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Animal Infectious Diseases

Avian Influenza in the United States

A Threat to U.S. Poultry

Worldwide, there are many strains of avian influenza (AI) virus that can cause varying amounts of clinical illness in poultry. AI viruses can infect chickens, turkeys, pheasants, quail, ducks, geese, and guinea fowl, as well as a wide variety of other birds. Migratory waterfowl have proved to be the natural reservoir for this disease.

AI viruses can be classified into low pathogenic (LPAI) and highly pathogenic (HPAI) forms based on the severity of the illness they cause. Most AI virus strains are LPAI and typically cause little or no clinical signs in infected birds. However, some LPAI virus strains are capable of mutating under field conditions into HPAI viruses.

HPAI is an extremely infectious and fatal form of the disease for chickens. The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) works to keep HPAI from becoming established in the U.S. poultry population. HPAI can strike poultry quickly without any infection warning signs. Once established, the disease can spread rapidly from flock to flock. It is essential for the U.S. poultry industry to be alert to this disease threat.

Clinical Signs

Birds affected with HPAI may show one or more of the following signs:

  • Sudden death without clinical signs
  • Lack of energy and appetite
  • Decreased egg production
  • Soft-shelled or misshapen eggs
  • Swelling of the head, eyelids, comb, wattles, and hocks
  • Purple discoloration of the wattles, combs, and legs
  • Nasal discharge
  • Coughing, sneezing
  • Incoordination
  • Diarrhea

Potential Threat to Human Health

In some instances, strains of HPAI viruses can be infectious to people. Human infections with the avian influenza viruses under natural conditions have been documented in recent years. The H5N1 strain, isolated in Hong Kong in 1997, was highly pathogenic for chickens and caused a limited outbreak in 18 people. Six of these individuals died. Since mid-December 2003, a growing number of Asian countries have reported outbreaks of HPAI in chickens and ducks. The rapid spread of HPAI, with outbreaks occurring at the same time, is historically unprecedented and of growing concern for human health as well as for animal health.

Source: Animal & Plant Health Inspection Service. For more details see link below.

Special Note: For new Avian Influenza (Bird Flu) information, click here.

Bovine Spongiform Encephalopathy (BSE)


Bovine spongiform encephalopathy (BSE), widely known as "mad cow disease," is a chronic, degenerative disease affecting the central nervous system of cattle. Worldwide there have been more than 180,000 cases since the disease was first diagnosed in 1986 in Great Britain. BSE has had a substantial impact on the livestock industry in the United Kingdom. The disease has also been confirmed in native-born cattle in Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Ireland, Israel, Italy, Japan, Luxembourg, Liechtenstein, the Netherlands, Northern Ireland, Poland, Portugal, Slovakia, Slovenia, Spain and Switzerland. However, over 95% of all BSE cases have occurred in the United Kingdom. BSE is not known to exist in the United States.

BSE belongs to the family of diseases known as the transmissible spongiform encephalopathies (TSE's). These diseases are caused by a transmissible agent which is yet to be fully characterized. They share the following common characteristics:

  1. a prolonged incubation period of months or years;
  2. a progressive debilitating neurological illness which is always fatal;
  3. when examined by electron microscopy, detergent treated extracts of brain tissue from animals or humans affected by these diseases reveal the presence of scrapie associated fibrils (SAF);
  4. pathological changes appear to be confined to the CNS and include vacuolation, and astrocytosis;
  5. the transmissible agent elicits no detectable specific immune response in the host which has inhibited the development of a preclinical live animal diagnostic test to date.

Clinical Signs of BSE in Cattle

Affected animals may display changes in temperament, such as nervousness or aggression; abnormal posture; incoordination and difficulty in rising; decreased milk production; or loss of body condition despite continued appetite. There is no treatment, and affected cattle die.

The incubation period ranges from 2 to 8 years. Following the onset of clinical signs, the animal's condition deteriorates until it dies or is destroyed. This usually takes from 2 weeks to 6 months. Most cases in Great Britain have occurred in dairy cows between 3 and 6 years of age.

Can the USDA guarantee that BSE will never occur in the United States?

There are still a number of unknowns regarding the origin and transmission of BSE. Given these scientific uncertainties, we cannot assure zero risk from BSE. However, we can and will continue to monitor new scientific findings and world events and adjust our regulations and policies to keep the risk of BSE infecting the national herd as low as possible.

One BSE Case Has Been Found in the United States

One case of BSE has been confirmed in the U.S.A. with 13 years of active surveillance. On December 23, 2003 a dairy cow in Washington State was diagnosed with BSE. The cow originated in Canada. USDA has changed slaughter rules and increased testing for BSE. Any suspected animal is with held from the food and feed supply until testing confirms it free of BSE.

Source: Animal & Plant Health Inspection Service. For more details see link below.

