Double trouble: Bacterial super-infection after the flu
American Journal of Pathology
Public release date: 22-Jan-2010
Current research suggests that the flu may predispose to secondary bacterial infections, which account for a significant proportion of mortality during flu pandemics. The related report by Lee et al, “A mouse model of lethal synergism between influenza virus and Haemophilus influenzae,” appears in the February 2010 issue of The American Journal of Pathology.
Bacterial cells of Staphylococcus aureus, which is one of the causal agents of mastitis in dairy cows. Its large capsule protects the organism from attack by the cow’s immunological defenses. Magnified 50,000X. USDA.
Influenza affects between three and five million people annually, causing up to 500,000 deaths worldwide. While most people will recover in one to two weeks, others will develop life-threatening conditions such as pneumonia or bronchitis. High-risk groups for seasonal influenza include the very young and old, people with compromised immune systems, and pregnant women. However, during influenza pandemics, mortality may be significant in previously healthy young adults.
A common complication of flu infection is a secondary “super-infection” by bacteria, which greatly increases the morbidity and mortality of the disease. The most common bacterial agents found following flu pandemics have been Streptococcus pneumoniae, Haemophilus influenzae, Group A Streptococcus, and Staphylococcus aureus. Furthermore, reports of infection with antibiotic-resistant strains have been increasing in recent years.
To explore the mechanisms governing the increased pathogenesis of flu upon super-infection, a group led by Dr. Sally R. Sarawar of the Torrey Pines Institute for Molecular Studies, San Diego, California confirmed that otherwise nonlethal influenza and H. influenzae infections cause high mortality rates in mice when flu infection precedes H. influenzae infection. Their data confirm a restricted time period for this heightened susceptibility and highlight that excessive bacterial, and not viral, growth is associated with increased lethality. The fact that this increased mortality was observed in both immunocompromised and immunocompetent mice suggests that even normal healthy people are at increased risk for complications following bacterial super-infection.
Lee et al suggest that the “lethal synergy between influenza virus and the bacterial respiratory pathogen, H. influenzae, is mediated by innate immunity. They observed that severe damage to the airways was an early event in the co-infected mice, eventually leading to death. This underscores the need for early antiviral and antibiotic treatment to combat severe disease in human patients and highlights the importance of vaccination and effective hygiene measures to prevent secondary bacterial infections during influenza infection. This new model will be useful for further investigating the mechanisms underlying severe disease caused by the interaction between influenza virus and bacteria, which may have resulted in numerous deaths during influenza pandemics and continues to constitute a significant clinical problem in susceptible individuals.” Currently ongoing studies suggest that this model may also be useful for identifying target molecules for the development of novel therapeutic agents and strategies. [EoPR]
Note: Image and caption not included in the press release.
What is Staphylococcus aureus? [Source: CDC]
Staphylococcus aureus, often referred to simply as “staph,” is a bacteria commonly found on the skin and in the nose of healthy people. Occasionally, staphylococci can get into the body and cause an infection. This infection can be minor (such as pimples, boils, and other skin conditions) or serious and sometimes fatal (such as blood infections or pneumonia). Staph. aureus is a common organism and can be found in the nostrils of up to 30% of persons. Person-to-person transmission is the usual form of spread and occurs through contact with secretions from infected skin lesions, nasal discharge or spread via the hands.
What is MRSA?
MRSA are staphylococci that are resistant to the antibiotic, methicillin, and other commonly used antibiotics such as penicillin and cephalosporins. These germs have a unique gene that causes them to be unaffected by all but the highest concentrations of these antibiotics. Therefore, alternate antibiotics must be used to treat persons infected with MRSA. Vancomycin has been the most effective and reliable drug in these cases, but is used intravenously and is not effective for treatment of MRSA when taken by mouth.
Photomicrograph of Streptococcus pyogenes bacteria, 675x Mag. A pus specimen, viewed using Pappenheim’s stain. Last century, infections by S. pyogenes claimed many lives especially since the organism was the most important cause of puerperal fever and scarlet fever. This media comes from the Centers for Disease Control and Prevention’sPublic Health Image Library (PHIL), with identification number #2110.
More information on MRSA from CDC: Methicillin-resistant Staphylococcus aureus
In 2005, MRSA killed 19,000 people in the United States—more than 1.5 times as many people than died of AIDS that year.
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