MicroBio Notes 21.5
What are the signs and symptoms of influenza?
After a short incubation period averaging 2 days, influenza typically begins with headache, fever, sore throat, and muscle pain, peaking in 6 to 12 hours. A dry cough develops and worsens over a few days. These acute symptoms usually go away within a week, leaving the patient with a lingering cough, fatigue, and generalized weakness for additional days or weeks. Infection by influenza viruses is occasionally associated with Reye's syndrome, a complication linked to certain other viral infections as well.
What are the sings and symptoms of Hantavirus Pulmonary syndrome?
After an incubation period ranging from 3 days to 6 weeks, hantavirus pulmonary syndrome begins with fever, muscle aches (especially in the lower back), nausea, vomiting, and diarrhea. Unproductive cough and increasingly severe shortness of breath appear within a few days, often followed by shock and death.
How else can influenza avoid human immunity?
Another situation arises when a strain that does not typically infect humans gains the ability to do so
What is the causative agent of the Hantavirus pulmonary syndrome?
Hantavirus pulmonary syndrome is caused by a hantavirus called the Sin Nombre virus (SNV)—sin nombre means "no name" in Spanish. Hantaviruses are enveloped viruses of the bunyavirus family. Their genome consists of three segments of single-stranded RNA. In nature, these viruses primarily infect rodents, causing lifetime infections, without any apparent harm to the animals. Each type of hantavirus generally infects a particular rodent species.
What is the causative agent of influenza?
Influenza A virus is an enveloped single-stranded RNA virus belonging to the orthomyxovirus family. The genome is segmented into eight pieces, each of which contains one or two genes. Embedded in the envelope are two kinds of glycoprotein spikes—hemagglutinin antigen (HA) and neuraminidase antigen (NA)—which have a role in viral pathogenesis. The HA spikes allow the virus to recognize and attach to specific receptors on ciliated host epithelial cells, initiating infection. HA spikes cause red blood cells to stick together (hemagglutination), a useful characteristic for virus identification. NA is an enzyme that plays a critical role in the release of newly formed virions from host cells. As new virions are made, they bud out of the host cell but remain bound to surface receptors in the host membrane. NA destroys these receptors, allowing the virions to leave the infected host cell, and aiding the spread of the virus to uninfected host cells.
How is influenza treated?
Like all viral infections, antibiotic treatment is not effective for influenza. Medications such as amantadine and rimantadine have been used for short-term prevention of influenza A disease when vaccination is not an option or while waiting for the protection of vaccination to take effect. However, they are not currently recommended because many circulating viruses are resistant to them. Zanamivir and oseltamivir are neuraminidase inhibitors, active against both A and B viruses. These medicines are generally used together with vaccination to protect exposed people until the vaccine successfully induces immunity.
Describe the pathogenesis of influenza
People acquire influenza virus by inhaling aerosolized respiratory secretions from someone who has the disease or from fomites. The virions attach by their HA spikes to specific receptors on ciliated respiratory epithelial cells and enter the cell by endocytosis. New viral parts are quickly synthesized, and regions of the host cell membrane become embedded with virally encoded HA and NA glycoproteins. Within 6 hours, mature virions bud from the host cell, acquiring host cell-derived membrane containing these HA and NA spikes as they do so. The virus spreads rapidly to nearby cells, including mucus-secreting cells and cells of the alveoli. The common flu signs and symptoms are caused by tissue damage as well as pro-inflammatory cytokines produced by virus-infected cells. Infected epithelial cells die and slough off, thus destroying the mucociliary escalator. The damage to this important first line of defense makes the person susceptible to secondary respiratory infections. The immune response quickly controls the influenza virus infection in most cases, although complete recovery of the respiratory epithelium may take 2 months or more.
How can RSV be prevented?
Preventing healthcare-associated RSV illness requires strict isolation techniques. People with underlying illnesses and infants at high risk can be protected from the disease by giving them passive immunity via monthly injections of immune globulin or a monoclonal antibody called palivizumab. No vaccines are available.
Is there a way to prevent the hantavirus pulmonary syndrome?
Prevention of the syndrome is based on minimizing exposure to rodents and dusts contaminated by their urine, saliva, and feces. Rodent populations should be controlled by keeping foods in containers and making buildings as mouse-proof as possible. When cleaning an area where rodents are found, maximal ventilation should be ensured, and the area should be mopped with a disinfectant solution rather than being swept with brooms and vacuum cleaners that can stir up dust. Lethal traps and poisons may be necessary to decrease the rodent population in the area.
What is the causative agent of RSV?
