What if there was a meningitis outbreak?

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1. I need to select one bacterial, one fungal, and one viral pathogen capable of producing menigitis in humans. (three pathogens)

Meningitis is an infection of the spinal cord and the brain that is caused by a bacterial infection, a viral pathogen, and sometime, a fungal infection. (1) The most common cause of meningitis is a bacterial infections that enter the bloodstream and migrate to the spinal cord and brain. (1)
One bacteria that can cause meningitis is streptococcus pneumoniae. This is a common bacterium that cause bacterial meningitis in infants, children, and adults in the US. It can cause pneumonia or ear infection. Fortunately, there is a vaccine to reduce the spread of this bacterial meningitis infection.

Viruses can also cause meningitis, and there is a greater number of cases of viral meningitis than bacterial meningitis. Unlike bacterial meningitis, viral meningitis are often mild and not life threatening. The group of viruses that cause meningitis are the enteroviruses. Viruses like West Nile virus can cause viral meningitis.

Fungus can also cause meningitis. Although fungus meningitis is very rare, it does occur in human. It is not contagious from person to person. A common fungal meningitis that affect people with AIDS is cryptococcal meningitis. It is cause by the fungus called Cryptococcus that is acquired by inhaling soil contaminate with bird droppings. (2)

2. Describe the general characteristics and structure of each pathogen.

General Characteristics:

A. Streptococcus pneumoniae

I. Morphology

Streptococcus pneumoniae is a nonmotile, non-spore forming, gram-positive coccus of the phylum S. pneumoniae that is also known as pneumococcus. They are look like "lancet-shaped cocci, which are elongated cocci with a slightly pointed outer curvature. (4) They can form pairs of cocci known as diplococci. They can occur in single or short chains. (4) They are nonmotile, and do not form spores. (4) They do not have catalase and ferment glucose to lactic acid. They have cell wall that contain peptidoglycan and teichoic acid.

II. Cultivation

Streptococcus pneumoniae grow best in 5% carbon dioxide and requires a source of catalase to neutralize the hydrogen peroxide produce by the bacteria. Pneumoccoci grow as glistening colonies on agar. They have two types of phase variation derived genetically; they can be opaque or transparent colonies. The transparent colonies are adapted to colonization of nasopharynx, whereas the opaque variant is suited for survival in the blood.
Streptococcus pneumoniae is a fermentative aerotolerant anaerobe that is cultured in media containing blood. They showed alpha (green) hemolysis when cultured on blood agar. Streptococcus pneumoniae is a fragile bacterium that contain enzymes known as autolysin that would disrupt the cells.

III. Identification

The identification of pneumococci from other streptococci are bile and optochin sensitivity, gram positive staining, and hemolytic activity. They cause alpha hemolysis on agar. They can switch to beta hemolysis under anaerobic conditions. They form a 16 mm zone of inhibition around 5 mg optochin disc and undergo lysis by bile salts. A few drops of 10% deoxycholate at 37C lyses the entire culture in minutes. For diagnostic purposes, a gram stain may be performed.

IV. Virulency

The capsule is responsible for their virulence. Since there are over 90 serotypes of S. pneumonia, it is very difficult to develop vaccine for this bacterium. (3) "S. pneumoniae is the leading cause of pneumonia in all ages." (3) S. pneumoniae caused the lung alveoli to fill up with serous fluid that mediate the spread of the bacteria throughout the lungs. Neutrophil that are attracted to the S. pneumoniae can invade the alveoli. Most neutrophils invade the alveoli. Macrophages come and eliminate the remaining residue from inflammatory response. When S. pseumoniae stayed in the lung, it can invade the blood and cause bacteremia. (3)

B. West Nile Virus

I. Morphology
Microscopy of the West Nile Virus revealed a spherical, enveloped capsid with a diameter of 45-50 nm and contains single stranded, positive sense RNA ( 11000-12000 nucleotides long) that encodes the capsid, envelope, and virion smooth protein surface, which is similar to dengue fever virus and belong to the genus Flavivirus with the family Flaviviridae. It has 7 nonstructural proteins that may contribute to viral replication. The genetic material of West Nile Virus is a positive-sense, single strand of RNA which is between 11,000 and 12,000 nucleotides long.

II. Identification

West Nile Virus is a positive strand RNA viruses that consists of a 11 kb genome encoding the protein capsid that surrounds a DNA core of positive sense single stranded RNA of about 10,000 bases. The capsid is contained within a spherical outer envelope of about 50 nanometers in diameter consisting of proteins, lipids, trace metals, and carbohydrate. ( 5) West Nile virus is an arbovirus, where the primary arthropod vector for West Nile is the ...