Composition: Live attenuated virus.
Measles: Schwartz or Moraten substrains of Edmonston B strain.
Mumps: Jeryl Lynn strain.
Rubella: RA/27-3 strain.
Vaccination schedule: at 12-15 months and again at 4-6 years or before middle school.
Efficiency: 95% lifelong immunization with a single dose.

Influenza virus vaccines:

• Formalin-inactivated whole virus
• Chemically disrupted virus (subvirion)
• Purified antigens

Influenza properties:

• Eight RNA segments
• Antigenic shift and drift
• Respiratory transmission
• Frequent childhood and adult disease

It has two binding proteins: a hemagglutinin (H) and a neuramidinase (N). These, combined with the location and strain of the virus, are used in nomenclature:

A/Ann Arbor/6/60 (H2N2)
strain, location, serial #, year, type

HA binds to salicylic acid. These receptors are only in the respiratory tract. There are different types of linkage:

• α2-3 linkage on avian cells
• α2-6 linkage on avian cells
• α2-3 & α2-6 linkage on avian cells

Antigenic Variation in Influenza

Antigenic variation in influenza virus can occur by antigen shift and antigenic drift. In antigenic drift, small changes accumulate in the epitopes of HA and NA due to RNA replication errors (mutations). This causes the annual variations in influenza. In antigenic shift, a human virus and an animal virus co-infect the same cell, resulting in reassortment of viral RNA segments. Antigenic shift can cause a pandemic if a new virus emerges that:

• Has mostly human RNA
• Has human or animal hemagglutinin protein with high affinity for human cells
• Humans have not evolved antibodies against.

Influenza virus is ana vain virus. There are 15 types of HA and 9 types of N. By resassortment, a new HA can come into the human populaiton. BY antigenic drift, the HA protein can addapt to bind better to the human sialic acid receptor α2-6. There are three human A strains (H1N1, H2N2, H3N2) in addition to strain B. They can all adapt easily to bind to the human receptor. The human HA protien is cleaved only in the lung, meaning the humans strains are infectious only in the lung.

H5N1, an influenza, binds well onto to &alpha2-3 sialic acid. It contains RNA segments that help produce disease. For example, one RNA segment turns off a component of the immune system. H5 is cleaved by the protease furin, which is present in all cells. Therefore, H5N1 is a pantropic virus able to infect all tissues of avians. It is so pathogenic because, although most human lung cells express α2-6 sialic acid, there are a few expressing α2-3 sialic acid. The H5N1 virus infects these cells and causes a potentially fatal very strong immune response. It can infect poultry, and may adapt to be transmissble from human-to-human.

Influenza has two modes of transmission: person-to-person and by respiratory droplets. Classic flu-like symptoms include:

• Fever
• Malaise
• Myalgia (muscular pain)
• Sore throat
• Nonproductive cough

Influenza virus uses the caps of eukaryotic mRNAs instead of synthesizing its own. This was concluded by a series of experiments:

• Actinomycin D inhibits DNA-dependent RNA transcription. Influenza virus transcription is inhbited by Actinomycin D. As a result, it was proposed than nucleus plays a role in viral replication.
• α-amantin is an inhibitor of DNA-dependent RNAP II. It was shown that it inhibited transcription of influenza virus in a cell but not in vitro. This inhibition by α-amantin led to experiments regarding the role of cellular RNA transcription in viral RNA synthesis. In vitro transcritpion was performed using:
  • Detergent-disrupted virions, which provide viral RNA templants and polymerases.
  • Labeled nucleotides
• The dinucleotide ApG, which is complementary to the first 2 nucleotides at 3′ end of each viral RNA segment (3′-UpCpG…5′) was shown to stimulate transcription. It was also shown that ApG was incorporated directly into the 5′ end of the newly synthesized transcript. It is unusual for a dinucleotide to stimulate transcription.
• Dr. Krug showed that globin mRNA, even more than ApG, greatly stimulates in vitro transcritption. He went on to show that the globin mRNA m⁷GpppG can structure was transferred to the influenza virus mRNA transcript.

Krug’s Cap-Stealing Experiment was as follows:

• Globin mRNA added to in vitro transcription stimulates that reaction compared to no globin mRNA added.
• Decapped globin mRNA does not stimulate in vitro transcription, compared to normal globin mRNA.
• Decapped globin mRNA is used to put a ³²P-labeled cap back on, which transfers radioactivity to viral mRNA synthesized in vitro, as shown by gel migration.

