Smith Presentation Summary

Presentation Summary

Animal Diseases and Human Welfare

Gary Smith
School of Veterinary Medicine
University of Pennsylvania

Summary

Five diseases of wild and domesticated animals have received wide attention in recent years because of their impact on human welfare. These diseases are bovine spongiform encephalopathy, West Nile, foot and mouth, Lyme and anthrax. The diseases and their effects have been summarized below.

BOVINE SPONGIFORM ENCEPHALOPATHY

Bovine spongiform encephalopathy (BSE or mad cow disease) has been primarily a disease of dairy cattle. It has been responsible for the loss of 180,000 cattle in Great Britain since 1986 with profound economic and political consequences. The disease has occurred less frequently in many European countries but is unknown in the United States.

BSE is caused by a prion (an abnormal protein) transmitted in cattle feeds containing contaminated animal byproducts such as meat and bone meal. This prion is believed to cause a disease in humans when contaminated meat is consumed and is similar, but not identical to, Creutzfeldt-Jakob disease (CJD). The variant disease has been designated vCJD to distinguish it from the classical CJD that occurs infrequently but worldwide. The variant vCJD typically affects people less than 52 years of age, while the classical CJD affects people over 63 years old. There have been 107 cases of vCJD in England and the number of cases appears to be increasing each year. This same trend appears to be occurring in European countries. The prion responsible for BSE and vCJD causes proteins in infected cells to spiral in a reverse direction. This reaction renders the proteins insoluble and causes death of the invaded central nervous system cells.

BSE is being effectively controlled in England and Europe by prohibiting the use of meat and bone meal in cattle feeds. Because of the long incubation period of the prions, vCJD continues to appear in human populations in England and continental Europe. Prohibiting the importation and use of animal byproducts in cattle feeds has prevented the appearance of BSE in the United States but one case of BSE has been reported in Canada in a cow imported from England.

WEST NILE DISEASE

West Nile disease is a common disease of birds in Europe, Middle East, Central Asia and Africa caused by a mosquito-borne virus. The virus also attacks horses and people where it causes encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord) that may be fatal. Symptoms in humans vary, but a fever, headache, stiff neck and muscular pains are most common. West Nile virus was first observed in the United States in 1999 when 62 cases and 7 deaths occurred in the vicinity of New York City. In 2000 there were 21 cases and 2 deaths and 60 equine cases diagnosed. In 2001 there were 31 people diagnosed with the virus and 1 death occurred while 191 equine cases were reported. The virus is found in birds in many areas of eastern United States but incidence of the disease in people has been confined to the New York City area and northern Florida.

Outbreaks of West Nile disease occurred in Israel in 1951,1954 and 1957, in France in 1962 and South Africa in 1974. For the next 22 years no problems were encountered but in 1996 a serious outbreak occurred in Rumania and this was followed with outbreaks in Italy in 1998 and in Russia and the United States in 1999. Observations in Rumania revealed that few people exposed to the virus developed symptoms. This was confirmed in the United States in 1999 when serological tests conducted for the Center for Disease Control found that only 3-4 percent of the people exposed to West Nile virus became ill. The average age of sick people has been 69, indicating that the disease is of greatest concern to older people.

It is generally accepted that West Nile disease is of relatively minor importance because most people infected with the virus have no symptoms or only experience a mild illness.

FOOT AND MOUTH DISEASE

Foot and mouth disease is a highly contagious viral disease that affects cloven-hoofed animals, such as cattle, sheep, swine and deer. The disease is not a human health hazard but it is of enormous significance in terms of associated social and economic consequences. There has been serious epidemic of foot and mouth disease in Great Britain this year. There were eight outbreaks in the United States between 1870 and 1929 as well as epidemics in Canada in 1952 and in Mexico in 1946 and 1954.

There are seven serologically different viruses associated with the disease. Cloven-hoofed animals may become infected by inhaling or ingesting the virus or by way of damaged skin. The disease develops after a 2 to 14-day incubation period. Affected animals become sick but mortality is low. Symptoms in cattle consist of lesions on the tongue and unusual salivation. Symptoms in sheep are less noticeable and consist of lameness and blisters on the hooves and in the mouth. Infected hog exhibit blisters on hooves, snout and tongue. Swine shed very large amounts of the virus. The foot and mouth virus spreads rapidly among animals on a farm and may be transported to other farms by contaminated people and vehicles or by the movement of infected animals.

