19 August 2012

West Nile Virus Claims 26 Lives!

 - 693 Cases reported in 43 U.S. States! As of August 14, 2012, the West Nile Virus has been reported in people, birds, and mosquitoes. Of these, 406 (59%) cases were classified as neuroinvasive disease (such as meningitis or encephalitis) and 287 (41%) were classified as non-neuroinvasive disease. This is the report from the CDC who has said that this is the biggest infection rate ever.

 - Furthermore, over 80 percent of the cases have been reported from just six states (Texas, Mississippi, Louisiana, Oklahoma, South Dakota, and California) and almost half of all cases have been reported from Texas. For a state-by-state ArboNet case count please check their infographic here 

 - Why this epidemic has gotten this widespread is probably multi-factorial. Because of changes in weather, the environment has facilitated the infestation of mosquitoes. Alternating dry and damp weather, stagnant water pools and other similar breeding grounds abound. In most species, adult females lay their eggs in standing water; some lay eggs near the water's edge; others attach their eggs to aquatic plants. Each species selects the situation of the water into which it lays its eggs and does so according to its own ecological adaptations.  

 - Although this is known to be a summer problem, it does continue into the fall. The heat as well has contributed, as dust and other minute particles are whipped up into the atmosphere thereby spreading more infectious material. Those familiar with the desert areas know about dust devils which also begin at boundaries between semi-dry soil and powdery sand. A warm temperature in the area creates conditions favorable for these whirlwind phenomena. Culex mosquitoes, still considered the main vectors, spend the winter hibernating in protected structures such as root cellars, bank barns, caves, abandoned tunnels and other subterranean locations.

 - West Nile virus (WNV) belongs to  Group IV ((+)ssRNA), Family: Flaviviridae, Genus: Flavivirusis,  and is one of the Japanese encephalitis (JE) antigenic serocomplex of viruses. The flaviviruses comprise more than 70 members including important human pathogens such as yellow fever virus, dengue virus, and West Nile virus. The structures of two flaviviruses, dengue and West Nile virus, have been solved by cryo-EM and image reconstruction techniques and have been shown to be similar.

 - In WNV,  image reconstructions and cryo-electron microscopy  reveal a 45–50 nm virion covered with a relatively smooth protein surface. The flavivirus virion is made up of three structural proteins: capsid (C), pre-membrane (prM), and envelope (E) that are translated from the 5’ one-third of the RNA genome. The genetic material of WNV is a positive-sense, single strand of RNA, which is between 11,000 and 12,000 nucleotides long. These genes encode seven nonstructural proteins and three structural proteins. The RNA strand is held within a nucleocapsid formed from 12-kDa protein blocks; the capsid is contained within a host-derived membrane altered by two viral glycoproteins.  

 Electron microscopy of West Nile virus, taken from lab, 
rights retained to displayed author.
Original uploader was PhD Dre at en.wikipedia 
Permission: CC-BY-SA-3.0,2.5,2.0,1.0;
 Released under the GNU Free Documentation License.

  - Some characteristics of viruses differ on close examination by imaging. 
Non-enveloped viruses provide model systems for high-resolution structural study of whole virus capsids (and their components) and the principles of large-scale nucleo-protein tertiary and quaternary interactions. In many cases, they are relatively small, stable, and highly symmetric particles that can be purified as homogeneous samples inlarge quantities. These properties make them suitable for the techniques of X-ray crystallography, X-ray fiber diffraction, and cryoelectron microscopy (cryo-EM) combined with image reconstruction. Enveloped virus particles generally have greater flexibility and asymmetry, two features that inhibit application of high-resolution techniques.

 - Flaviviruses  enter  cells  via  receptor-mediated endocytosis. It is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, crocodiles and alligators. To survey the area of coverage of the infection, the approach would be to use the blood sera of wild birds and sentinel chickens. Samples must be tested for the presence of WNV antibodies by use of immunohistochemistry (IHC : see Image of the Week below) or Enzyme-Linked Immunosorbent Assay (ELISA).  Dead birds, after necropsy, have their various tissues tested for virus by either RT-PCR (Reversetranscription polymerase chain reaction) or IHC , where virus shows up as brown-stained tissue because of a substrate-enzyme reaction. Pioneer experiments with RNA bacteriophages showed high levels of genetic variability, suggesting error-prone replication and, later on, RNA viruses were confirmed to show high per-base mutation rates and short genomes. RNA viruses critically rely on fast replication for survival. Their rapid infection cycles allow them to reach high titers before the onset of host defense mechanisms.

