virology blog
About viruses and viral disease
Viruses and bacteria are both present at mucosal surfaces and it is not surprising that they interact in many ways. Sometimes members of the gut microbiome help viruses to infect cells, exemplified by poliovirus, reovirus, and mouse mammary tumor virus. The opposite also happens: segmented filamentous bacteria can prevent and cure rotavirus infection.
[Read more…] about Segmented filamentous bacteria block rotavirus infection
The US Food and Drug Administration has updated its recommendations on both Rotarix and RotaTeq, vaccines for the prevention of rotavirus disease in infants:
Based on careful evaluation of a variety of scientific information, FDA has determined it is appropriate for clinicians and health care professionals to resume the use of Rotarix and to continue the use of RotaTeq.
In making its recommendation, the FDA considered the strong safety records of both vaccines, including clinical trials in tens of thousands of individuals and the use of the vaccines in millions of recipients. There is no evidence that either porcine circovirus type 1 or type 2 poses a safety risk to humans, and neither virus is known to infect humans or cause disease.
The FDA also noted that the benefits of the rotavirus vaccines are considerable and outweigh the small theoretical risk of the viral contaminant.
The product labels will be updated to reflect the fact that the vaccine contains a PCV contaminant. In addition, GlaxoSmithKline will rederive Rotarix so that it does not contain PCV. Merck has not yet made a decision about whether they should produce a PCV-free rotavirus vaccine. But if my suggestion carries any weight at Merck (I know it does not), they should not hesitate to follow GlaxoSmithKline’s lead.
The US Food and Drug Administration has recommended that administration of the Rotarix vaccine, which protects against rotavirus infection, be suspended. This action comes after an independent research group found that the vaccine contains DNA of porcine circovirus type 1.
Rotaviruses are the single leading cause of diarrhea in infants and young children. Each year rotavirus gastroenteritis causes over 1,250,000 episodes of diarrhea and 527,000 deaths, mainly in developing countries. Rotavirus vaccines are used to reduce the global burden of rotavirus disease. Rotarix, the vaccine manufactured by GlaxoSmithKline, is an infectious, attenuated vaccine that is administered orally to infants.
The genetic information of rotaviruses consists of 11 segments of double-stranded RNA. In contrast, porcine circoviruses are small viruses with a circular, single stranded DNA genome (pictured). At 1.7 kb in length, the DNA is among the smallest known viral genomes and encodes only two proteins. Porcine circovirus 1 was originally discovered as a contaminant of a pig kidney cell line. Later a second strain, porcine circovirus 2, was isolated and shown to be associated with postweaning multisystemic wasting disease, an emerging disease of swine.
Porcine circovirus 1 DNA was also found in the cells used to produce Rotarix. Therefore the contaminant has been present since the early days of vaccine development, including clinical trials. A different rotavirus vaccine produced by Merck, called RotaTeq, does not contain porcine circovirus DNA.
It’s not at all clear that the presence of porcine circovirus 1 DNA in Rotarix is a problem. Circoviruses have not been associated with human disease, and porcine circovirus 1 has not been found to cause disease in any animal. Many humans have antibodies to these viruses, including porcine circovirus, indicating that they were infected at one time. Furthermore, it’s not known if the vaccine contains infectious virus or DNA fragments. Nevertheless, it’s always preferable to err on the side of caution, as the FDA has done.
Because porcine circoviruses are widespread in commercial swine populations, there have been concerns about the use of porcine organs for xenotransplantation and for the production of products used in humans such as factor VIII, heparin, insulin and pepsin. It is therefore important to ensure that such products do not contain infectious circoviruses.
This incident will undoubtedly further increase public distrust of vaccines and vaccine manufacturers. I have not yet seen the journal article describing these findings, so I can’t comment on why the contaminant was not identified early in vaccine development. According to the FDA, “In four to six weeks, FDA will convene an expert advisory committee and make additional recommendations on the use of rotavirus vaccines.” If Rotarix is found to contain infectious porcine circovirus, then its use will certainly be discontinued. However, detection of small noninfectious fragments of porcine circovirus DNA Rotarix will likely lead to resumption of vaccine use. In either case, new lots of vaccine should be produced using circovirus-free cells.
