From the infectious diseases meeting: What’s with the vaccine-o-phobia?

PHILADELPHIA – For the folks who promote vaccination, these are trying times. Recently, CNN hosted a segment titled: “Virus or Vaccine: Which is Worse?”

It’s enough to set Paul Offit to ranting, which he did this week at a meeting of the Infectious Diseases Society of America. Offit, a physician who heads the infectious disease division at Children’s Hospital of Philadelphia, has devoted a career to fighting illness. In his job, vaccines are often the most reliable weapon available, and cost-effective to boot. And although it’s astonishingly more dangerous to contract a disease than it is to get vaccinated for it, that message seems to have gotten lost somewhere along the way.

Offit traces this detour back to 1982, when DPT — the shot that prevents diphtheria, tetanus and pertussis – was (wrongly) linked to brain damage. “Three people believed their kids were harmed by the vaccine,” he says.

Offit has compassion for families who have a child who has suffered, whatever the cause may be, known or unknown. But since 1982, it’s been one accusation after another against vaccines. People tried to link the HIB vaccine to diabetes (no evidence), the hepatitis B vaccine to multiple sclerosis (all but one study found no link), and other vaccines to SIDS or autism. Recently, the HPV vaccine — which prevents cervical cancer – got linked to heart attacks and strokes (no proof).

And now the seasonal flu vaccine and H1N1 flu vaccine are being skipped by millions of people who somehow distrust the science that went into making them, even though the illnesses they cause can be fatal. Read more »

H5N1 (avian / bird flu) pandemic educational information

One of the primary concerns is that the virus could quickly spread across countries as various birds follow their migration routes. In response, countries have begun planning in anticipation of an outbreak. While short-term strategies to deal with an outbreak focus on limiting travel and culling and vaccinating poultry, long-term strategies require substantial changes in the lifestyles of the most at-risk populations.

WHO announced on November, 16, 2005 that an outbreak is most likely to hit the Hong Kong Special Administrative issue by mid-December of this year. “If it were to hit in a highly residential area like Tin Hau, it would be sure to spread like wildfire.” Dr. N Column, Head of Epidemic Prevention announced.

The WHO divides a pandemic into six phases, ranging from minimal risk of an outbreak to full scale pandemic. Most health authorities categorize the situation as of 2005 at Phase 3, by which is meant that human infections of a new sub-type has occurred but there is little evidence of sustained human-to-human transmission.

Avian Influenza (Bird Flu)

Avian influenza, or �bird flu�, is a contagious disease of animals caused by viruses that normally infect only birds and, less commonly, pigs. Avian influenza viruses are highly species-specific, but have, on rare occasions, crossed the species barrier to infect humans.

In domestic poultry, infection with avian influenza viruses causes two main forms of disease. The so-called �low pathogenic� form commonly causes only mild symptoms (ruffled feathers, a drop in egg production) and may easily go undetected. The highly pathogenic form is far more dramatic. It spreads very rapidly through poultry flocks, causes disease affecting multiple internal organs, and has a mortality that can approach 100%, often within 48 hours.

Influenza A viruses have 16 H subtypes and 9 N subtypes. Only viruses of the H5 and H7 subtypes are known to cause the highly pathogenic form of the disease. On present understanding, H5 and H7 viruses may circulate and infect poultry flocks in their low pathogenic form. The viruses can then mutate, usually within a few months, into the highly pathogenic form. This is why the presence of an H5 or H7 virus in poultry is always cause for concern, even when the initial signs of infection are mild. Read more »

Malaria

Background
Malaria, which predominantly occurs in tropical areas, is a potentially life-threatening disease caused by infection with Plasmodium protozoa transmitted by an infective female Anopheles mosquito vector. Individuals with malaria may present with fever and a wide range of symptoms.

The 4 Plasmodium species known to cause malaria include Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. A fifth species, Plasmodium knowlesi, has recently been identified as a clinically significant pathogen in humans. Timely identification of the infecting species is extremely important, as P falciparum infection can be fatal and is often resistant to standard chloroquine treatment. In some cases, individuals with malaria are infected with multiple Plasmodium species. P falciparum and P vivax are responsible for most new infections. Each Plasmodium species has a defined area of endemicity, although geographic overlap is common. Species can usually be distinguished by morphology on a blood smear. P falciparum is distinguished from the rest of plasmodia by its high level of parasitemia and the banana shape of its gametocytes.

Malaria in travelers typically manifests weeks after the individual leaves the endemic area. Presentation more than 4 weeks after returning from the endemic area is unusual. In some individuals, disease manifests months or years later, usually due to the presence of P vivax or P ovale hypnozoites, which can remain dormant in the liver and reactivate years after infection. Relapse with P vivax or P ovale infection is rare more than 5 years after initial infection. Because symptomatic delay is common, history of even a remote exposure to an endemic area should be elicited. Symptoms of malaria are nonspecific, and, because timely diagnosis and treatment are necessary, malaria should be considered in all patients from tropical areas who present with fever. Read more »

Dengue Fever

Background
Dengue, the most common arboviral illness transmitted worldwide, is caused by infection with 1 of the 4 serotypes of dengue virus, family Flaviviridae, genus Flavivirus (single-stranded nonsegmented RNA viruses). Dengue is transmitted by mosquitoes of the genus Aedes, which are widely distributed in subtropical and tropical areas of the world, and is classified as a major global health threat by the World Health Organization (WHO).

