus isolation, though culture of variola virus is only attempted in Biosafety Level 4 facilities  Poxviruses Treatment: Vaccinia immune globulin has not shown a survival benefit for established disease. Methisazone : as prophylaxis but is not useful in treatment Cidofovir : It has been used to treat molluscum contagiosum and orf virus infections. Epidemiology : The virus was stable in the extracellular environment but was most commonly transmitted by respiratory spread. The dried virus in crusts from skin lesions could survive on clothes.  Poxviruses MONKEYPOX INFECTIONS : The disease is a rare zoonosis The clinical features of human monkeypox are similar to those of smallpox, but usually less severe Complications are common and often serious. These are generally pulmonary distress and secondary bacterial infections. In unvaccinated patients, the fatality rate can reach about 10%. Vaccination with vaccinia either protects against monkeypox or lessens the severity of disease. not to be easily transmitted from person to person. COWPOX INFECTIONS : the lesions being confined to the teats and udders. The disease is more severe in unvaccinated persons than in those vaccinated with vaccinia virus. It is also closely related immunologically to variola virus.  MONKEYPOX (Mpox) People with mpox often get a rash and may have other symptoms like fever, chills, and swollen lymph nodes. Symptoms usually start within 21 days of exposure.  Poxviruses Cowpox virus can be distinguished from vaccinia virus by the deep red hemorrhagic. ORF VIRUS INFECTIONS : The orf virus is a species of Parapoxvirus. It causes a disease in sheep and goats that is prevalent worldwide The disease is also called contagious pustular dermatitis or sore mouth infection. Infection of humans occurs usually as a single lesion on a finger, hand, or forearm Lesions are large nodules, rather painful, with surrounding inflamed skin.  Poxviruses MOLLUSCUM CONTAGIOSUM: Molluscum contagiosum is a benign epidermal tumor that occurs only in humans The lesions of this disease are small, pink, wart-like tumors on the face, arms, back, and buttocks The incidence of molluscum contagiosum as a sexually transmitted disease in young adults is increasing. typical lesion is an umbilicated papule, lesions in moist genital areas may become inflamed or ulcerated and may be confused with those produced by herpes simplex virus (HSV). The virus is a poor immunogen; about  Orthomyxoviruses Structure and Composition The single-stranded, negative-sense RNA genomes of influenza A and B viruses occur as eight separate segments; influenza C viruses contain seven segments of RNA, lacking a neuraminidase gene  Orthomyxoviruses Proteins :  Orthomyxoviruses genetic reassortment : Because of the segmented nature of the genome, when a cell is coinfected by two different viruses of a given type, mixtures of parental gene segments may be assembled into progeny virions. may result in sudden changes in viral surface antigens a property that explains the epidemiologic features of influenza and poses significant problems for vaccine development  Orthomyxoviruses Classification and Nomenclature: Genus: Influenzavirus A Influenzavirus B Influenzavirus C Antigenic differences exhibited by two of the internal structural proteins, the nucleocapsid (NP) and matrix (M) proteins, are used to divide influenza viruses into types A, B and C. These proteins possess no cross-reactivity among the three types Antigenic variations in the surface glycoproteins, HA and NA, are used to subtype type A viruses : H1N1, H3N2, … (human) H5N1, H9N2, …( bird )  Orthomyxoviruses Structure and Function of Hemagglutinin (HA) : The HA protein of influenza virus binds virus particles to susceptible cells and is the major antigen against which neutralizing (protective) antibodies are directed Variability in HA is primarily responsible for the continual evolution of new strains and subsequent influenza epidemics Five antigenic sites on the HA molecule exhibit extensive mutations Influenza viruses normally remain confined to the respiratory tract because the protease enzymes that cleave HA are expressed only at those sites. The HA protein is cleaved into two subunits, HA1 and HA2 HA1 = bind to cell surface HA2 = fusion virus with endosome membrane  Orthomyxoviruses Structure and Function of Neuraminidase: The NA functions at the end of the viral replication cycle. It is a sialidase enzyme that removes sialic acid from lycoconjugates. It facilitates release of virus particles from infected cell surfaces during the budding process and helps prevent self-aggregation of virions by removing sialic acid residues from viral glycoproteins. NA helps the virus negotiate through the mucin layer in the respiratory tract to reach the target epithelial cells. Antigenic Drift and Antigenic Shift : Antigenic drift : is caused by the accumulation of point mutations in the gene, resulting in amino acid changes in the protein. Sequence changes can alter antigenic sites on the molecule such that a virion can escape recognition by the host’s immune system. Antigenic shift : reflects drastic changes in the sequence of a viral surface protein, caused by genetic reassortment between human, swine, and avian influenza viruses. Influenza B and C viruses do not exhibit antigenic shift because few related viruses exist in animals.  