Monday, June 11, 2001

Infectious Diseases

Infectious Diseases that Threaten the United States Beef Industry

Infectious Disease is defined as any disease caused by the entrance, growth and multiplication of bacteria, protozoon’s or viruses in the body. An infectious disease may or may not be contagious.
Contagious Disease is defined as a type of infectious disease caused by receiving living germs directly from an affected animal with the disease or by contact with a secretion or some object previously contaminated.
Many infectious diseases are not contagious, but some special method of spreading or inoculation of the germs is required.

Foot-and-Mouth Disease (FMD) is one of the most dreaded infectious diseases in the world and difficult to control. It is caused by a highly contagious aphthovirus of the family Picornaviridae and has no cure. It infects cattle but also pigs, sheep, goats, buffalo and artiodactyl wildlife species- animals with cloven hooves. FMD is characterized by fever, vesicles in the mouth and on the muzzle, teats, and feet; eventhough the mortality is low, it can cause death in young animals.

There are seven immunologically distinct types: A, O, C, Asia 1, and SAT (Southern African Territories) 1, 2, and 3. Within each serotype there is a large number of strains that exhibit a spectrum of antigenic characteristics; therefore, a number of vaccine strains for each serotype, particularly O and A, are required to cover antigenic diversity.

Transmission of FMD is generally by contact between susceptible and infected animals. Infected animals have a large amount of aerosol virus in their exhaled air, which can infect other animals via the respiratory or oral routes. All excretions and secretions from infected animal contain virus and have a remarkable capacity for remaining viable in carcassses, animal by-products, water, straw bedding and even in pastures. It is spread by direct contact, ingestion or inhalation. The virus can survive in dry fecal material for 14 days in summer, in slurry up to 6 months in winter, in urine for 39 days and on soil between 3 and 28 days.

Ruminants that have recovered from infection and vaccinated ruminants that have contact with live FMD virus can remain infected and carry the virus in the pharyngeal region for up to 2.5 years in cattle, 9 months in sheep and possibly lifelong in the African buffalo.

The primary site of infection and replication is usually the mucosa of the respiratory tract, although the virus can enter through skin abrasions or the GI tract. Replication then occurs in the local lymph node, and infection spreads via the blood stream to predilection sites in the epithelium of the mouth, muzzle, feet, and teats, and also to areas of damaged skin. Vessicles develop at these sites and rupture, usually within 48 hours. The viremia persists for at least 5 days.

The incubation period for FMD is two to fourteen days, depending upon the infecting dose, susceptibility of the host and strain of the virus. After the incubation period, a fever of up to 106°F (41°C) develops, the animal is anorectic and salivates and stamps its feet as vesicles develop on the tongue, dental pad, gums, lips, and on the coronary band and interdigital cleft of the feet. Vesicles may also develop on the teats and udder, particularly of lacting cows and sows, and on areas of skin subject to pressure and trauma, such as legs of pigs. Young calves; lambs, kids, and piglets may die before showing any vesicles because of virus-induced damage to the developing cells of the myocardium. Vesicles in the mouth, even when severe, usually heal within seven days, although recovery of the tongue papillae takes longer. Lesions on the mammary gland and feet frequently develop secondary infections, resulting in mastitis, underrunning of the sole and chronic lameness. In pigs, the complete horn of the toe may be lost. Cattle and deer may also lose one or both horns of the foot.

In cattle and pigs, the clinical signs of FMD are indistinguishable from those of vesicular stomatitis and vesicular exanthema.

Mortality is low, but the economic losses are catastrophic because of the strict quarantine and eradication programs. United States has a policy of slaughtering of all affected and in-contact susceptible animals and strict restrictions on movement of animals and vehicles around infected premises. After slaughter, the carcasses are either burned or buried on or close to the premises, and the buildings are thoroughly washed and disinfected with mild acid or alkali and by fumigation. Because of the sensitivity of the virus to acid and alkaline pH, sodium hydroxide, sodium carbonate, and citric or acetic acid are effective disinfectants.

