foot and mouth disease-

 foot and mouth disease-

 Definition :

foot and mouth disease (sometimes called hoof and mouth disease) is a highly contagious acute disease of all cloven-footed animals caused by aphthovirus characterized by fever and vesicular eruption in the mouth and on the feet .

Etiology :

Picorna virus which is member of the genus aphthovirus.

There are seven serotype of FMD virus : A , O , C , Asia-1 and  southern african territories (SAT) 1 , 2 and 3 .

Picorna virus is non enveloped  , icosahedral  and containing single strained RNA .

Picorna virus is inactivated by temperature above 50 C.

Picorna virus is inactivated by PH lesser than 6.0 or PH more than 9.0 .

Picorna virus is inactivated by NaOH  (2 %) , Na2CO3 (4 %) and the citric acid (.2 %) .

It is sensetive to environmental influence as sunlight and dessication .

It survives for long period at freezing temperature .

Epidemiology :

a)geographical distribution .

Endemic .

Asia , Africa . the middle east , south America and Europe .

Currently , the OIE recognizes countries to be in one of the three diseases states  with regardes to FMD  

1-FMD present with or without vaccination .

2-FMD free with vaccination 

3-FMA  free without vaccination.

b)host range 

Cloven footed domestic (cattle , buffaloes , sheep , goats and swine and somewild animals ).

Other susceptible species , elephants , rats and mice .

Camelidae (camel ) has low susceptibility.

Horses are not susciptable to FMD and humans are rarly affected. 

Morbidity :

100% in susceptible population of domestic animals .

Mortality :

Less than 1% but very high in young animals due to myocarditis.

Sources of virus :

1-Incubating and clinically affected animals .

2-Breathe , saliva  , feces  , urine , milk and semen (up to 4 days before clinical signs ). 

3-Meat and by-products in which PH has remained above 6 .

4-Carriers animals particularly cattle and water buffalo .

5-Recovered cattle may be carrier for 18 to 24 months and recovered sheep may be carrier for 1 - 2 months .

Transmission :

_Direct or indirect contact (mainly by inhalation , ingestion and artificial insemination ).

_Vectors : animate ( humans , pigs , birds ) or inanimate (vehicles ,implement )

_spread over greater distances with movement of infected or contaminated animals , products , objects  and people .

 

Pathogenesis :

Inhalation or ingestion from infected animals and their products.

Replication in the epithelium of the upper respiratory tract or alimentary tract.

Vesicles are formed in 1 -4 days in the lips or oral mucosa .

Followed by viremia and pyrexia .

Secondary vesicles are formed 2 days later .

Hydropic degeneration (balloon degeneration ) followed by necrosis .

In young animals , the virus tends to localize in the myocardium (known as tiger heart ) leading to sudden death .

NB grayish or yellowish streaking in the myocardium (degeneration and necrosis ) in heart of young animal  and called tiger heart .

Incubation period 2 to 21 days ( average 3-8 days )

Clinical finding :

_Fever ( 103 to 105 F )

_Dullness.

_Anorexia 

_Shivering

_Reduction in milk production for 2 - 3 days.

_Blisters on buccal and nasal mucosal membrane including mouth , tongue and lips .

_Blisters between claws and coronary band and evenon the udder and teat .

_After 24 hours , rupture vesicle leaving erosion .

_sticky , foamy , stringy saliva drips from the mouth of animal.

_Painful tongue and mouth that decrease in  appetites ,resulting in loss weight .

Signs in sheep and goats

_Lesions are less pronounced .

_Foot lesions may go unrecognized.

_Lesions in dental pad of sheep.

_Agalactia

Signs in pig 

_ Lesions are observed in snout.

_ Sever foot lesions particularly when it is housed on concrete .

_ High mortality in piglets .

Sequelae to FMD in cattle 

_ Tongue erosions .

_ Hoof deformation .

_ Mastitis .

_ Breeding problems .

_ Secondary infection .

_ Abortion .

_ Low milk production .

_ Myocarditis and death in young .

_ Diabetes mellitus .

_Panting 

_Pituitary gland damage .

 

Diagnosis 

 _ case history .

_ clinical signs .

_ collection samples / specimens ( oral , nasal , foot or   mammary  lesions  are good sources of specimens , vesicular fluid , epithelium covering a vesicle (.5 gm ) , about 5 ml blood with anticoagulant , esophageal - pharyngeal fluid .

_ isolation and identification .

10 % suspension preparation .

Inoculation into susceptible tissue culture ( primary bovine thyroid  cells and primary pig, calf and lamb kidney cells  ,inoculation of  BHL-21 and IB-RS-2 cell lines )

_ CFT , ELISA  and RT PCR .

Differential diagnosis 

1- FMD : vesicle , myocarditis and  gastroentritis .

2- VE ( vesicular exanthema ) : vesicle but no myocarditis and gastroenteritis .

3-VS (vesicular stomatitis ) :  less conspicuous vesicles , no myocarditis and gastrointeritis .

Treatment 

_Washing affected area with mild disinfectant ( 2% caustic soda , 4% soda ash ,and 2% acetic acid )

_ Applying antibiotics locally .

_ protective dressing to inflamed area to prevent secondary infection .

_Sulfadimidine or broad-spectrum antibiotics injections are useful to the secondary bacterial infection .

_ A good systemic response is reported to the administration of  flunixin meglumine .

_ Fly repellent must be used.