Initial dengue infection may be asymptomatic (50%-90%), may result in a nonspecific febrile illness, or may produce the symptom complex of classic dengue fever (DF). A small percentage of persons who have previously been infected by one dengue serotype develop bleeding and endothelial leak upon infection with another dengue serotype. This syndrome is termed dengue hemorrhagic fever (DHF), although dengue vasculopathy has been proposed as a better term, as fluid loss into tissue spaces can lead to prolonged shock and complications, including gastrointestinal bleeding, a greater fatality risk than bleeding per se. Some patients with dengue hemorrhagic fever develop shock (dengue shock syndrome [DSS]), which may cause death.

Dengue virus transmission follows two general patterns—epidemic dengue and hyperendemic dengue. Epidemic dengue transmission occurs when dengue virus is introduced into a region as an isolated event that involves a single viral strain. If the number of vectors and susceptible pediatric and adult hosts is sufficient, explosive transmission can occur, with an infection incidence of 25%-50%. Mosquito-control efforts, changes in weather, and herd immunity contribute to the control of these epidemics. Transmission appears to begin in urban centers and then spreads to the rest of a country. This is the current pattern of transmission in parts of Africa and South America, areas of Asia where the virus has reemerged, and small island nations. Travelers to these areas are at increased risk of acquiring dengue during these periods of epidemic transmission.

Hyperendemic dengue transmission is characterized by the continuous circulation of multiple viral serotypes in an area where a large pool of susceptible hosts and a competent vector (with or without seasonal variation) are constantly present. This is the predominant pattern of global transmission. In these populations, antibody prevalence increases with age and most adults are immune. Hyperendemic transmission appears to be a major risk for dengue hemorrhagic fever. Travelers to these areas are more likely to be infected than are travelers to areas that experience only epidemic transmission. Read more »

Influenza

Background
Influenza virus infection, one of the most common infectious diseases, is a highly contagious airborne disease that causes an acute febrile illness and results in variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death. These symptoms contribute to significant loss of workdays, human suffering, mortality, and significant morbidity. The 1918-1919 H1N1 type influenza pandemic killed an estimated 20-50 million persons, with 549,000 deaths in the United States alone.

Accurately diagnosing influenza A or B infection based solely on clinical criteria is difficult because of the overlapping symptoms caused by the various viruses associated with upper respiratory tract infection (URTI). In addition, several serious viruses, including adenoviruses, enteroviruses, and paramyxoviruses, may initially cause influenzalike symptoms. The early presentation of mild or moderate cases of flavivirus infections (eg, dengue) may initially mimic influenza. For example, some cases of West Nile fever acquired in New York in 1999 were clinically misdiagnosed as influenza.

Patients with influenza frequently present with various symptoms shared by many other viral infections. In the northern and southern hemispheres, these symptoms are more common in the winter months. As a result, during the winter, clinics and emergency department waiting rooms fill with patients who have influenza or other URTIs.
Pathophysiology
Influenza results from infection with 1 of 3 basic types of influenza virus—A, B, or C—which are classified within the family Orthomyxoviridae. These single-stranded RNA viruses are structurally and biologically similar but vary antigenically.

The RNA core consists of 8 gene segments surrounded by a coat of 10 (influenza A) or 11 (influenza B) proteins. Immunologically, the most significant surface proteins include hemagglutinin and neuraminidase. The viruses are typed based on these proteins. For example, influenza A subtype H3N2 expresses hemagglutinin 3 and neuraminidase 2.

The most common prevailing influenza A subtypes that infect humans are H1N1 and H3N2. Each year, the trivalent vaccine used worldwide contains A strains from H1N1 and H3N2, along with an influenza B strain.

Influenza virus infection occurs after transfer of respiratory secretions from an infected individual to a person who is immunologically susceptible. If not neutralized by secretory antibodies, the virus invades airway and respiratory tract cells. Once within host cells, cellular dysfunction and degeneration occur, along with viral replication and release of viral progeny. Systemic symptoms result from inflammatory mediators, similar to other viruses. The incubation period of influenza ranges from 18-72 hours.

Influenza A is generally more pathogenic than influenza B. Influenza A is a zoonotic infection, and more than 100 types of influenza A infect most species of birds, pigs, horses, dogs and seals. Indeed, the 1918 pandemic that resulted in millions of human deaths worldwide is believed to have originated from a virulent strain of H1N1 from pigs or birds. Recently, scientists obtained and sequenced the 1918 H1N1 strain from a frozen corpse found in Alaska. The virus was reconstructed at the Centers for Disease Control and Prevention (CDC) laboratory in Atlanta and was found to be highly lethal when tested in mice; the virus was also found to be lethal to chicken embryos. This unique N1 neuraminidase is being studied in order to provide better insight into the N1 found in H5N1, the type responsible for avian influenza (also known as bird flu). Read more »