 - About one in 150 people infected with WNV will develop severe illness. The disease presents with symptoms that consist of high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. The neurologic picture may be permanent in these affected individuals. Apparently, the ratio of severe disease is low. But who gets it may be explained by the location of the individual, surrounding environment, and possibly a lowered immune response. In some people the illness is mild fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Duration of illness is shorter but even apparently health people may suffer. In 80% of the cases it is basically an asymptomatic illness.

 - As mentioned above, WNV is spread by the bite of an infected mosquito. The infected mosquito species vary according to geographical area. In the US, Culex pipiens (Eastern US) the common house mosquito, Culex tarsalis (Midwest and West), and Culex quinquefasciatus (Southeast) are the main sources.  A. albopictus mosquito (Asian tiger mosquito) - an invasive species in North America - is a vector of various diseases including the West Nile virus. West Nile virus can be sampled from the environment by the pooling of trapped mosquitoes, testing avian blood samples drawn from wild birds, dogs and sentinel monkeys, as well as testing brains of dead birds found by various animal control agencies and the public. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite. Tissue transfer like blood transfusions and organ transplant may also be channels of spread. Mother-to-fetus transfer may also occur. It is not spread by touch.

 - There is no vaccine for humans. A vaccine for horses (ATCvet code: QI05AA10) based on killed viruses exists; some zoos have given this vaccine to their birds, although its effectiveness is unknown. Dogs and cats show few if any signs of infection. There have been no known cases of direct canine-human or feline-human transmission; although these pets can become infected, it is unlikely they are, in turn, capable of infecting native mosquitoes and thus continuing the disease cycle. Unlike malaria where one might take tablets for prophylaxis before entering a high-risk area, there exists no oral drug equivalent for WNV.

 - So, there are a few important guidelines to halt or minimize the spread of infection. These consist of using EPA approved mosquito repellant such as N,N-Diethyl-meta-toluamide  (DEET) intended to be applied to the skin or to clothing, draining or disposing of stagnant water silos or puddles, as well as avoiding slow running streams or swamps. Spraying of insecticides in hotspots could also be carried out. Of course, this may pollute the environment. If the EPA can make available an organic chemical that is harmless to animals then that would be a more environment-friendly solution. Aside from staying indoors, wear long-covering clothing, apply bug repellant that contains DEET, and ensure mosquitoes cannot enter buildings. Those who plan to travel to risky environments ought to arm themselves with the pesticide, in addition to long protective clothing. Community members and volunteers of said areas who are responsible for cleaning up their locales must be prepared just the same.

 - A person may start manifesting the illness between 3 to 14 days. There is no specific treatment except for supportive therapy. People who suspect they may have WNV infection should report to the hospital where they will be evaluated by health professionals. If you are over 50 years of age and linger outdoors then you are at a higher risk for the infection. So as soon as there’s a fever and unusually severe headaches the recourse is to go to hospital where you can get the best needed support. For further info and CDC resources kindly visit this page. So one must remember, if in a risky environment, stay indoors, and close all windows. If windows have screens make sure they are in order. Before going outdoors, apply an EPA and FDA approved mosquito repellant. A suggestion would be to use citronella oil. Citronella oil is also a renowned plant-based insect repellent, and has been registered for this use in the United States since 1948. At any rate, if anyone develops a febrile malaise, it is best not delaying to report to hospital as soon as possible.

 - Note that interesting cases of hoaxes for outbreaks have occurred. In 1999, an article appeared suggesting that the CIA was investigating whether Iraq was responsible for causing the outbreak of West Nile fever in the New York City area. The story relied heavily on a previous story written by an Iraqi defector, claiming that Saddam Hussein planned to use WestNile virus strain SV 1417 to mount an attack. The investigation indicated that there was no known evidence of bioterrorism involved in the spread of West Nile virus. But one of the largest bioterrorism hoaxes occurred in 2000. According to e-mail messages widely circulated on the Internet, an organization known as the Klingerman Foundation was mailing blue envelopes containing sponges contaminated with a fictional pathogen called the ‘Klingerman virus’. According to the e-mail alert, 23 people had been infected with the virus, including 7 who died.

 >>> Watch You Tube video here!

>>>  For more videos on West Nile Virus, scroll down to the Video Bar below!

 - For a catalog of viruses, you can visit the pages at Medpedia or MeSH.

- Take care. This is it for now. Any new info will follow. 

- Fernando Yaakov Lalana, M.D.

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