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Rotavirus In Animals

Rotavirus, which is a genus within the family Reoviridae, is among the most important etiological agents of severe diarrheal illness in humans and animals around the world. The genome of this pathogen, consisting of 11 segments of double-stranded ribonucleic acid (RNA), is characterized by genetic variability including point mutations, genomic reassortment, and genome rearrangements that lead to its considerable diversity.

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Animal rotaviruses are considered potential reservoirs for genetic exchange with human rotaviruses. There is now increasing evidence that animal rotaviruses can infect humans, either through direct transmission of the virus or by contributing one or several genes to reassortants with essentially a human strain genetic background.

Types of animal rotaviruses

Based on the antigenic sites located on the VP6 protein of the inner capsid, rotavirus strains are classified into five main (A, B, C, D, E) and two additional tentative (F, G) serotype groups, which are also known as serogroups. The rotavirus strains classified into serogroups A, B, and C are pathogenic for humans and various animal species.

The most virulent and commonly isolated strains belong to serogroup A and are known to cause acute infectious diarrhea in children, as well as various domestic mammalian and avian species. Serogroup B has been mainly associated with diarrhea in neonatal lambs, whereas Serogroup E strains have been isolated only from pigs. Serogroup D, F, and G strains have been isolated only from avian species.

In 1969, bovine rotavirus was the first group A rotavirus isolated in cell culture and confirmed as a cause of diarrhea in calves. The virulence of the strain and the age of the calf are important parameters in the pathogenesis of a rotaviral infection. Replacement of villous enterocytes is slow in newborn calves, which means that newborn calves are susceptible to disease caused by strains that are only moderately virulent.

Avian rotaviruses represent a diverse group of intestinal viruses, which may induce subclinical manifestations. However, these avian rotaviruses can also cause several diseases in poultry with symptoms of diarrhea, growth retardation, or runting and stunting syndromes. The latter can result in increases in feed conversion ratios and large economic losses to the poultry industry.

Rotaviruses can be found in virtually all pig populations; therefore, the detection of the virus in the feces does not entail a definite diagnosis. Neonatal and susceptible young growing pigs are exposed to viruses that are shed by carriers, including sows, or through exposure to the virus in their environment. The severity of the young pigs' clinical presentation depends on the dose ingested and the number of protective antibodies present in the dam's colostrum and milk.

Group A rotaviruses have been isolated from dogs and cats, with a high seroprevalence in adult animals. Although the disease appears to be uncommon, mild enteritis is sometimes observed in young puppies less than 12 weeks of age. Canine rotaviruses appear to group together with the G3P[3] rotavirus strains.

Zoonotic potential

A large number of people are exposed to animal rotaviruses every year. Results of serological assays and nucleotide chain recognition methods have shown that many strains of rotaviruses isolated from mammalian species have the ability to infect humans. Furthermore, there has been strong evidence on the zoonotic transfer of avian strains.

Different examples of identical or (almost identical) transfer of animal rotaviral segments of the virus to humans are described in the literature. Most of these viruses refer to segments isolated from cattle or pigs, which have been detected primarily in developing countries with a close cohabitation of humans and animals. In the majority of cases, infection of humans by segments of animal origin leads to mild clinical disease.

Most domestic animal species can play a role in the spread of the virus by acting as natural reservoirs of the virus or as intermediate or end hosts. Due to the ability of the virus to overcome the barriers between species, it is also clear that animal strains may act as a natural source of viral genomes, thus promoting mutations and creating new viral genotypes with unknown virulence.

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Phylogenetic analyses of the rotavirus genome expose repeated intersections between the evolution of human and animal rotavirus strains, possibly as a consequence of multiple events of transmission between various animal species. The interspecies transmission and subsequent gene reassortment are significant mechanisms that drive the diversity of rotaviruses and enable the emergence of new pathogenic strains.

As mixed infections are a prerequisite for reassortment events, joint surveillance of animal and human rotavirus strains will be pivotal in gaining a better understanding of the relationships between co-circulating viruses, as well as assessing any relevant vaccination programs.

