CALF SCOURS
Common viral causes are rotavirus and coronavirus. 1, 5

 

Rotavirus

Family: Reoviridae

    Rotaviruses are non-enveloped, medium sized viruses that have a double capsid structure and a segmented double-strand RNA genome.11

    Rotavirus is a primary player in the cause of diarrhea in many young animals, including calves.  Some rotaviruses can cross between species, but this is not very common.   It has 7 serogroups (A-G) which are further subdivided into serotypes neonatal diarrhea in North America.  The virus is stable in feces and relatively resistant to common disinfectants, therefore it is difficult to prevent contamination once infection has occurred. 1


Clinical Signs:
    An outbreak of rotaviral diarrhea usually occurs between the ages of 5-14 days, up to 3-4 weeks old.  Recovery from this diarrhea usually only takes a few days. 1, 5

 

Transmission:
    Rotavirus is spread through the feces, and to a lesser extent through the air if the relative humidity is in the medium range.  Therefore it is spread easily during calving season when calves come in frequent contact with adult cows and other calves.  The adult animals are the primary source of infection for the neonates, although it is ubiquitous in the environment.  50 – 100% of adult cattle test seropositive.  It should also be mentioned that infected calves not showing any clinical signs are also likely shedding the virus.  1


Morbidity and Mortality:
            A calf from a first calf heifer will have a higher incidence of morbidity and mortality because her passive transfer is not as strong due to having less circulating antibodies compared to an older cow.  Mortality is also increased in calves that did not receive sufficient colostral antibodies or with exposure to extreme cold weather.  1

Risk Factors:
-age (most susceptible at 1-3 weeks; related to decrease in
colostral antibodies)
-immune status of dam

-absorption of
colostral antibodies by calf
-amount of virus calf exposed to

-duration of time calf exposed to virus

-occurrence of stressful situations

-low ambient temperature

-presence of other
enteropathogens 1

Immunity:
    Newborns are only protected from rotaviruses by maternal antibodies for approximately 5-7 days.  This correlates with rotavirus diarrhea usually occurring 5-7 days after parturition, further coinciding with a decrease in colostral antibodies by day 3 after parturition and an incubation period of 12-24 hours.  Protection is not necessarily against infection, rather it is against developing clinical disease.   The animal will likely still shed virus in feces even though it is protected against clinical disease.  The amount of colostral antibody that the calf consumes also plays a big role in its protection against rotavirus.  Furthermore, the amount available in the lumen of the calf’s intestine to actively work against the rotavirus is important.  The amount of antibody in the colostrum is related to the amount of antibody in the dam’s serum, so a first calf heifer will not have as many antibodies in her serum because she has not been exposed to as many antigens in her lifetime as an older cow.1

Pathogenesis:

    Rotavirus infects mature cells in the small intestine, and to a lesser extent, the large intestine.  The infected cells are then sloughed and the absorptive surface is damaged for a few days until new cells can be made to replace the ones lost, although it may take up to twenty-one days for the absorbtive surface to return to normal.  One result of this is a reduction in the enzyme needed to breakdown lactose, a milk sugar.  Therefore lactose is not as well utilized by the animal.  The net effect of these changes imposed by the rotavirus is malabsorption which leads to diarrhea, dehydration, loss of electrolytes, and acidosis1

 

Diagnosis:
-Electron microscopy
-Immunofluorescence
-ELISA
-PCR
-Serology1
-and many more

Treatment:
    In the absence of complications, recovery from viral enteritis usually occurs without specific treatment in 2-5 days.  It is however common to give antibiotics to prevent/treat secondary bacterial infections.  Another practice that may help although it may not be that practical is to withhold milk for 24-48 hours.  If this is done, you will need to replace the milk with fluids and electrolytes to prevent dehydration, although this is something that you should be doing regardless of withholding milk or not.  The calf should also be isolated from the calving grounds if possible as well.  Using good hygiene and sanitation can minimize spread of the virus.  1



Control:
  1. Decrease infection pressure by decreasing population density to avoid overcrowding
  2. Ensure adequate colostrum intake
  3. Vaccinate dam to induce specific immunity in colostrums 1

 

Vaccination Options for Rotavirus:
  1. Oral vaccination containing MLV; efficacy uncertain because of maternal antibody interference
  2. Vaccinate dam during pregnancy to increase colostral antibodies

 

* Overall, vaccines are not particularly efficacious because of rapid decrease in colostral antibodies although they do cause a significant increase in the level and duration of colostral antibodies compared to animals that are not vaccinated.  1

 (SEE VACCINATIONS AVAILABLE)

 