Foot-and-Mouth Disease (FMD)

Foot-and-mouth disease (FMD) is a severe, highly communicable viral disease of cattle and swine. It also affects sheep, goats, deer, and other cloven-hooved ruminants. FMD is not recognized as a zoonotic disease.

This country has been free of FMD since 1929, when the last of nine U.S. outbreaks was eradicated. The disease is characterized by fever and blister-like lesions followed by erosions on the tongue and lips, in the mouth, on the teats, and between the hooves. Many affected animals recover, but the disease leaves them debilitated. It causes severe losses in the production of meat and milk. Because it spreads widely and rapidly and because it has grave economic as well as clinical consequences, FMD is one of the animal diseases that livestock owners dread most.

What Causes It

The disease is caused by a virus. The virus survives in lymph nodes and bone marrow at neutral pH, but destroyed in muscle when in pH<6.0 i.e. after rigor mortis. The virus can persist in contaminated fodder and the environment for up to 1 month, depending on the temperature and pH conditions. There are at least seven separate types and many subtypes of the FMD virus. Immunity to one type does not protect an animal against other types.

How It Spreads

FMD viruses can be spread by animals, people, or materials that bring the virus into physical contact with susceptible animals. An outbreak can occur when: * People wearing contaminated clothes or footwear or using contaminated equipment pass the virus to susceptible animals.

  • Animals carrying the virus are introduced into susceptible herds
  • Contaminated facilities are used to hold susceptible animals.
  • Contaminated vehicles are used to move susceptible animals.
  • Raw or improperly cooked garbage containing infected meat or animal products is fed to susceptible animals.
  • Susceptible animals are exposed to materials such as hay, feedstuffs, hides, or biologics contaminated with the virus.
  • Susceptible animals drink common source contaminated water.

Source: Animal & Plant Health Inspection Service. For more details see link below.

New Mexico Livestock Board Web Site

The New Mexico Livestock Board was created in 1887 by the Territorial Legislature to combat the spread of contagious Animal Diseases originating from Texas (Texas fever) and to prevent the theft of livestock. This agency has continued to maintain its relevance over its 117 year history meeting the changing needs of agriculture in New Mexico.

Special Note: For new Avian Influenza (Bird Flu) information, click here.

Vesicular Stomatitis (VS)

Vesicular Stomatitis (VS), a domestic viral disease that primarily affects horses, cattle and swine, has appeared early this year. Laboratory tests completed April 27 confirmed the infection in two horses on a premises in Grant County, in southwest New Mexico. VS appears sporadically, usually involving New Mexico, Texas, Arizona, Colorado and occasionally, other states. Recent outbreaks occurred in 1995, 1997, 1998 and 2004, with initial cases detected in mid-May or early June. Outbreaks usually end in early winter. VS outbreaks cause concern among ranchers, because signs mimic those of foot-and-mouth disease (FMD), a highly contagious and dangerous foreign animal disease. VS can cause production losses, because affected livestock may develop blister-like lesions and open sores in the mouth, dental pad, tongue, lips, nostrils, hooves and teats. During the usual two- to three-week healing time, infected animals may be lame, or refuse to eat or drink. Dams may reject their nursing offspring, and dairy cattle can experience a severe drop in milk production.

"VS-infected animals, and all other susceptible livestock on a premises are quarantined until 30 days after all lesions are healed," said Dr. Dee Ellis, who heads up field operations for the Texas Animal Health Commission (TAHC), the state's livestock and poultry health regulatory agency. "This ensures that sick animals are not moved, and helps prevent the disease from being spread by direct contact or through contaminated saliva or drainage from sores. Prior to quarantine release, animals are re-examined by a state or federal regulatory veterinarian."

Dr. Ellis noted that some states place prohibitions or restrictions on livestock moved from VS-affected states. TAHC regulations require livestock from affected states to be accompanied by a valid certificate of veterinary inspection (health paper) on which the accredited veterinarian certifies the animals are not from a quarantined premises.

"We urge livestock owners in Texas to report any signs of VS to their private veterinary practitioner or the TAHC," commented Dr. Ellis. "History could repeat itself. In 2004, Texas had confirmed cases on 15 premises. In Colorado, VS was detected on 199 ranches, and on 80 sites in New Mexico."

"A free laboratory test will ensure the animal's blisters or sores are from VS and not from an introduction of foot-and-mouth disease into the U.S," urged Dr. Ellis. "If you examine sick animals, wear latex or rubber gloves and practice good hygiene, as VS can be contagious to humans, resulting in short-term flu-like symptoms."

To report suspected cases of VS, owners and private veterinary practitioners should call their respective state's livestock health regulatory agency:

  • Texas Animal Health Commission - 1-800-550-8242 (operational 24 hours a day)
  • New Mexico Livestock Board - 1-505-841-6161
  • Colorado Department of Agriculture, State Veterinarians Office - 1-303-239-4161