Quarantining of farms with diseased animals and the destruction of all susceptible animals on these farms has been the only effective method of controlling foot and mouth disease. These measures inevitably result in enormous financial losses and create social problems because of restrictions imposed on the movement of people and animals. The epidemic in England this year resulted in the mandated destruction of 600,000 cattle, 3,185,000 sheep, 139,000 hogs, 2000 goats, 1000 deer and 200 other animals. This huge disposal problem was achieved by burning the animals. The logistical problems associated with the incinerating large numbers of animals are enormous. The disposal of a single cow by incineration is said to require 50 pounds of wood, 3 bales of hay, 5 tires and the process takes 2 days.

LYME DISEASE

Lyme disease is essentially a disease of white-footed mice as they serve as the principal reservoirs of the spirochete (Borrelia burgdorferi) causing the disease. The disease is very common in the United States along the east and west coasts and the upper mid-west. Over 16,000 cases are reported annually. Old Lyme, Connecticut has the highest incidence (474 cases per 100,000 people) while Kennett Square; Pennsylvania ranks second (397 cases per 100,000 people).

The deer ticks feed on infected white-footed mice through their nymphal stage and become infected with the Lyme disease spirochete. Later the adult ticks feed on deer or sometimes on people and transfer the spirochete to another host. Symptoms of Lyme disease in people consist of a rash around a tick bite followed by flu-like symptoms within a month. The risk of contracting the disease is greatest in or near wooded areas. Most people become infected in their own back yards. Reducing possible exposure to deer ticks is the most practical way to reduce the risk of acquiring the disease. Once the disease is acquired it can usually be successfully treated with antibiotic therapy.

ANTHRAX

Anthrax is a disease affecting all mammals including humans. It is caused by a rod-shaped, spore-forming bacterium (Bacillis anthracis). Death of infected mammals is due to a toxin produced by the bacteria. Antibiotics may eliminate the bacteria from an infected animal but they have no effect on the toxin. The anthrax bacteria have a global distribution and are endemic to the United States. Although all mammals are susceptible there are differences in their recovery rates. Herbivores acquire the bacteria from the soil while carnivores acquire the bacteria by eating contaminated meat or feeds containing contaminated animal byproducts.

Anthrax is present somewhere in the United States almost all the time. The disease is present at this time in North Dakota, Texas, California and Minnesota as well as in two Canadian provinces. Two cases of skin anthrax have been reported this year among Texas ranchers. Hundreds of cattle, horses and deer have died. In cattle the disease most commonly occurs in sexually mature males but it is also found in cows and calves. The disease in humans has declined in the United States since 1943. Cutaneous anthrax has been reported in 98 per cent of the cases while pulmonary and intestinal anthrax made up the balance of the cases.

The bacteria that cause anthrax form spores when exposed to oxygen. Clumps of spores occur attached to soil particles, which makes it especially easy for grazing animals to ingest them. The incubation period in animals is typically 3 to 7 days. Pulmonary anthrax is believed to be rare in animals. Observations in a wool factory in England indicate that humans may inhale 500 to 1000 spores daily without becoming infected. It is supposed that inhalation of 8,000 or more spores are needed to result in pulmonary anthrax.

Control of anthrax in consists of burning the carcasses of infected animals and isolation and vaccination of healthy animals. A vaccine was field tested in humans in 1950 but of its use in people remains controversial because of frequent adverse reactions. The anthrax vaccine is ineffective against the disease in guinea pigs but protects rhesus monkeys against both the cutaneous and inhalation forms of the disease.

LOSSES FROM ANIMAL DISEASES

The animal diseases discussed above (with the exception of foot and mouth disease) are important from the standpoint of human health and also because of associated social and political effects. Many animal diseases have resulted in huge financial losses. Examples are a $63 million loss from avian influenza in the United States in the '80s, a $5 to $7 billion loss from foot and mouth disease in Taiwan, a $9 to $14 billion loss from mad cow disease in England and a $9 billion loss from swine fever recently in the Netherlands. Losses expresses in terms of human health, social or political effects cannot be reliably estimated.

(Summary prepared by S.G. Younkin & J.H. Osborn)

Biographical Sketch

DISCLAIMER
In an effort to provide wide-ranging views and perspectives regarding the practice of and issues surrounding agriculture, the Philadelphia Society for Promoting Agriculture (PSPA) seeks speakers representing a variety of perspectives. The statements and opinions they present are strictly their own and do not necessarily represent the views of PSPA.


