World veterinarian Quiz - 37

 

Bovine Virus Diarrhoea / Mucosal Disease

ü BVD /MD is a viral disease of young cattle (6–24 month old) associated with various clinical presentation can range from inapparent or subclinical infection to acute and severe enteric disease to the highly fatal mucosal disease complex which is characterized by profuse enteritis in association with typical mucosal lesions.

ü  BVD /MD is  OIE-Listed disease

Etiology

•      Bovine viral diarrhoea virus (BVDV) :-   RNA virus

•      Highly mutable virus

•      Many strains; Pathogenicity differences

•      tissue tropism differences

•      Genotype – Type I and II

•      Biotypes

1.    NCP (Noncytopathic / wild)

2.    CP (Cytopathic /mutant)

•      Genus:  Pestivirus

•      Family: Flaviviridae

•      BVDV is closely related to ovine Border disease viruses and

classical swine fever

 Host

•      Primarily a disease of domestic cattle

•      Can infect most even-toed ungulates :-  e.g. goats, sheep, water buffaloes, pig, camelids

Transmission

•      Direct contact 

•      All secretion and excretion of persistently infected animals

•      Aborted fetus

•      Infected bull semen

•      In utero infection

•      Contaminated food, water, fomites

Pathogenesis

1. BVDV (Noncytopathic / wild)  infection to immunocompetent, seronegative, nonpregnant animals → Bovine viral diarrhea (BVD)
2. BVDV (Noncytopathic / wild) infection to immunocompetent, seronegative, pregnant animals → Either Abortion or Persistent Infection
3. Persistently infected calves with NCP-BVDV → Infected with CP (Cytopathic /mutant)virus → Development of Mucosal disease  

 

 

A.   BVDV (Noncytopathic / wild)  infection to immunocompetent, seronegative, nonpregnant animals → Bovine viral diarrhea (BVD)

 

NCP virus enter in to body of Immunocompetence nonpregnant cattle (6 to 24 months) 

⇓

Virus reach to the tonsils 

⇓

virus infect lymphocytes, monocytes and dendritic cells  

⇓

Virus replication in this cells 

⇓

infect other lymphocytes, monocytes, macrophages 

⇓

Infected cells enter in to blood circulation via thoracic ducts 

⇓

disseminated to all visceral organs via blood 

⇓

Reach to the lymphoid tissues and the subepithelial connective tissue of the dermis and GI tract 

⇓

spreads locally to overlying epithelial cells 

⇓

Induced necrosis of lymphoid cells and overlying mucosa 

⇓

Erosions, ulcers and diarrhea (due to loss of enterocyte )

•       Sometime NCP – BVDV (Genotype II) affect megakaryocytes of bone marrow → Decreased  production of platelets →Thrombocytopenia →  Generalized hemorrhages

B.   BVDV (Noncytopathic / wild) infection to immunocompetent, seronegative, pregnant animals → Either Abortion or Persistent Infection

 

NCP virus enter in to body of Immunocompetence pregnant cattle 

⇓

Virus reach to the tonsils 

⇓

virus infect lymphocytes, monocytes and dendritic cells  

⇓

Virus replication in this cells 

⇓

infect other lymphocytes, monocytes, macrophages 

⇓

Infected cells enter in to blood circulation via thoracic ducts 

⇓

disseminated to all visceral organs via blood 

⇓

Reach to the caruncular side of placentomas 

⇓

Infect tropoblast 

⇓

Virus replication 

⇓

cross placenta 

⇓

Reach to the fetal circulation 

⇓

infect macrophage like cells 

⇓

Fetal infection

Abortion

•      50-100 days of gestation period observed Fetal death, abortion, mummification

•      100-150 days of gestation: Congenital defects

Fetus survive 

·         Infection occur around 135 days of gestation period: - Virus consider as part of fetal tissue → failure of the immature fetal immune system to recognize the infecting viral antigens as "not-self" or foreign. Persistent infection 

 

C.   Persistently infected calves with NCP-BVDV → Infected with CP (Cytopathic /mutant) virus → Development of Mucosal disease  

 

NCP virus in persistently infected calves 

⇓

Mutation 

⇓

Converted to CP virus / CP virus from other infected animal (NCP and CP virus act synergistically ) 

⇓

Virus reach to the tonsils

⇓

virus infect lymphocytes, monocytes and dendritic cells 

⇓

Virus replication in this cells

⇓

infect other lymphocytes, monocytes, macrophages

⇓

Infected cells enter in to blood circulation via thoracic ducts

⇓

disseminated to all visceral organs via blood

⇓

Enter in to the MALT of GIT and oral mucosa

⇓

Infect dendritic cells and B lymphocytes

⇓

death of overlying mucosa of intestine, oral cavity and lymphocytes

⇓

Diarrhea, oral ulceration and leukopenia →

⇓

Immunosuppression

⇓

Death

Clinical Signs: BVD

•      Fever

•      Leukopenia

•      Lethargy

•      Anorexia

•      Mild oculonasal discharge

•      Diarrhea – May contained blood

•      Thrombocytopenic syndrome – Generalized hemorrhages

•      In severe acute diseases - sudden death, diarrhea, or pneumonia 

Peracute form of Bovine Viral Diarrhoea:-

          ·         Fever up to 42.0°C

          ·         Agalactia in adult lactating cows are commonly observed.