Summary: viral polymerase is unable to cap the viral mRNAs. Because uncapped mRNAs are unstable, the virus steals caps from cellular mRNAs. Thus, replication of influenza virus is inhibited by drugs that block DNA-dependent RNA synthesis since these drugs remove a source of cap structures for the virus to steal.

Influenza viruses enter cells via receptor-mediated endocytosis, a kind of engulfment. Following internalization, the vesicle is with an endosome. Endosomes are acidic, and this low pH activates the M2 ion channel. This allows ions to enter the virion, leading to a conformational change in the HA protein. The virus is internalized into clathrin-coated, membrane-bound vesicles.

Amantidine blocks influenza virus replication. Viral mutants resistant to amantidine map to the trans membrane domain of the M2 protein.

Summary: Upon entry into the cell, the enveloped virus resides in a low pH endosome. The viral M2 protein, part of the envelope, serves as an ion channel to further reduce the pH. This induces a conformational change in the HA protein, causing it to protrude forward and effecting a fusion of the viral envelope with the membrane of the endosome. This releases the nucleocapsid into the cytoplasm.

Rhabdoviruses are rod- or bullet-shaped enveloped viruses with a single strand minus-sense RNA genome. The significant members are rabies virus and a well-characterized laboratory strain Vesicular Stomatitis virus.

Epidemiology Rabies is distributed in most of the world except Australia and Antartica. The epidemiology reflects that of animals in the community. Where canine rabies remains common, most cases of human rabies come from dog bites. In locations where dogs are vaccinated, most cases of rabies come from exposure to rabid wild animals. In 1992 there were 36,000 cases of rabies globally. In the U.S., there have been very few human cases of rabies. However, there were 20,000 cases of racoon rabies in the eastern U.S., in addition to cases from coyotes and bats. Prophylaxis, which is vaccination of domestic animals, has reduced incidence of rabies.

Pathogenesis Following introduction through a break in skin, mucosal surfaces, or respiratory tract, rabies virus replicates in muscle cells and then spreads to neurons of PNS and CNS. It produces severe, oftentimes fatal, CNS disfunction.

Clinical Manifestations The viral inoculum plays an important role in rate of clinical disease. A bite on exposed skin is much more likely to cause infection than a bite through thick clothing. Mutliple bites are more likely to result in infection than a single bite. The incubation period varies from a few days to over 19 years, although most (75%) of pateints become ill within 90 days of exposure. Initial symptoms are associated with other systemic viral infections, such as fever, headache, malaise, and disorders of upper repiratory and gastrointestinal tract. Neurologic complaints during this period include subtle changes in personality and cognition as well as pain at the exposure site.

Human rabies infections are divided into 2 forms: furious and paralytic.

Diagnosis Diagnosis is simple. If somebody has suffered a bite from a rabid animal and exhibits hydrophobia, then they have rabies.

Treatment The wound should be washed thoroughly with 20% soap solution to strip the viral envelope. A healthy dog or cat is observed for 10 days. If behavior is normal, the patient needs only wound care. If the animal exhibits symptoms of rabies, it is tested for rabies virus infection. Rabies immunoglobulin is injected equally into both the gluteus maximus and the would area itself.

It has only one RNA segment, meaning all genetic information is in one long RNA strand. It is an enveloped virus, which makes it very unstable. These envelopes are part of the cell membrane of the mamallian cell. The wall is unstable and easily dissolved, unlike polio which has a protein capsid and is very stable in the environemnt. Enveloped viruses tend to be very unstable because the bilayer is easily degraded. The viral attachment protein extends through the envelope, and without the envelope the virus is left with a very stable capsid that is uninfectious. It is unable to infect the mamallian cell because it lacks the viral attachment proteins in the bilayer.

Transmission Parainfluenza is transmitted via sneezing, virus shedding, and contact with eyes and nose. It gets into upper respiratory tracts and the trachea swell, resulting in croup. There is no vaccine for parainfluenza virus. It is mostly a pediatric virus.

Respiratory syncytial virus fuses membranes together to make enormous cells (fused aggregates). These aggregates get into alveoli of the lower respiratory tract, and the patient has trouble breathing out. It is more invasive than parainfluenza virus, as it goes deeper into the lungs, and is responsible for a lot of infant pneumonia. There is no vaccine.

Mumps virus is a member of the genus Paramyxovirus. It causes distinctive and generally benign system infections characterized by fever and parotitis (parotid inflammation, a salivary gland below the ear).