Coronavirus

Family: Coronaviridae

    It is a single-stranded, enveloped RNA virus; the envelope has prominent droplet-shaped spikes which resemble solar corona.  11
   
    Coronavirus causes disease in beef calves worldwide, especially in the winter months.  Usually calves between 1-2 weeks old are affected, but the range is anywhere from 1 day to 3 months.  The virus is ubiquitious in cattle populations and the majority of cattle are seropositive.1

 

Clinical Signs:
    The bovine coronavirus causes acute diarrhea in calves and also has the capability to cause mild to moderate pneumonia.   Scours in these calves typically occurs between 1-2 weeks after parturition, but any calf between the ages of 1 day to 3 months can be affected.  Respiratory disease causes by coronavirus occurs anywhere from 2-16 weeks of age.1


Transmission:
    Coronavirus is spread through the feces, and to a lesser extent through the air if the relative humidity is in the medium range.  Therefore it is spread easily during calving season when calves come in frequent contact with adult cows and other calves.  The adult animals are the primary source of infection for the neonates.  The majority of adult cattle test seropositive.  It is often present in calves that show no clinical signs as well as those that are showing them.  It is shed by up to 70% of cows with the incidence of shedding increasing in the winter months and just before parturition in North America.  It is also shed by those showing that do show clinical signs as well as those who do not.  Notably, bovine coronavirus has also been isolated fro wild ruminants with diarrhea, therefore they may be an important source for the spread of infection of this virus as well.1

Morbidity and Mortality:
    A calf from a first calf heifer will have a higher incidence of morbidity and mortality because her passive transfer is not as strong due to having less circulating antibodies compared to an older cow.  Mortality is also increased in calves that did not receive sufficient colostral antibodies or with exposure to extreme cold weather.1


Risk Factors:
-age (most susceptible at 1-3 weeks; related to decrease in colostral antibodies)
-immune status of dam
-absorption of colostral antibodies by calf
-amount of virus calf exposed to
-duration of time calf exposed to virus
-occurrence of stressful situations
-low ambient temperature
-presence of other enteropathogens 1



Immunity:

   
Newborns are only protected from coronaviruses by maternal antibodies for approximately 5-7 days.  This correlates with coronavirus diarrhea usually occurring 5-7 days after parturition, further coinciding with a decrease in colostral antibodies by day 3 after parturition and an incubation period of 12-24 hours.  Protection is not necessarily against infection, rather it is against developing clinical disease.   The animal will likely still shed virus in feces even though it is protected against clinical disease.  
The amount of colostral antibody that the calf consumes also plays a big role in its protection against rotavirus.  Furthermore, the amount available in the lumen of the calf’s intestine to actively work against the rotavirus is important.  The amount of antibody in the colostrum is related to the amount of antibody in the dam’s serum, so a first calf heifer will not have as many antibodies in her serum because she has not been exposed to as many antigens in her lifetime as an older cow.  1


Pathogenesis:

    Coronavirus infects mature cells in the small intestine, and to a lesser extent, the large intestine.  The infected cells are then sloughed and the absorptive surface is damaged for a few days until new cells can be made to replace the ones lost, although it may take up to twenty-one days for the absorbtive surface to return to normal.  One result of this is a reduction in the enzyme needed to breakdown lactose, a milk sugar.  Therefore lactose is not as well utilized by the animal.  The net effect of these changes imposed by the rotavirus is malabsorption which leads to diarrhea, dehydration, loss of electrolytes, and acidosis.1

 


Diagnosis:
-Electron microscopy
-Immunofluorescence
-ELISA
-PCR
-Serology1
-and many more 

 

Treatment:
    In the absence of complications, recovery from viral enteritis usually occurs without specific treatment in 2-5 days.  It is however common to give antibiotics to prevent/treat secondary bacterial infections.  Another practice that may help although it may not be that practical is to withhold milk for 24-48 hours.  If this is done, you will need to replace the milk with fluids and electrolytes to prevent dehydration, although this is something that you should be doing regardless of withholding milk or not.  The calf should also be isolated from the calving grounds if possible as well.  Using good hygiene and sanitation can minimize spread of the virus.1

 

Control:
    1.  Decrease infection pressure by decreasing population density to avoid overcrowding

    2. 
Ensure adequate colostrum intake
    3.  Vaccinate dam to induce specific immunity in colostrums 1

 

Vaccination Options For Coronavirus:
    Vaccinating for coronavirus will not decrease the amount of shedding in the winter months, but studies have shown it to decrease shedding prior to parturition, unlike in a non-vaccinated cow where shedding increases at this time.1

(SEE VACCINATIONS AVAILABLE)

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