The Ruffed grouse is in trouble all across the nation as a result of the spread of the West Nile Virus. It has infected birds from Wyoming to Maine to such a degree that many states have or are considering drastically reducing hunting seasons.
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 early in the 1950‘s several outbreaks of the disease happened in Egypt and Israel.
Surveys along the Nile River found that as many as 60% of the population had the disease in their bodies, but only a few had any real symptoms. Young children were more susceptible with some contracting either meningitis or encephalitis. There were large outbreaks of the disease in France in 1962 and in South Africa in 1974.
The disease seemed to change a bit over the years. In 1996 an outbreak in Romania saw patients affected in their central nervous system (CNS). The Romanian outbreak was extensively studied and suggested several things about the changing epidemiology of the virus.
Several subsequent epidemics associated with relatively high rates of CNS infection were observed throughout the Middle East and Europe, including Morocco in 1996, Tunisia in 1997, and large outbreaks in Italy and Israel in 1998.
Outbreaks of WNV were now occurring more frequently; in addition, these outbreaks were associated with higher rates of severe CNS disease and higher fatality rates, predominantly among older individuals. The Tunisian outbreak of 1997 involved 173 patients hospitalized with meningitis or meningoencephalitis, and eight deaths.
The virus was first detected in the United States in New York City in 1999. There was a small outbreak of several persons in Queens. At that same time, wildlife researchers noted that many crows and bluejays in the area were dying from an unknown cause.
Pathologic assessment of the dead birds displayed involvement of multiple organs, including evidence of encephalitis. Common avian pathogens, however, were not detected.
By the end of the summer, 62 people were diagnosed with WNV and it was determined that the birds had died of the same disease. By the next year the WNV was spreading throughout North America. In 2002, the worst outbreak ever resulted in 4,156 reported cases with 2,354 of meningoencephalitis and 264 deaths.
Research indicated that many of these cases were the result of the disease being passed from human to human through mosquito bites. The mosquito bites an infected person, bird, or mammal, and the virus in the blood stays active for several days in the mosquito and is transmitted when the mosquito bites another being.
To date there are no vaccines or specific antiviral treatments for West Nile Virus available. Most people who get infected with the disease never know they have it. They think they have a mild case of the flu. Only a very few develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).
In the case of the ruffed grouse, it was found that the WNV cycles between mosquitoes and birds. Some infected birds can develop high levels of the virus in their bloodstream and mosquitoes can become infected by biting these infected birds. The Pennsylvania Game Commission, under the leadership of Game Biologist Lisa Williams, has been in the forefront of studying WNV in grouse.
Williams discovered that starting in the year 2000 the grouse populations began to decline at an alarming rate. Although grouse numbers have been notorious for their boom and bust years, she noted that there has been no boom years since then.
Williams initiated a series of studies to determine the extent to which WNV could affect young birds. She started with 18 chicks: 10 were inoculated with WNV; five were given a WNV vaccine and then inoculated with WNV to see if the vaccine worked; three were housed with the others as a contact control group to see if the virus would pass directly from bird-to-bird without the presence of mosquitoes.
Within eight days, four of the 10 birds inoculated with the virus were extremely ill. The other six birds survived to 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. In total, eight of the 10 birds had organ damage severe enough to make their long-term survival in the wild uncertain. It has been found that as much as 80% of the chick population in a WNV infected area die before maturity.
Out west the problem is the same. In Montana, for example, the greater sage grouse is on the edge of being listed as an endangered species. In the grouse testing positive for West Nile Virus in Michigan, heart lesions were discovered. Some of the birds appeared malnourished and reportedly acted strangely, allowing hunters to approach closely.
The rapid and extensive spread of WNV across the continent most likely occurred through a combination of dispersing residents (mosquito or bird) and long-distance spread with migrating birds and human help (mosquito or bird movement by plane, train, or automobile). An experimental infection study (Owen, 2006) demonstrated that at least two migratory bird species can maintain migratory activity while infected.
There are 62 different species of mosquitos in the United States, but the genus Culex mosquito that has been identified as the predominant bird-to-bird vector across North America. They are the bug that most often will bite both birds and mammals.
Biologists have no idea at this point how to prevent this disease from killing grouse. They surmise that some hardy birds will survive and will develop a resistance to the disease. Others have suggested that improving habitat produces healthy birds, which have a better chance of resisting the disease.
In any case, the grouse populations in New England are continuing to decline as a result of being infected with the West Nile Virus. Whether or not they can survive this latest test is yet to be seen.