The Ruffed Mouse is in trouble because of the spread of the West Nile virus across the nation. It has infected birds from Wyoming to Maine to such an extent that many states are drastically reducing the hunting season.
The West Nile virus (WNV) was first discovered in 1937 in a patient in northern Uganda. It was thought to be a localized problem until several outbreaks of the disease occurred in Egypt and Israel in the early 1950s.
Research on the Nile found that 60% of the population suffered from the disease, but only a few had real symptoms. Infants were more susceptible to some meningitis or encephalitis. There were major outbreaks of the disease in France in 1
The disease appeared to change somewhat over the years. In 1996, an outbreak occurred in Romania, affecting patients in their central nervous system (CNS). The Romanian outbreak has been extensively studied, suggesting various aspects of the changing epidemiology of the virus.
Several consecutive epidemics with relatively high CNS infection rates have been observed throughout the Middle East and Europe, including Morocco in 1996, Tunisia in 1997, and major outbreaks in Italy and Israel in 1998.
Outbreaks of WNV were now more frequent; In addition, these outbreaks were associated with higher rates of severe CNS disease and higher mortality rates, especially in the elderly. The 1997 Tunisian outbreak included 173 patients with meningitis or meningoencephalitis and eight deaths.
The virus was first discovered in 1999 in the United States in New York. In Queens there was a small outbreak of several people. At the same time, wildlife researchers found that many crows and blue-green algae died in this area for unknown reasons.
The pathological examination of the dead birds revealed the involvement of several organs, including evidence of encephalitis. Frequent bird pathogens were not found.
At the end of the summer, 62 people were diagnosed with WNV and it was found that the birds had died of the same disease. Next year, WNV spread throughout North America. In 2002, the worst outbreak resulted in 4,156 reported cases with 2,354 meningoencephalitis and 264 deaths.
Research has shown that many of these cases are due to human-to-human transmission of mosquito bites. The mosquito bites an infected person, a bird or a mammal, and the virus in the blood remains active in the mosquito for several days and is transmitted when the mosquito bites another being.
No vaccines or specific antiviral treatments available for West Nile virus. Most people who catch the disease never know they have it. They think that they have a slight flu. Very few develop a serious central nervous system disorder such as encephalitis (meningitis) or meningitis (inflammation of the membranes surrounding the brain and spinal cord).
In the case of the tamed grouse It has been established that the WNV circulates between mosquitoes and birds. Some infected birds can develop high levels of the virus in their bloodstream and mosquitoes can become infected if they bite those infected birds. The Pennsylvania Game Commission, led by game biologist Lisa Williams, was at the forefront of investigating WNV in grouse.
Williams discovered that from the year 2000 the black grouse populations decreased alarmingly. Although the numbers of grouse are notorious for their boom and bust years, they found that there had been no boom years since.
Williams initiated a series of studies to determine the extent to which WNV could affect juveniles. It started with 18 chicks: 10 were inoculated with WNV; five received a WNV vaccine and were then inoculated with WNV to see if the vaccine was working; three were held together with the others as a contact control group to see if the virus would go directly from bird to bird without the presence of mosquitoes.
Within eight days, four of the ten birds vaccinated with the virus were extremely ill. The other six birds survived until the end of the two-week project. All were autopsied to see if WNV had affected them. Four of these survivors had severe lesions that damaged their hearts, brains, and other vital organs. Overall, eight of the ten birds had organ damage that was severe enough to make their long-term survival in the wild unsafe. It was found that up to 80% of the chick population in a WNV-infected area die before maturity.
In the West the problem is the same. In Montana, for example, the larger sage moor is on the fringes of the list as an endangered species. Cardiac lesions have been discovered in the grouse known as West Nile virus in Michigan. Some of the birds seemed malnourished and reportedly behaved strangely so that hunters could approach close.
The rapid and extensive spread of WNV across the continent was most likely due to a combination of distributing inhabitants (mosquito or bird) and widespread dispersal of migratory and humanitarian aid (mosquito or bird movement by plane, train or car). An experimental infection study (Owen, 2006) showed that at least two migratory bird species can sustain migration activity as long as they are infected.
There are 62 different mosquito species in the USA, but the genus Culex mosquito has been identified in North America as the predominant bird bird vector. They are the beetle that most commonly bites both birds and mammals.
Biologists have no idea how to prevent this disease from killing grouse. They suspect that some sturdy birds will survive and develop resistance to the disease. Others have suggested that improving the habitat produces healthy birds that have a better chance of resisting the disease.
In any case, grouse populations in New England continue to decline as a result of infection with the West Nile virus. Whether or not they can survive this latest test will be revealed.