	Presentation Summary Animal Diseases and Human Welfare Gary Smith School of Veterinary Medicine University of Pennsylvania Summary Five diseases of wild and domesticated animals have received wide attention in recent years because of their impact on human welfare. These diseases are bovine spongiform encephalopathy, West Nile, foot and mouth, Lyme and anthrax. The diseases and their effects have been summarized below. BOVINE SPONGIFORM ENCEPHALOPATHY Bovine spongiform encephalopathy (BSE or mad cow disease) has been primarily a disease of dairy cattle. It has been responsible for the loss of 180,000 cattle in Great Britain since 1986 with profound economic and political consequences. The disease has occurred less frequently in many European countries but is unknown in the United States. BSE is caused by a prion (an abnormal protein) transmitted in cattle feeds containing contaminated animal byproducts such as meat and bone meal. This prion is believed to cause a disease in humans when contaminated meat is consumed and is similar, but not identical to, Creutzfeldt-Jakob disease (CJD). The variant disease has been designated vCJD to distinguish it from the classical CJD that occurs infrequently but worldwide. The variant vCJD typically affects people less than 52 years of age, while the classical CJD affects people over 63 years old. There have been 107 cases of vCJD in England and the number of cases appears to be increasing each year. This same trend appears to be occurring in European countries. The prion responsible for BSE and vCJD causes proteins in infected cells to spiral in a reverse direction. This reaction renders the proteins insoluble and causes death of the invaded central nervous system cells. BSE is being effectively controlled in England and Europe by prohibiting the use of meat and bone meal in cattle feeds. Because of the long incubation period of the prions, vCJD continues to appear in human populations in England and continental Europe. Prohibiting the importation and use of animal byproducts in cattle feeds has prevented the appearance of BSE in the United States but one case of BSE has been reported in Canada in a cow imported from England. WEST NILE DISEASE West Nile disease is a common disease of birds in Europe, Middle East, Central Asia and Africa caused by a mosquito-borne virus. The virus also attacks horses and people where it causes encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord) that may be fatal. Symptoms in humans vary, but a fever, headache, stiff neck and muscular pains are most common. West Nile virus was first observed in the United States in 1999 when 62 cases and 7 deaths occurred in the vicinity of New York City. In 2000 there were 21 cases and 2 deaths and 60 equine cases diagnosed. In 2001 there were 31 people diagnosed with the virus and 1 death occurred while 191 equine cases were reported. The virus is found in birds in many areas of eastern United States but incidence of the disease in people has been confined to the New York City area and northern Florida. Outbreaks of West Nile disease occurred in Israel in 1951,1954 and 1957, in France in 1962 and South Africa in 1974. For the next 22 years no problems were encountered but in 1996 a serious outbreak occurred in Rumania and this was followed with outbreaks in Italy in 1998 and in Russia and the United States in 1999. Observations in Rumania revealed that few people exposed to the virus developed symptoms. This was confirmed in the United States in 1999 when serological tests conducted for the Center for Disease Control found that only 3-4 percent of the people exposed to West Nile virus became ill. The average age of sick people has been 69, indicating that the disease is of greatest concern to older people. It is generally accepted that West Nile disease is of relatively minor importance because most people infected with the virus have no symptoms or only experience a mild illness. FOOT AND MOUTH DISEASE Foot and mouth disease is a highly contagious viral disease that affects cloven-hoofed animals, such as cattle, sheep, swine and deer. The disease is not a human health hazard but it is of enormous significance in terms of associated social and economic consequences. There has been serious epidemic of foot and mouth disease in Great Britain this year. There were eight outbreaks in the United States between 1870 and 1929 as well as epidemics in Canada in 1952 and in Mexico in 1946 and 1954. There are seven serologically different viruses associated with the disease. Cloven-hoofed animals may become infected by inhaling or ingesting the virus or by way of damaged skin. The disease develops after a 2 to 14-day incubation period. Affected animals become sick but mortality is low. Symptoms in cattle consist of lesions on the tongue and unusual salivation. Symptoms in sheep are less noticeable and consist of lameness and blisters on the hooves and in the mouth. Infected hog exhibit blisters on hooves, snout and tongue. Swine shed very large amounts of the virus. The foot and mouth virus spreads rapidly among animals on a farm and may be transported to other farms by contaminated people and vehicles or by the movement of infected animals. Quarantining of farms with diseased animals and the destruction of all susceptible animals on these farms has