  Control is by movement restriction, quarantine of affected premises, and vaccination (last option) around the affected premises. FMD vaccine is a killed preparation and at best, affords good protection against challenge for four to six months. The antigenic diversity of strains of FMD virus within each of the serotypes is an additional complication, so it is necessary to ensure that vaccines contain strains antigenically similar to the potential outbreak strains.

Anthrax is an acute, serious infectious febrile disease of virtually all warm-blooded animals, including man and occurs naturally in animals in South Dakota, Nebraska, Arkansas, Mississippi, Louisiana, Texas, and California.

Anthrax is a disease caused by a spore-forming bacteria called Bacillus anthrasis and after the bacilli have been discharged from an infected animal or exposed to oxygen from an opened carcass, they form spores that are resistant to extremes of temperature, chemical disinfectants, and desiccation. For this reason, the carcass of an animal dead from suspected anthrax should not be necropsied.

Bacillus produces an edema toxin and a lethal toxin. Both toxins, gain entry to target cells by competitive binding with a third protein, protective antigen, that has a membrane translocation function. The toxins and the capsule are the primary virulence factors of the anthrax bacillus.

Outbreaks of anthrax commonly are associated with neutral or alkaline, calcareous soils that serve as incubator areas for the organisms. In these areas, the spores apparently revert to the vegetative form and multiply to infectious levels when environmental conditions of soil, moisture, temperature, and nutrition are optimal. Cattle, horses, sheep, and goats may readily become infected when grazing such areas.

During an epidemic, flies and other biting insects may mechanically transmit the disease from one animal to another, but this mode of transmission is of minor importance. Infection also may be caused by consumption of contaminated feedstuffs, eg, meat and bone meal. Occasionally, crops such as hay grown on contaminated soil have caused small outbreaks. Pigs, dogs, cats, mink, and wild animals in captivity have acquired the disease from consumption of contaminated meat.

The incubation period is three to seven days and the clinical course of the disease ranges from peracute to chronic. The peracute form is characterized by sudden onset and a rapidly fatal course. Staggering, dyspnea, trembling, collapse, a few convulsive movements, and death may occur in cattle, sheep, or goats without any previous evidence of illness.

In acute anthrax of cattle and sheep, there is an abrupt rise in body temperature and a period of excitement followed by depression, stupor, respiratory or cardiac distress, staggering, convulsions, and death. There may be bloody discharges from the natural body openings.

Chronic infections are characterized by localized, subcutaneous, edematous swelling that can be quite extensive. Areas most frequently involved are the ventral neck, thorax, and shoulders.

Rigor mortis is frequently absent or incomplete. Dark blood may ooze from the mouth, nostrils, and anus with marked bloating and rapid body decomposition. The blood is dark and thickened and fails to clot readily. If the carcass is inadvertently opened, septicemia lesions are seen. Hemorrhages of various sizes are common on the serosal surfaces of the abdomen and thorax as well as on the epicardium and endocardium. An enlarged, dark red or black, soft, semifluid spleen is common. The liver, kidneys, lymph nodes usually are congested and enlarged.

Anthrax must be differentiated from other conditions that cause sudden death. In cattle and sheep, clostridial infections, bloat, and lightning strike may be confused with anthrax.
A confirmatory laboratory examination should be done by collecting a small amount of blood from a superficial vessel such as the jugular vein. Before submission, the laboratory should be contacted to determine appropriate shipping procedures.

Anthrax in livestock can be controlled by annual vaccination of all grazing animals in the endemic area and by implementation of control measures during outbreaks. Vaccination should be done two to four weeks before the season when outbreaks may be expected.

Specific control procedures are necessary to contain the disease and prevent its spread. These include:
     1. Notification of the appropriate regulatory officials and your veterinarian;
     2. Rigid enforcement of quarantine;
     3. Prompt disposal of dead animals, manure, bedding, or other contaminated material
         by cremation or deep burial;
     4. Isolation of sick animals and removal of well animals from the contaminated area;
     5. Disinfecting of stables, pens, milking barns, and equipment used on livestock;
     6. Use of insect repellents;
     7. Control of scavengers that feed on animals dead from the disease;
     8. Observation of general sanitary procedures by people who contact diseased animals.

