Porcine rotavirus continues to plague the global pig industry
Tips for diagnosis, prevention and control
26 April 2023
7 minute read
By: Rotaviruses are a primary cause of diarrhea in nursing and post-weaned pigs in commercial swine operations, affecting the pig’s small intestine. Uncomplicated cases of diarrhea caused by rotavirus are typically accompanied by high morbidity but low mortality. There’s no question that piglet diarrhea caused by rotavirus leads to productivity losses and thus causes economic losses in the global pork industry [1]. Australia has put an annual price tag of more than AU$7 million (US$4.8 million) on piglet scours [2].
The different rotavirus groups
At least 10 antigenically distinct serogroups of rotaviruses (A, B, C, D, E, F, G, H, I, and J) exist, and five of them (A, B, C, E, and H) affect swine [3].
- Group A rotaviruses are by far the most frequently detected, and more is known about this group.
- Group B strains are poorly characterized, and research indicates they are found in the US and Brazil but more often when other species like Groups A and C are present [4].
- Group C is more common in nursing pigs that are 1–10 days old. It is commonly found in contaminated environments, and its prevalence is growing in the US, Canada, and Brazil.
- Group E rotaviruses were first diagnosed in the UK but are rarely reported, and when found they have been of low pathological relevance [5].
- Group H is considered an emerging pathogen and has been detected in pigs with and without diarrhea. It has also been found in humans and bats [6].
Rotaviruses belong to the Reoviridae family. They are non-enveloped, double-stranded RNA viruses with a segmented genome. Cross-protective immunity is not found between serogroups.
Rotaviruses are very stable in the environment, allowing them to survive under normal environmental conditions for long periods of time. They are resistant to temperature changes, many chemicals, different pH levels, and many commonly used disinfectants. Recommended disinfectants for cleaned surfaces include formaldehyde and chlorine-based disinfectants [1]. Because rotaviruses persist in the environment, they account for widespread infection and are therefore a constant risk of disease to piglets.
What does rotavirus look like on-farm?
Rotavirus diarrhea may be white or yellow stool that starts out as liquid, but in uncomplicated cases becomes creamy and then pasty before the stool returns to normal. This process may occur over 2 hours to several days.
Diarrhea symptoms usually occur in nursing piglets and weaned pigs, with decreasing severity up to the age of 6 weeks old. However, pigs of all ages are susceptible to rotavirus infection. The age of highest incidence differs by rotavirus group and management conditions.
The following indicate possible signs of a rotavirus infection [7]:
Sows
- Short-term diarrhea
- May or may not show signs of disease
Piglets
- Watery, profuse diarrhea
- Villus atrophy is a consistent feature with dehydration, malabsorption, and wasting
- Diarrhea persists for 3–4 days
- Pig looks hollow in the abdomen and becomes dehydrated
- Sunken eyes
- Wet skin around the rectum
Weaners and growers
- Watery, profuse diarrhea appears after piglets are 7–10 days of age, and it becomes progressively less important with age
- If pathogenic strains of coli are present, severe disease can occur with heavy mortality
- Villus atrophy is a consistent feature that results in malabsorption
- Dehydration
- Diarrhea lasts 3–4 days
- Pig looks hollow
- Sunken eyes
- Wet skin around the rectum
Rotavirus infection in post-weaned pigs is considered less important, but it is often identified when testing for acute E. coli diarrhea that occurs in the first 7–10 days after weaning.
How does rotavirus impact pigs’ intestines and health?
Rotaviruses replicate in the mature enterocytes (intestinal absorptive cells) that line the small intestine. Enterocytes cover the villi, which are millions of finger-like structures that sit on the inside lining of the small intestine. As infection occurs, the cells are destroyed, and the villi shrink into short, blunt structures that limit or do not allow for nutrient absorption.
Therefore, much of the ingested milk that a rotavirus-infected nursing piglet receives will pass through the gut without being digested or absorbed into the piglet’s stomach or intestines. This has two effects:
- It provides a nutritional source in the piglet’s stool for harmful bacteria that can cause secondary disease.
- It creates an osmotic effect in the intestine that may exacerbate diarrhea and dehydration, resulting in loss of water, electrolytes, and body weight, and sometimes death.
Villi can die within 24–36 hours, but regeneration of the intestinal villi and recovery of normal digestive capacities are possible and usually take about 7 to 10 days in nursing piglets [5].