Epidemiology It is a disease of school-aged children worlwide. In unvaccinated populations, 92% of children have antibodies by age 15. A mumps vaccine was licensed in the U.S. in 1967, and it has reduced mumps infections to only 1,500 cases annually. Mumps is highly contagious. The virus infects epithelial cells of the upper respiratory tract, then spreads to regional lymphnodes. A viremia (bloodborne virion) spreads the virus to glandula and neural tissues.

Clinical Manifestations Up to 30% of mumps are asymptomatic. Symptoms include fever, malaise, and headache. After an 18 day replication phase of local replication and viremia, patients complain of ear pain and swollen salivary glands. CNS involvement is the most common extra-salivary manifestation, and occurs 10-30% of cases. It is 3-4 times more likely to occur in males than females for unknown reasons. Mumps CNS presents with high fever, vomiting, and headache lasting 48-96 hours. Maternal mumps infections during the first trimester of pregnancny may increase likelihood of spontaneous abortion.

Complications Mumps can effect gonads of both sexes. Testis inflammation (orchitis) is usually unilateral. Patients with mumps orchitis prsent with severe testicular pain and swelling, accompanied by high fever, nausea, vomiting, and headache. Testicular atrophy may follow orchitis in 35-50% of cases, but impotence or sterility is rare. Ovarian inflammation (oophoritis) occurs in 5% of postpubertal women with mumps. Patients typically report fever, nausea, and vomiting. Sequellae are uncommon, but impaired fertility can occur.

Prevention Children with mumps are usually isolated for 1 week after appearance of parotitis, even though this has dubious benefit since the virus is shed via respiratory secretions for several days before onset of clinical symptoms. In the U.S., the Jeryl-Lynn B strain of live virus is used for vaccination, following attenuation by serial passage in embryonated eggs. The mumps vaccine is a component of the MMR vaccine (measles, mumps, rubella).

Measles virus is a member of the genus Morbillivirus within the family Paramyxovirus. Measles virus differes from other members of the family in that it lacks neuraminidase. There is only one measles serotype, so recovery from natural infection confers lifelong immunity. Measles is one of five childhood exanthems, the others being rubella, varicella, roseola and fifth disease. Humans are the only known host for measles virus.

Epidemiology Measles is one of the most contagious human diseases. Vaccination has reduced the global incidence of measles, yet the World Health Organization reports there are still 45 million cases annually and 1.2 million deaths.

Transmission The principal mode of transmission is via large droplets of infected respiratory secretions inhaled during face-to-face exposure with coughing and sneezing individuals. This occurs during the catarrhal stage of the disease.

Pathogenesis Natural infection is initiated when measles virus reaches epithelial cells in the respiratory tract, oropharynx, or conjuctivae. During the first 2-4 days, the virus replicates locally and spreads via macrophages to draining lymph nodes, where further replication occurs. The virus then enters the bloodstream, producing a 1º viremia that spreads the virus throughout the reticuloendothelial system. Lymphoid hyperplasia occurs, and giant cells form due to cell fusion promoted by viral proteins. Further replication at these sites occurs, producing a secondary viremia of increasing magnitude that begins 5-7 days post-infection and spreads the virus to tissues throughout the body. During this 2 viremia, the virus is carried within leukocytes, more than 5% of which may be infected.

Clinical Manifestations Measles virus infection is rarely subclinical. The initial incubation period is clinically silent. Slight fever, malaise, and faint rash may occur in primary viremia. The prodromal stage of measles begin 8-12 days post-infect with fever, malaise, and anorexia followed by coryza (acute nasal congestion caused by secretion of mucus), conjunctivitis, sneezing, and cough. Catarrhal symptoms increase in intensity on or about the 5^th day. Coryza is intense, with profuse mucopurulent nasal discharge. There is palpebral conjuctivitis with lacrimation (abnormal and abundant shedding of tears). Severe coughing with a brass, barky quality ensues. 2-3 days before onset of rash, Koplik’s spots appear on inside of mouth. Kolplik describe them as 1-3 mm small irregular bright red spots with a minute bluish white speck at center. The rash begins 3-4 days after prodromal symptoms. The lesions appear behind the ear, on the forehead and on the upper part of the neck. They spread downward over the face, neck, and extremities, reaching the feet by the 3^rd day.

Clinical Diagnosis Measles can be diagnosed by isolates virus in cell culture from respiratory secretions, nasopharyngeal and conjuctiva swabs, PBMC, and urine as well as tissue biopsies. One can see giant cells characteristic of measles virus infection, or use specific antisera RT-PCR of the RNA.

Treatment Treatment of uncomplicated measles is symptomatic and includes bed rest, hydration, and antipyretics as needed. There is no antiviral therapy. The MMRV viaccine or a monovalent MV vaccine is used.