Anthrax in humans is rare. Most cases develop in people whose occupation place them in close contact with livestock or the contaminated products of livestock such as wool, goatskin, and pelts. Direct human-to-human transmission of anthrax is extremely unlikely, and most experts question whether it is possible.

Three types of anthrax are seen in people: cutaneous (skin), intestinal, and inhalation. The incubation for the disease is approximately two to seven days.

In people, cutaneous anthrax accounts for about 95% of all natural infections and develops when the anthracis bacteria enter the skin through cuts or abrasions. Without antibiotic therapy, the death rate from cutaneous anthrax is approximately 20%; if appropriately treated, death is rare.

Intestinal anthrax results from consumption of contaminated and undercooked meat. Affected individuals may experience nausea, inappetence, vomiting, and fever, followed by abdominal pain, blood in the vomitus, and severe diarrhea. Mortality is estimated at 25-75%. Human intestinal anthrax has not been reported in the United States during the 20th and 21st centuries.

Inhalation anthrax may initially present as a flu-like illness. A short period of improvement may follow, after which the patient rapidly deteriorates with high fever, respiratory distress, and shock. Fatalities approach 95% if not treated within the first 48 hours.

Infection can be prevented and treated with antibiotics. Because the course of the disease is rapid, prompt administration is essential. Effective antibiotics include ciprofloxacin, doxycycline, and amoxicillin. Vaccination is effective at preventing infection in animals and people. Animal vaccines have not been approved for and should not be administered to humans. A vaccine is available for humans, but population-wide vaccination in the United States has not been recommended because risk has been considered low.

Vesicular Stomatitis (VS) is a viral disease of cattle, swine, and horses and characterized clinically by the development of vesicles of the mouth, feet, and teats. On occasion this infection occurs in man as an influenza-like disease. This sporadic, re-emerging viral disease is endemic in the warmer regions of the Western Hemisphere and in the United States it’s mostly in the Southwest.

Aside from its negative economic impact on livestock, VS is significant because of its outward signs are similar to foot-and mouth disease (FMD).

Vesicular Stomatitis is caused by two distinct rhabdoviruses designated as the New Jersey and Indiana types. The New Jersey type is the most common isolated. How VS spreads is not fully known; insect vectors, mechanical transmission and movement of animals may be responsible. Once introduced into the herd, the disease moves from animal to animal by contact or exposure to saliva or fluid from ruptured blisters.

Clinical signs include vesicular lesions on the tongue, oral mucosa, teats or coronary bands of the feet, fever, drooling or frothing at the mouth. Oral lesions can be so painful that animals refuse to eat or drink resulting in severe weight loss. Foot lesions can also result in lameness.

The only way to diagnose and differentiate VS from FMD is through laboratory tests. Suspected cases should immediately brought to the attention of state or federal authorities.

No control measures are taken eventhough there is a vaccine available in some countries of the American tropics. Since it is a self-limiting, non-fatal viral disease, treatment is also not usually undertaken. The systemic effects of the viral infection are non-responsive to therapy and the local lesions in the mouth or on the feet or udder also usually heal without any therapeutic intervention. Maintaining the affected animals in a hygienic environment is recommended to prevent secondary bacterial infection.


The Merck Veterinary Manual, Eighth Edition, CD-ROMÓ2000, Merck & Co., Inc.
Generalized Conditions; Foot and Mouth Disease; Anthrax; Vesicular Stomatitis;

Texas Animal Health Commission:

National Cattlemen’s Beef Association:

American Veterinary Medical Association
Anthrax Fact Sheet 10/12-2001

Texas Cooperative Extension Service, The Texas A & M University System, College Station, Texas. Official Dept. of Defense web site for Anthrax

Centers for Disease Control