Diagnosing rotavirus
When a farm experiences a diarrhea problem in pigs of 10–40 days of age, rotavirus infection, either as a primary or secondary agent, must be considered. Farm history and diarrhea symptoms are important, but diagnostic testing is needed to confirm the pathogenic cause. To confirm a diagnosis, several laboratory techniques are typically used in combination, including histopathology, fluorescence in situ hybridization (FISH), immunohistochemistry, reverse-transcription polymerase chain reaction (RT-PCR), and enzyme-linked immunosorbent assay (ELISA) [1,5].
Acutely infected pigs will have higher levels of viral shedding, so obtaining fecal or intestinal-section samples within 24 hours of the onset of diarrhea is optimal. Because most pigs are positive for rotavirus antibodies, blood samples are not used in diagnosis. Ideally, laboratory testing should also include assays to detect the presence of E. coli, Isospora suis (coccidiosis), coronaviruses including enzootic transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), and any other agents causing a similar diarrheal syndrome. If these co-infections are found, increased disease severity and mortality should be expected [5].
Prevention and control
There is no proven specific treatment for rotaviral infection in young piglets, but supportive therapy as well as good husbandry and biosecurity measures can help piglets with rotavirus. Supportive therapy may include adding electrolytes in drinking water and providing a warm, dry environment and good nutrition based on the age of the pig. Antibiotic therapy may be recommended by a veterinarian for bacterial co-infections, but it’s not an effective treatment for rotavirus.
If rotavirus outbreaks are a consistent issue on-farm, the following actions should be considered to break the disease cycle:
- Switch to an all-in/all-out management system in farrowing and nursery units
- Design floors and barn surfaces for comprehensive cleaning and disinfection between farrowings to lower exposure and virus load
- Disinfect processing equipment between litters
- Reduce pig handling and pig movement
- Change gloves frequently
- Institute a shorter farrowing period, which results in less buildup of rotaviruses
Modified live and killed rotavirus vaccines are available in some countries. These vaccines typically protect only against Group A rotaviruses and are stacked to protect against other diarrheal diseases. Sows and gilts can be vaccinated prior to farrowing to stimulate the production of antibodies in their colostrum and milk, which should protect piglets until they can develop their own immunity. Feedback inoculum is another common method that exposes adult sows to rotaviruses to induce immunity.
Importance of piglet immunity
Because most if not all sows are positive for rotavirus antibodies, they will transfer a variable amount of passive immunity to their nursing pigs via colostrum and milk. Therefore, it is essential that neonatal pigs receive adequate colostrum and milk.
Several factors may interfere with passive immunity and allow rotavirus clinical infections to take hold in piglets, including [8]:
- Failure to nurse and ingest enough colostrum at frequent intervals shortly after birth
- Failure of the sow to provide enough milk to piglets less than a week old
- High doses of virus due to a contaminated environment may exceed the protective effect ofantibodies in the milk
- Ingestion of creep feed and water by 2- to 3-week-old nursing pigs may dilute the level of protective antibodies
- Weaning, which results in complete loss of protective milk antibodies and may bring on a second episode post-weaning
Producers should consider protecting pigs against rotavirus, prior to weaning, through active immunization if there is a vaccine available for the group and the serotypes/genotypes of porcine rotavirus that are circulating on the farm [5].
References
[1] Rotaviral Enteritis | Iowa State University. Vetmed.Iastate.Edu (2023). https://vetmed.iastate.edu/vdp...
[2] Piglet Scours | Business Queensland. Business.Qld.Gov.Au (2023). https://www.business.qld.gov.a...
[3] Chepngeno J, Diaz A, Paim FC et al. Rotavirus C: prevalence in suckling piglets and development of virus-like particles to assess the influence of maternal immunity on the disease development. Vet Res 50:84 (2019). https://doi.org/10.1186/s13567...
[4] Miyabe FM, Dall Agnol AM, Leme RA et al. Porcine rotavirus B as primary causative agent of diarrhea outbreaks in newborn piglets. Sci Rep 10:22002 (2020). https://doi.org/10.1038/s41598...
[5] Saif L, Vlasova A. Rotaviral diarrhea in Pigs. Pork Information Gateway (2022). Available at: https://porkgateway.org/resour...
[6] Flores PS, Costa FB, Amorim AR, et al. Rotavirus A, C, and H in Brazilian pigs: potential for zoonotic transmission of RVA. Journal of Veterinary Diagnostic Investigation. 33(1):129-135 (2021). doi:10.1177/1040638720967673
[7] Disease Guide: Rotavirus Infection. ThePigSite.com (2018). https://www.ThePigSite.com/dis...
[8] Rotaviral Diarrhoea in Pigs. ThePigSite.com (2013). https://www.thepigsite.com/art...
For Research Use Only. Not For Use in Diagnostic Procedures.
