a) Zoonosis is a normal disease of animals that can be transferred to humans with or without the help of diverse vectors.  b) Vectors are living transporters of infectious agents. They can transfer infectious agents like bacteria, viruses and protozoans to other animals and humans. Popular vectors are parasitic arthropods and domestic animals. c) Arthropod-borne diseases are diseases caused by infectious agents that arthropods served as vectors. Arthropods are invertebrate animals which have segmented bodies, possess exoskeletons and have jointed limbs. Some examples are arachnids, insects and crustaceans. d) Reservior hosts are main hosts of an infectious agent but they do not manifest the clinical symptoms of the disease and they can transfer the infectious agent to other animal hosts.
The ecological factors involved in the efficacy of WNV transmission to humans include climate change alterations in temperature abundance of avian species reservoir and, increased numbers of vectors.  Temperature is among the factors that highly influence the transmission and propagation of viruses in their different hosts. The alterations of temperature to that of the optimal temperature for transmission and replication of the virus can increase the incidence and intensity of disease.  Vast numbers of avian species reservoir and insect vectors could also magnify disease outbreaks.
The crow or Corvus spp. is an ideal indicator of West Nile Virus (WNV) to humans because of four reasons. First, they are easily infected by this virus and these infections have a high mortality rate. Second, crows are everywhere and they can be easily identified. Third, they are major sources of WNV infections because the virus intensively multiplies in the crows blood making it easy for mosquitoes to contact the virus and then infect humans. And fourth, its convenient to collect samples from crows because it does not consume any resources and great amount of time.
In order to calculate the point and interval approximations of WNV disease risk in an indivuals  country residence based on DCD 0.1 (dead crows per square mile), the Cochran-Mantel-Haenszel (CMH) option of the freq procedure in SAS System for Windows V8 was employed.  Comparison of WNV incidence risk between the areas with DCD reports and those without DCD reports was made through the application of CMH chi-square statistic. Since it takes about 2-14 days before WNV infection will manifest in human hosts, detach computations of CMH-pooled risk estimates for 3 exposure periods were done. These 3 exposure periods are two weeks prior to, one week prior to and the week of observance of WNV human cases.
Real time monitoring can be advantageous to the prevention of disease outbreaks. The information generated from this system can signal the prompt employment of numerous measures to prevent disease outbreaks in humans. On the other hand, real time disease monitoring is a very complexed system and various variables can influence its effectiveness.  Any negative influence from the variables involved can be detrimental to the systems effectiveness.  An example is its dependence on voluntary reports only, if absence of participants to report the sightings of dead crows occurs in a certain area, this would translate to failure of WNV human infection risk prediction in that area.
The factors that play a role in limiting the effectiveness of the Dead Crow Density (DCD) index as a predictor of potential human transmission cases are the variations in disease vector among the areas involved and the area residents participation in the reporting of the dead crow. Disease vectors are important in the zoonoses, transfer of infectious disease from animals to humans. Significant reduction in the number of vectors involve can also significantly lower the disease incidence and intensity. One limitation of DCD index then is its failure to consider the role of vectors in the transmission of disease. To reduce the impact of vectors in the study, a calculation variable for vectors could be included in the statistical analysis. Another limiting factor is the participation of people in reporting the sightings of dead crows. Low reporting participants translate into low specificity of the calculations. Hence, a solution is to educate and encourage the people to partake in the reporting.
The absence of reported human disease infections after a DCD e 0.1 can be due to vector variables or the human infections did not progress into a disease. Mosquitoes, which are vectors of the virus, might have been previously eliminated by mosquito control procedures. It is also possible that the mosquitoes did not feed on humans but instead fed on other animals. Another reason is not all viral infections lead to a clinical disease. Other infections only manifest as mild forms which are often undetected. Various factors like the high capability of the human hosts immune system can play a role in disease development.
Real time reporting systems like DCD index have great potential for the management of infectious diseases outbreaks. The establishment of real time reporting systems for other diseases can be of great significance to the health industry.  Given the time before the disease is transferred from the animal host to humans, various preventive and management measures can be prepared to minimize or eliminate the occurrence of infectious disease outbreaks in humans.


Post a Comment