MEDICAL SURFARI; MOSQUITOES MAY SPREAD DISEASE

Recently, in New York City dead crows were discovered, and the Bronx Zoo began losing some of its birds in captivity. Initially this was very perplexing, but tests on these birds, and a New York City resident who died recently, confirmed that some birds and mosquitoes in the New York City and Connecticut area are infected with a West Nile-like virus. This has resulted in a human encephalitis outbreak in that area. Some mosquitoes and birds continue to harbor this virus; however, the prevalence at this time is not fully determined. Nevertheless, many precautions and eradication measures are under way there to prevent further transmission and toll of this disease.

The West Nile virus is closely related to the St. Louis encephalitis virus, and both are transmitted by the same mosquito species. Although human beings, birds and mosquitoes can become infected with these viruses, they are only transmitted by mosquitoes that have fed upon infected birds. The West Nile-like virus is not transmitted from person to person or from birds to people. At this point, it is not clear how the West Nile-like virus made its way to the western hemisphere, and especially the United States, as it has never before been recognized here.

There are many different types of organisms that may cause inflammation or infection of the brain and its surrounding membranes. Generally, when one becomes ill from a viral infection of the brain, this is called encephalitis; whereas, when a highly destructive bacterial infection of the brain occurs, preceding abscess formation, this is called cerebritis. Each of these conditions may cause diffuse or focal encephalopathy (abnormal brain function).

There are many different viruses that may cause encephalitis, and each requires a portal of entry into the body and ultimately into the brain. Some viruses are transmitted by human beings, and others by mosquitoes or ticks that inoculate their victim with an arbovirus. Rabies is also caused by a virus; however, this is generally transferred by an animal bite. Each of these viruses replicate outside of the brain and then gain entry either by spreading through the blood or along the nerves that connect to the brain. Once within the brain the virus enters the nerve cells, disrupting normal cell function and ultimately causing permanent injury or death.

All arboviruses require an insect to transmit the infection from one host to another and in the United States this is more likely to occur between June and October. Most of the viruses that cause encephalitis do not seem to have a predilection for men or women; however, they each seem to have a predilection for people of certain age groups. Generally individuals at the extremes of age are at the highest risk, and certainly anyone with a compromised immune system due to other illness is a prime victim.

Encephalitis causes encephalopathy and this often results in behavioral or personality changes, decreased consciousness, seizures, confusion or amnesia as well as headache and stiff neck.

The Centers for Disease Control have suggested that when outdoors, to reduce contact with mosquitoes, wear clothing that covers the skin such as long sleeves, shirts and pants and spray clothing and exposed skin with insect repellent. Curb activities outside at dawn, dusk and during the evening when mosquitoes tend to feed. Further, they recommend continuing individual and community efforts to control or prevent mosquito breeding.

Clinically, it is important to distinguish and quickly diagnose these conditions as each may cause permanent brain damage or even death. Swift identification and treatment may be lifesaving.

World Wide Web Resources

Centers for Disease Control and Prevention

www.cdc.gov/od/oc/media/pressrel/r990924.htm

This is the most recent press release from the CDC regarding the West Nile-like virus.

Dr. Scott Gibbs is a Cape Girardeau neurosurgeon and editor-in-chief of Mosby's Medical Surfari. You may e-mail questions to him at drgibbs@semissourian.com or write in care of the Southeast Missourian, P.O. Box 699, Cape Girardeau, Mo., 63702-0699.