Prediction of Modified Influenza A Virus Virulence in Humans Using Animal Models - Essay Example

The envelope has two surface glycoproteins called neuraminidase and hemagglutinin, the latter gets attached to the host cell before viral penetration. Often the HA protein undergoes several antigenic changes, such genomic alterations lead to phenotypic changes thus challenging the development of vaccines against influenza virus. [A. Maher and Joanne DeStefano]PATHOGENESISA virulent influenza A virus in humans is responsible for the infection of the respiratory tract leading to necrosis of the epithelial tissues.

The infection then extends to the bronchioles and alveoli resulting in interstitial pneumonia. A susceptibility to bacterial superinfection is not uncommon. The infection slowly affects extra respiratory tissues leading to myocarditis, myositis, parotitis, encephalopathy, and Reye-Jhonson syndrome. [T. Kuiken, G. F. Rimmelzwaan, G. Van Amerongen, and A. D. M. E. Osterhaus]HYPOTHESISFor most experimental studies concerned with animal models, the mouse is widely used. The low cost combined with its small size permits researchers to conduct large-scale studies.

The mouse is also considered suitable as a mammalian model for the studies concerning the pathogenesis and immunity of the human H5N1 influenza virus mainly because this virus replicates very effectively and efficiently in the lungs of mice without any adaptation. This hypothesis paves the way to investigate the mouse as a mammalian model to study human influenza virus infection and hence a novel approach can be employed for effective vaccination against the virus.METHODThe following method is suggested, based on available material on the subject.

Viral stocks should be propagated in the allantoic cavities of 10-day-old embryonated hen eggs under conditions that favor the replication of the H5N1 virus. Virus stocks should be aliquoted and stored at -70'c until use. Female BALB/C mice should be anesthetized with CO2 and 50 microlitres of infectious virus diluted in phosphate-buffered saline(PBS) should be inoculated intranasally. Fifty percent mouse infectious dose (MID 50) and fifty percent lethal dose (LD50) titers could be determined by inoculating groups of seven mice intranasally with a serial 10-fold dilution of the virus.

Four days later, Observe three mice from each group after euthanizing. Collect the lungs and let them homogenize in 1ml of cold PBS. Let the tissues be titrated for virus infectivity in eggs. The four remaining mice in each group should be checked daily for disease signs and death for 14 days post-infection. Replication of H5N1 viruses in mice is to be examined by determining the virus titers in organs(like lungs, spleen, liver, kidney, and brain) and blood 4 and 6 days post-infection with 100 MID50 of viruses.

Tissues from infected mice are to be formalin-fixed and processed using a two-step biotin-streptavidin method for histochemical analysis. Further examination can also be taken up for the presence of viral antigens in sub-epithelial tissues in the lungs. [Xiuhua Lu, Terrence M. Tumpey, Timothy Morken, Sherif R. Zaki, Nancy J. Cox, and Jacqueline M. Katz] However the major drawback with mouse lies with its size - since the small size of the mouse increases the difficulty of readily observing the clinical signs of the disease.

Another recommended animal model used to study the human influenza virus is the Ferret. This animal is prone to both avian and human influenza viral infections. Again, Ferrets have a long trachea and the upper and lower respiratory tracts can easily be compartmentalized making them ideal models for viral studies. Ferrets can also be used as models to study human GI tract disorders since they share similar anatomical and physiological natures concerning the stomach. Also, the carotenoid metabolism in ferrets is similar to that of humans as a result ferrets can serve as potent models in studies involving nutrition analysis.

The various clinical parameters like temperature, pulse, and respiratory rate can be easily measured considering the size of ferrets. [Fox et al. 1990]The disadvantages of using Ferrets as an experimental model include the higher cost of the animal, caging, and maintenance costs compared to that of mice. [A. Maher and Joanne DeStefano]Besides mice and ferrets, Squirrel monkeys can be a good choice for influenza virus studies, since most of their characteristics match that of humans. Squirrel monkey is also a good choice for Biomedical research since there is less risk of zoonotic disease transmission with this animal. Moreover, the personal protective equipment for handling squirrel monkeys is less extensive. The disadvantages in this case include availability, the need for trained personnel, and health risks like TB. Squirrel monkeys also entail associated costs with procuring and maintaining primates.