been the only effective method of controlling foot and mouth disease. These measures inevitably result in enormous financial losses and create social problems because of restrictions imposed on the movement of people and animals. The epidemic in England this year resulted in the mandated destruction of 600,000 cattle, 3,185,000 sheep, 139,000 hogs, 2000 goats, 1000 deer and 200 other animals. This huge disposal problem was achieved by burning the animals. The logistical problems associated with the incinerating large numbers of animals are enormous. The disposal of a single cow by incineration is said to require 50 pounds of wood, 3 bales of hay, 5 tires and the process takes 2 days. LYME DISEASE Lyme disease is essentially a disease of white-footed mice as they serve as the principal reservoirs of the spirochete (Borrelia burgdorferi) causing the disease. The disease is very common in the United States along the east and west coasts and the upper mid-west. Over 16,000 cases are reported annually. Old Lyme, Connecticut has the highest incidence (474 cases per 100,000 people) while Kennett Square; Pennsylvania ranks second (397 cases per 100,000 people). The deer ticks feed on infected white-footed mice through their nymphal stage and become infected with the Lyme disease spirochete. Later the adult ticks feed on deer or sometimes on people and transfer the spirochete to another host. Symptoms of Lyme disease in people consist of a rash around a tick bite followed by flu-like symptoms within a month. The risk of contracting the disease is greatest in or near wooded areas. Most people become infected in their own back yards. Reducing possible exposure to deer ticks is the most practical way to reduce the risk of acquiring the disease. Once the disease is acquired it can usually be successfully treated with antibiotic therapy. ANTHRAX Anthrax is a disease affecting all mammals including humans. It is caused by a rod-shaped, spore-forming bacterium (Bacillis anthracis). Death of infected mammals is due to a toxin produced by the bacteria. Antibiotics may eliminate the bacteria from an infected animal but they have no effect on the toxin. The anthrax bacteria have a global distribution and are endemic to the United States. Although all mammals are susceptible there are differences in their recovery rates. Herbivores acquire the bacteria from the soil while carnivores acquire the bacteria by eating contaminated meat or feeds containing contaminated animal byproducts. Anthrax is present somewhere in the United States almost all the time. The disease is present at this time in North Dakota, Texas, California and Minnesota as well as in two Canadian provinces. Two cases of skin anthrax have been reported this year among Texas ranchers. Hundreds of cattle, horses and deer have died. In cattle the disease most commonly occurs in sexually mature males but it is also found in cows and calves. The disease in humans has declined in the United States since 1943. Cutaneous anthrax has been reported in 98 per cent of the cases while pulmonary and intestinal anthrax made up the balance of the cases. The bacteria that cause anthrax form spores when exposed to oxygen. Clumps of spores occur attached to soil particles, which makes it especially easy for grazing animals to ingest them. The incubation period in animals is typically 3 to 7 days. Pulmonary anthrax is believed to be rare in animals. Observations in a wool factory in England indicate that humans may inhale 500 to 1000 spores daily without becoming infected. It is supposed that inhalation of 8,000 or more spores are needed to result in pulmonary anthrax. Control of anthrax in consists of burning the carcasses of infected animals and isolation and vaccination of healthy animals. A vaccine was field tested in humans in 1950 but of its use in people remains controversial because of frequent adverse reactions. The anthrax vaccine is ineffective against the disease in guinea pigs but protects rhesus monkeys against both the cutaneous and inhalation forms of the disease. LOSSES FROM ANIMAL DISEASES The animal diseases discussed above (with the exception of foot and mouth disease) are important from the standpoint of human health and also because of associated social and political effects. Many animal diseases have resulted in huge financial losses. Examples are a $63 million loss from avian influenza in the United States in the '80s, a $5 to $7 billion loss from foot and mouth disease in Taiwan, a $9 to $14 billion loss from mad cow disease in England and a $9 billion loss from swine fever recently in the Netherlands. Losses expresses in terms of human health, social or political effects cannot be reliably estimated. (Summary prepared by S.G. Younkin & J.H. Osborn) Biographical Sketch DISCLAIMER In an effort to provide wide-ranging views and perspectives regarding the practice of and issues surrounding agriculture, the Philadelphia Society for Promoting Agriculture (PSPA) seeks speakers representing a variety of perspectives. The statements and opinions they present are strictly their own and do not necessarily represent the views of PSPA.
Home \| Overview \| Program Calendar \| Meeting Abstracts \| Officers and Secretary Listing \| News \| PSPA Library and Archive Send questions and comments to: society@pspaonline.com