Orthomyxoviruses Pathogenesis and Pathology: Influenza virus spreads from person to person by airborne droplets. The incubation period from exposure to virus and the onset of illness varies from 1 day to 4 days. Viral shedding starts the day preceding onset of symptoms, peaks within 24 hours, remains elevated for 1–2 days, and then declines over the next 5 days. Infectious virus not recovered from blood. Influenza infections cause cellular destruction of the superficial mucosa of the respiratory tract but do not affect the basal layer of epithelium.  Orthomyxoviruses Edema and mononuclear infiltrations in response to cytokine release and cell death caused by viral replication The fever and systemic symptoms associated with influenza reflect the action of cytokines. Clinical Findings : Respiratory symptoms typically last another 3–4 days. Pneumonia : Pneumonia complicating influenza infections can be viral, secondary bacterial, or a combination of the two. Reye Syndrome : 1- Reye syndrome is an acute encephalopathy of children and adolescents, usually between 2 and 16 years of age 2- There is an epidemiologic relationship between salicylate use and subsequent development of Reye syndrome.  key differences 1- COVID-19 symptoms generally appear 2 to 14 days after exposure, while flu symptoms typically emerge 1 to 4 days after exposure. 2- COVID-19 can also lead to additional symptoms like loss of taste or smell. 3- Bacterial respiratory infection: shortness of breath and can involve a higher risk of persistent coughing. 4- RSV typically causes respiratory symptoms more pronounced in young children, such as wheezing and difficulty breathing.  Orthomyxoviruses Immunity: antibodies against HA and NA are important in immunity to influenza. The cytotoxic T lymphocyte response is cross-reactive (able to lyse cells infected with any subtype of virus) and appears to be directed against both internal proteins (NP, M) and the surface glycoproteins. Laboratory Diagnosis: 1- RT-PCR is rapid sensitive, and specific. 2- Isolation and Identification of Virus : embryonated eggs and primary monkey kidney cells 3- Serology: Routine sero diagnostic tests in use are based on HI (Hemagglutination Inhibition). Antigenic Change : Periodic outbreaks appear because of antigenic changes in one or both surface glycoproteins of the virus  Orthomyxoviruses All three types of influenza virus exhibit antigenic drift. However, only influenza A undergoes antigenic shift Spanish flu epidemic (H1N1) : 1918 Prevention and Treatment by Drugs Amantadine and rimantadine block M2 protein ( channel ) NA inhibiros zanamivir and oseltamivir oseltamivir has been associated with the H275Y mutation in NA gene. Inactivated Viral Vaccines : 1-cocktail containing two type A (H1N1, H3N2) viruses and one type B virus. 2-Selected seed strains are grown in embryonated eggs.3- inactivated with formalin or β- propiolactone.  Orthomyxoviruses Live-Virus Vaccines: A cold-adapted donor virus, able to grow at 25°C but not at 37°C—the temperature of the lower respiratory tract—should replicate in the nasopharynx, which has a cooler temperature (33°C).  rhabdovirus Properties of Rhabdoviruses:  Rabies Rabies is spread to humans and pets primarily through bites or scratches from an infected animal  rhabdovirus Virus Replication : nicotinic acetylcholine receptor as a cellular receptor for rabies virus. Rabies virus has a wide host range. All warm-blooded animals, including humans, can be infected. The virus is widely distributed in infected animals, especially in the nervous system, saliva, urine, lymph, milk, and blood. Pathogenesis and Pathology: Rabies virus multiplies in muscle or connective tissue at the site of inoculation and then enters peripheral nerves at neuromuscular junctions and spreads up the nerves to the central nervous system. It multiplies in the central nervous system and progressive encephalitis develops. The virus then spreads through peripheral nerves to the salivary glands and other tissues  rhabdovirus Rabies virus produces a specific eosinophilic cytoplasmic inclusion, the Negri body, in infected nerve cells Clinical Findings Rabies is primarily a disease of lower animals and is spread to humans by bites of rabid animals or by contact with saliva from rabid animals. The incubation period in humans is typically 1–3 months. he clinical spectrum can be divided into three phases: a short prodromal phase, an acute neurologic phase, and coma. A large fraction of patients will exhibit hydrophobia (fear of water) or aerophobia (fear when feeling a breeze). The major cause of death is cardiorespiratory arrest  rhabdovirus Laboratory Diagnosis Rabies can be diagnosed from euthanized animals by direct fluorescent antibody testing of brain tissue. A biopsy specimen is usually taken from the skin of the neck at the hairline. Impression preparations of brain or cornea tissue may be used (immunofluorescence or immunoperoxidase staining by antibody). Reverse transcription-polymerase chain reaction testing (RT-PCR) : from fixed or unfixed brain tissue or saliva Serology Immunity and Prevention: Only one antigenic type of rabies virus is known  rhabdovirus Vaccines : All vaccines for human use contain only inactivated rabies virus Types of Rabies Antibody : 1-Rabies immune globulin, human 2- Anti-rabies serum, equine Postexposure Prophylaxis : ? There is no successful treatment for clinical rabies