          ·         Severe depression

          ·         Respiratory distress

          ·         Anorexia

          ·         Profuse watery diarrhea

          ·         Dysentery,

          ·         Conjunctivitis

          ·         Peracute form of the enteric form of the disease animals infected with highly virulent                BVDV-2 strains

          ·         Thrombocytopenia in young and adult immunocompetent animals also infected with                highly virulent BVDV-2.

          ·         Thrombocytopenia and Haemorrhagic Syndrome

          ·         Platelet counts:- below 25,000 cells/μL

          ·         NCP only cause Thrombocytopenia not CP

          ·         15 month old heifer calf reported neurological sign and multifocal Meningoencephalitis            by highly virulent BVDV-2

         ·        BVDV has been incriminated in bovine respiratory disease in feedlot cattle from which          pathogens such as Histophilus somni, M. haemolytica, M. bovis, and IBR virus isolated            from lung lesions.

 

Subclinical Infection (Bovine Virus Diarrhea)

 

         ·         Mild fever

         ·         Leukopenia

         ·         Inappetence

         ·         Mild diarrhoea

 

Clinical Signs - Mucosal disease (MD)

•      Unthrifty

•      Pyrexia

•      Depression, weakness, lameness

•      Anorexia, dehydration, hypersalivation

•      Mucopurulent nasal discharge

•      Lacrimation, corneal edema

•      Profuse watery diarrhea with tenesmus

•       Slow growers

Acute Mucosal Disease    

         ·         Clinical disease in animals: - At 6 to 24 months age of Post infection.

         ·         Morbidity rates: 44% and case–fatality rates:  100% reported in isolated herds

         ·         Fever 40°c to 41°c (104°f–105°f)

         ·         Tachycardia

         ·         Polypnea 

         ·         Ruminal contractions are usually absent

         ·         Depressed,

         ·         Anorexic

         ·         Drool saliva

         ·         Wetting hair around the mouth

         ·         Profuse and watery diarrhoea occurs in 2 to 4 days after the onset of clinical illness.

         ·         The faeces are foul smelling and also contain mucus or variable quantities of blood.

         ·         Fibrinous intestinal casts are present sometimes

         ·         Death occurs 5 to 7 days and per acute case death in few days.

Chronic Mucosal Disease    

        ·         Diarrhea

        ·         Inappetence

        ·         Progressive emaciation

        ·         Rough dry hair coat

        ·         Chronic bloat

         ·         Hoof deformities

         ·         Chronic erosions seen in the oral cavity and on the skin

 

Macroscopic Pathology

Bovine Viral diarrhea (BVD):

•      Mild erosions or shallow ulcerations observed at the oral cavity

          •      petechial and ecchymotic, haemorrhages of the sclera of the eyes 

Mucosal Disease (MD):

•      Erosions and ulcerations of mouth, tongue, esophagus, oral and ruminal papillae, abomasum, cecum/colon

•      Linear esophageal ulcerations

•      Peyer's patches swollen, necrohemorrhagic

•      Erosive-ulcerative interdigital dermatitis and coronitis

          •      oral cavity seen “cooked” appearance with the grayish colored necrotic epithelium which covering the deep-pink at raw base

 

Transplacental infections

•      Congenital defect in calves by BVD

•      Cerebellar hypoplasia

•      Microencephalopathy

•      Hypomyelination

•      Cataracts

•      Microphthalmia

•      Retinal degeneration

•      Optic neuritis

•      Thymic hypoplasia

•      Hypotrichosis/alopecia

•      Deranged osteogenesis

•      Mandibular brachygnathism

•      Growth retardation

•      Hydrocephalus

•      Hydroanencephaly

•      Porencephaly

 

Microscopic Pathology

•      Peyer’s patches:

ü  Severe, acute inflammation seen in overlying intestinal mucosa

ü  destruction of underlying glands

ü  collapse of lamina propria

ü  lymphocytolysis

•      fibrinoid necrosis or Hyaline degeneration of blood vessels:

ü  vasculitis in multiple organs accompanied by a mild-to-moderate mononuclear cell infiltrate in the vessel walls and perivascular tissues

•      Mesenteric lymph nodes and spleen:

ü  Lymphocytolysis and lymphoid depletion

•      Erosions in the skin are similar to those in the mucosa.

•      megakaryocyte myeloid cells seen in bone marrow infection

 

Diagnosis

•       Clinical signs

•        Laboratory tests

•       Virus isolation

•       Enzyme-linked immunosorbent assay (ELISA)

•       Immunohistochemistry – Skin PI animals

•       Real time polymerase chain reaction

•       Virus neutralization tests   

•      Viral antigen of MD can be detected in following tissues:-

1.    Lymph nodes

2.    Peyer’s patches

3.    Ileum and lymphoid tissue in the proximal colon

4.    Palatine tonsils

5.    Spleen

6.    Bronchiolar epithelial cells

7.    Crypts of the intestinal mucosa

8.    Salivary glands

9.    Tongue

10. Oesophagus

11. Skin

Treatment

 

         ·         Viral disease has no specific treatment.

         ·         We provided symptomatic treatment to animal.

           ·         Animals with chronic Bovine viral diarrhoea should be culled and destroyed.   

 

Prognosis

 

         ·         In severe cases of MD with marked oral lesions and profuse watery diarrhoea is unfavourable.

         ·         Slaughter for salvage or euthanasia should be considered as per veterinarian.