References Further Reading

Vaccine Kicked Rotavirus To The Curb In A Few Short Years

Within six years of the introduction of the rotavirus vaccine, hospitalizations for the diarrheal illness had dropped by 94% and hospitalizations for overall gastrointestinal illnesses were cut in half. Those are the findings of CDC-funded research published in JAMA today.

The first vaccine, RotaTeq by Merck , was introduced in 2006, followed by Rotarix by GlaxoSmithKline in 2008, so there were not exactly major changes to sanitation or a sudden improvement in medical care during that time of the vaccines' introduction. In fact, the decline in rotavirus cases may be underestimated because so few of the gastrointestinal hospitalizations included testing for it, meaning many cases were likely missed.

"Yet again we are seeing just how effective our immunization programs are at reducing the risk of illness in vulnerable populations," said Clay Jones, a neonatal hospitalist at Newton–Wellesley Hospital in Newton, Massachusetts, who was not involved in the study. "This study should inspire further efforts to improve the rates of rotavirus immunization in young children."

Rotavirus is a gastrointestinal illness that typically causes severe vomiting and diarrhea for about a week, putting children at high risk for dehydration. In the U.S., where resources are usually abundant, children do not usually die from the disease. The World Health Organization, however, estimated in 2004, before the vaccine was introduced, that half million children a year died from the disease.

"Rotavirus kills hundreds of thousands of children under the age of five every year, but we are lucky to live in a country where fatal outcomes are a fraction of those seen around the world," Jones said. "But it is still a terrible illness which brings with it a great burden on society."

A nurse gives the rotavirus vaccine to a baby during a program to start vaccination against... [+] rotavirus. The vaccine is for children aged 6 weeks to 6 months of age, to prevent diarrhea caused by rotavirus. This is the first time that the vaccine is provided in Haiti massively and free, and is organized by the Ministry of Public Health and Population of Haiti, with support from PAHO/WHO in Port au Prince, on April 29, 2014. AFP PHOTO/Hector RETAMAL/Getty Images)

The track record for the rotavirus vaccine has already been strong, and some past research has even found strong evidence for the effect of herd immunity in preventing the illness even among children who had not received the vaccine. But this study is among the largest to look at the overall effect of the vaccine's introduction across the U.S. Researchers at the CDC analyzed de-identified records of hospital admissions in an inpatient database for the 26 states who reported their hospital discharge data every year from 2000 through 2012.

Among more than 1.2 million cases of gastrointestinal illnesses in children under 5 during those years, about 17% were specifically diagnosed with rotavirus. But since many children with GI infections do not receive testing for rotavirus, the researchers compared the pre-vaccine cases (2000-2006) with the post-vaccine cases (2008-2012) for both rotavirus and for general GI hospitalizations.

The drop in the years after the vaccine's introduction is dramatic: rotavirus cases went from 16 per 10,000 children in the pre-vaccine era to 5-6 cases per 10,000 in the couple years after the vaccine to 1 case per 10,000 children a year in 2012, the year when vaccine coverage was the highest. The decline ranged from 63% to 94% lower than the rate before 2007.

Similarly, hospitalizations for any kind of GI infection went from 76 cases per 10,000 children before the vaccine to 34 cases per 10,000 children in 2012. The cases dropped by nearly a third in 2008, the year after the vaccine had been out for at least a full year, and hit their lowest in 2012, when GI hospitalizations were 55% lower than they were in the pre-vaccine first half of the 2000s.

"Pediatric healthcare professionals already tend to shout from the rooftops about vaccine safety and efficacy," Jones said. "This study isn't surprising given what we already know, but it's still great news and something which needs to be shared with vaccine hesitant caregivers."

The most serious risk of the rotavirus vaccine is a bowel obstruction disorder called intussusception, estimated to occur as often as 1 in 20,000 doses of the vaccine. You can find here an in-depth examination of the risks and benefits of the vaccine with regards to intussusception, including typical treatments and outcomes for both rotavirus and the bowel disorder.

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