RSV is a single-stranded, enveloped RNA virus of the paramyxovirus group. It causes cells in cell cultures to fuse together; the clumps of fused cells are known as syncytia, thus the name of the virus
Describe the epidemiology of RSV
RSV outbreaks are common from late fall to late spring, peaking in mid-winter. Recovery from infection produces only weak and short-lived immunity, so that infections can recur throughout life. Healthy children and adults usually have mild illness and readily spread the virus to others.
What are the signs and symptoms of Respiratory Syncytial Virus infections? (RSV)
Signs and symptoms of RSV infection begin after an incubation period of 1 to 4 days with runny nose followed by cough, wheezing, and difficulty breathing. Fever may or may not be present. Patients often develop a dusky color, indicating that they are not getting enough O2. Healthy older children and adults with RSV generally show symptoms of a bad cold. RSV is one of the causes of croup, which manifests as a loud high-pitched cough and noisy inhalation due to airway obstruction.
Describe the pathogenesis of RSV
The virus enters the body by inhalation and infects the respiratory tract epithelium, causing cells to die and slough off. Bronchiolitis is a common feature of the disease; the inflamed bronchioles become partially plugged by sloughed cells, mucus, and clotted plasma that has oozed from the walls of the bronchi. The initial obstruction causes wheezing when air rushes through the narrowed passageways, sometimes causing the condition to be confused with asthma. The obstruction often acts like a one-way valve, allowing air to enter the lungs, but not leave them. In many cases the inflammatory process extends into the alveoli, causing pneumonia. There is a high risk of secondary infection because of the damaged mucociliary escalator.
Describe the pathogenesis of the hantavirus pulmonary syndrome
The virus enters the body by inhalation of airborne dust contaminated with the urine, feces, or saliva of infected rodents. The virus then enters the circulation and is carried throughout the body, infecting the cells that line tissue capillaries. Massive amounts of the viral antigen appear in lung capillaries, but the antigen is also found in capillaries of the heart and other organs. The inflammatory response to the viral antigen causes the vessels to leak large amounts of plasma into the lungs, suffocating the patient and causing the blood pressure to fall. Shock and death occur in about 30% of the cases. Luckily, despite the large amount of viral antigen in the lung capillaries, few mature infectious virions enter the air passages of the lung, so person-to-person transmission occurs only rarely, if ever.
What are the different subtypes of influenza?
There are different subtypes of influenza A viruses, characterized by antigenically distinct HA and NA spikes. The subtypes are given numbers according to these variations—H1, H2, N1, N2 and so on. For example, the "avian flu" epidemic of 1997 was caused by influenza virus H5N1, whereas the "swine flu" epidemic of 2009 was caused by influenza virus H1N1. There are 16 HA and 9 NA subtypes, but only H1, 2 and 3, and N1 and 2 spread among humans.
Is there a treatment for RSV?
There are no effective antiviral medications for treating RSV.
Is there a treatment of the hantavirus pulmonary syndrome
There is no proven antiviral treatment for hantavirus pulmonary syndrome, a highly fatal disease.
Antigenic shift
This is an uncommon but more dramatic change that occurs as a result of viral genome reassortment and is the cause of pandemic influenza. Recall that the influenza virus genome is segmented, meaning that viral proteins are encoded on eight different RNA segments rather than being encoded on one long molecule. Because of this characteristic, when two different influenza viruses infect a cell at the same time, the progeny produced can have RNA segments from either of the viruses. From an infectious disease standpoint, this is particularly problematic when a genome segment from a virus that normally infects only a non-human host is acquired by a strain that infects humans.
Antigenic drift
This is caused by minor mutations in the genes that code for the HA and NA antigens and is responsible for the yearly occurrence of influenza outbreaks, called seasonal influenza. The mutations happen during normal viral replication and often cause a change in only a single amino acid in the HA or NA spikes. They occur frequently, however, and are enough to make immunity developed to virus strains of previous years less effective. This ensures a continual supply of susceptible hosts within which the virus can multiply. Strains that arise because of antigenic drift are given names indicating the year and location they were isolated.
How is influenza prevented?
Vaccination is used to prevent influenza, but new vaccines must be developed annually because the viruses change so quickly. These vaccines are trivalent or quadrivalent, meaning they are against three or four strains—two influenza A viruses (usually an H3N2 strain and an H1N1 strain) and one or two influenza B viruses. Once the vaccine composition is chosen, it takes 6 to 9 months for manufacturers to generate adequate amounts. A variety of different vaccine types are now available, including inactivated influenza vaccine (IIV), recombinant influenza vaccine (RIV), and live attenuated influenza vaccine (LAIV). The choice of which vaccine type to use depends on patient characteristics. For example, a new high-dose vaccine is available for people over 65, and the RIV is not made in eggs, so it can be administered to people who are allergic to eggs.
Describe the epidemiology of the hantavirus pulmonary syndrome
Zoonosis likely to involve humans in proximity to increasing mouse populations; generally no person-to-person spread.
