Foot and Mouth Disease (FMD) (Aphthous Fever)
It is a highly contagious viral disease of all cloven-footed animals characterized by fever, ropy salivation, and vesicular eruptions on the buccal mucosa, the skin of interdigital space, coronary band, and teat.
Cause of FMD
It is an RNA Apthovirus of the family Picornaviridae.
Seven major serotypes are known namely A, O, C, South African SATI, SAT2, SAT3, and Asial, serotypes about 80 sub-serotypes were identified.
There is no cross-protection between serotypes and sub-serotypes within the same strain.
It undergoes antigenic drift, leading to new subtypes.
It is present in secretions and excretions before the development of clinical signs for a short period.
Resistance of FMD virus.
The virus remains alive in frozen meat for up to 80 days and may persist for a year in infected premises and 3 months in feed.
Also, This virus is pH sensitive, it is destroyed by sodium hydroxide 2%, sodium carbonate 4% and acetic acid 5%, formalin 1 - 2%, boiling, and sunlight.
Distribution of the disease
It is worldwide distributed and enzootic in Egypt.
What are the animals susceptible to FMD?
All cloven-footed domestic and wild animals are susceptible.
Cattle and buffaloes are the most susceptible animals, followed by pigs.
African and Indian buffaloes may develop in apparent persistent infection.
Sheep, goats, and wild animals such as deer, antelope, and elephant are susceptible.
Camels may be infected.
The zoonotic importance of FMD
Peoples handling infected animals become carriers and have the virus in their nasopharynx for 24 hours.
Children are infected through the drinking of infected milk.
Sources of FMD infection:
There are many sources of FMD infection, including:
Carrier or latently infected animals.
Sheep, goats, and cattle remain as carriers after recovery up to 6 months due to continuous multiplication of the virus in pharyngeal tissues and mammary glands.
Meat and meat products, especially bone marrow and semen.
Contaminated bedding, feed, water, and milk
Reservoirs as rodents, birds, and wild ruminants,
How can FMD be transmitted?
Infection occurs through:
Ingestion of infected material.
Inhalation of infected droplets.
The disease is rapidly transmitted as air-born or wind-born for up to 100 km.
Mechanical transmission through migrating birds, dogs, cats, rodents, wild animals, ticks, and man.
Pathogenesis of FMD in cattle
After infection, the virus gains access to regional lymph nodes and then reaches the blood resulting in transitory viremia for 4-6 days.
Multiplication and localization of the virus in the predilections tissues such as:
The epithelium of the mouth, pharynx, esophagus, and stomach.
Feet and teats.
The cardiac muscle of the calves.
Vesicles are formed then rupture with ulcer formation at these sites due to continuous irritation by the virus and degenerative changes of the epithelium.
Myocarditis and necrosis of the heart muscle occur in calves. Incubation period: 3-8 days.
Clinical signs of FMD in cattle
FMD in cattle has many clinical signs, including:
Fever for 1-4 days, with a rapid fall in milk yield.
Vesicles are 1-2 cm in diameter thin-walled and contain straw-colored fluid that appears on the oral mucosa, especially the dental pad and tongue.
The vesicles rupture within 24 hours, leaving ulcers that heal in 1-2 weeks.
Fever subsides when the vesicles rupture.
Ropy salivation with a characteristic smacking sound.
Vesicles appear on interdigital space and coronary bands of the feet, rupture of these lesions causes lameness.
Other vesicles also develop on the teat orifices and act as a predisposing factor for mastitis.
Myocardial and skeletal muscle necrosis occurs in young calves up to 9 months before the appearance of the characteristic signs.
Some surviving calves may develop severe dyspnea during exercise (panters).
Complications and risk factors of FMD in cattle
The risk factors of FMD in cattle include:
Morbidity rate:
It may reach up to 100%.
In enzootic areas: Animals may have partial immunity and the disease may be mild or subclinical.
Mortality rate:
It exceeds 5%
In calves, it may reach up to 50-70% and suckling calves up to 100%.
Abortion.
Drop-in milk yield.
Mastitis due to secondary infection.
Hoof separation.
Myocardial degeneration.
Endocrine damage leads to a lack of heat tolerance, dyspnea, diabetes mellitus, and overgrowth of hair.
The examination of the dead carcass shows:
Vesicles, erosions or ulceration in the oral cavity, pharynx, esophagus, rumen pillars, trachea, bronchi, and skin of the foot and teats.
Necrosis and degeneration of the heart muscle fibers in calves give a striped appearance (tiger heart).
Diagnosis of FMD in cattle
The disease can be diagnosed through:
Clinical signs and lesions.
Laboratory diagnosis which includes:
Isolation of the virus from Vesicular fluid, epithelial tissue from edges of ruptured vesicles, and blood from viremic cases.
Identification of the virus by VNT, FAT, or PCR.
Animal inoculation through:
Intraperitoneal injection of unweaned mice with the suspected materials results in paralysis of hind limbs and death within a week.
Intradermal injection of fresh vesicular fluid into the footpads of Guinea pigs vesicles appears on all pads in 1-7 days and secondary vesicles in the month 1-2 days.
Differential diagnosis:
FMD should be differentiated from:
Diseases with vesicular lesions such as:
Vesicular stomatitis
Bluetongue disease.
Mucosal diseases such as:
Rinderpest.
Bovine viral diarrhea.
Infectious bovine rhinotracheitis.
Malignant catarrhal fever.
Diseases causing lameness, such as:
Footrot.
Other diseases such as:
Bovine papular stomatitis.
Bovine herpes mammilitis.
Pox.
The control of FMD in cattle depends mainly on:
Symptomatic treatment:
Use drugs to overcome the clinical signs, such as:
Antipyretics, analgesics, and anti-inflammatory such as Phenylbutazone 2.5 ml/ 100kg bodyweight, i/v or i/m for three to five days, or Phenylbutazone and acetyl-salicylic acid 10 ml/ 100 kg body weight, i/v or i/m for three to five days).
The use of antibiotics to overcome the secondary bacterial infection, including Tetracycline and Chloramphenicol.
Washing of the mouth with an antiseptic solution such as Potassium Permanganate 1/1000, Boric acid 1-2%, and Sodium bicarbonate 5%.
Vitamin A therapy to enhance the resistance of the oral mucosa by using oral dosing of cod liver, Vitamin AD3, E, or Multivitamins.
Wash the foot lesions with 5% copper sulfate then use antibiotic ointment or medical tar which acts as a repellent, insulator, and antiseptic.
Fluid therapy.
Hygienic Measures:
Vaccination is the major key for disease control
so, Vaccination against FMD using one of the different types of FMD vaccines is necessary.
In free areas:
Prohibition of importation of animals or animal products such as meat, milk, semen, hormones, and vaccines from infected areas.
Animals should be kept in quarantine for 21 days.
Epizootic in the free area:
Stamping out of all infected cloven-footed animals.
Restriction of animal movement.
Disinfection of the farm using 1-2% sodium hydroxide or formalin.
Farms should be left unstocked for 6 months.
Vaccination using the inactivated vaccine as ring vaccination around the infected focus.
Enzootic areas:
The hygienic measures are recommended during an outbreak including:
Notification and quarantine of infected areas.
Restriction of animal movement.
Closing of markets.
Hygienic disposal of dead carcasses.
Regular detection and elimination of carriers.
Infected bulls should not be used for natural insemination services or artificial insemination.
Milk from infected animals should not be used for calves or humans.
Finally, FMD is one of the most serious and economical dangers of high risks for cattle.
Written by: Dr. Mai Foda
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