Tischer I, Bode L, Apodaca J, Timm H, Peters D, Rasch R, Pociuli S, & Gerike E (1995). Presence of antibodies reacting with porcine circovirus in sera of humans, mice, and cattle. Archives of virology, 140 (8), 1427-39 PMID: 7544971
Fenaux M, Opriessnig T, Halbur PG, Xu Y, Potts B, & Meng XJ (2004). Detection and in vitro and in vivo characterization of porcine circovirus DNA from a porcine-derived commercial pepsin product. The Journal of general virology, 85 (Pt 11), 3377-82 PMID: 15483254
From Georgia State University, Vincent speaks with Chris, Andrew, Priya, and Richard about their careers and their work on Ebolaviruses, rotavirus, and antiviral drug development.
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by Gertrud U. Rey
Type 1 diabetes is an organ-specific autoimmune disease that is characterized by the loss of insulin-producing beta cells in the pancreas. The loss of these cells leads to decreased insulin production (hypoinsulinemia) and increased levels of glucose in the blood (hyperglycemia). While it is still unclear what exactly causes the loss of beta cells, experts agree that it is likely a combination of genetic and environmental factors. An increasing body of evidence suggests that Coxsackievirus strain B4 is an environmental trigger, because it specifically targets beta cells, causing them to die.
From the 13th International Symposium on dsRNA viruses in Belgium, Vincent speaks with Harry Greenberg about his career and his work on rotaviruses, noroviruses, hepatitis B virus, and influenza virus.
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From Indiana University, Vincent and Kathy speak with Tuli Mukhopadhyay, John Patton, and Adam Zlotnick about their careers and their work on alphaviruses, hepatitis B virus, and rotaviruses.
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Did you ever wonder what different virus infections you have had in your lifetime? Now you can find out with just a drop of your blood and about $25.
Immune defense systems of many hosts produce antibodies in response to virus infections. These large proteins, which are generally virus specific, can block or inhibit virus infection, and persist at low levels for many years after the initial infection. Hence it is possible to determine whether an individual has had a virus infection by looking for anti-viral antibodies in the blood. Up to now the process of identifying such antibodies has been slow and limited to one or a few viruses. A new assay called VirScan allows unbiased searches for all the virus antibodies in your blood, providing a picture of all your past infections.
To identify the human antivirome, DNAs were synthesized encoding proteins from all viruses known to infect humans – 206 species and over 1000 strains. These DNAs were inserted into the genome of a bacteriophage, so that upon infecting bacteria, the viral peptides are displayed on the phage capsid. These ‘display’ phages were then mixed with human serum, and those that were bound by antibodies were isolated. The DNA sequence of the phage genomes were then determined to identify the human virus bound by the antibodies.
This method was used to assay samples from 569 humans. The results show that each person had been exposed to an average of 10 viruses, with a range from a few to over 20 (two individuals had antibodies to 84 different virus species!). The most frequently identified viruses included herpesviruses, rhinoviruses, adenoviruses, influenza viruses, respiratory syncytial virus, and enteroviruses. The overall winner, found in 88% of samples, is Epstein-Barr virus.
These results are not unexpected: all of us are infected with at least a dozen viruses at any time, and the viruses identified in this study known to infect much of the human population. What was surprising is the absence of some common viruses, such as rotaviruses, and the ubiquitous polyomaviruses. According to serological surveys, the most common human viruses are the small, single-stranded DNA containing anelloviruses. Yet the related torque teno virus was only found in 1.7% of samples. These differences are likely due to a combination of technical and biological issues (e.g., failure of antibodies to certain viruses to persist in serum).
This new assay may one day become a routine diagnostic tool that is used along with complete blood counts and chemistries to know if a patient’s signs and symptoms might be attributable to a past virus infection. VirScan technology is not limited to virus infections – it can be used to provide a history of bouts with bacteria, fungi, and parasites.
VirScan might also allow us to determine which virus infections are beneficial, and which contribute to chronic diseases such as autoimmune or neurodevelopmental disorders or cancer. The assay can be used to conduct unbiased population-based studies of the prevalence of virus infections and their possible association with these diseases. Such connections were not previously possible with antibody assays that search for one virus at a time. This approach was not only inefficient, but required guessing the responsible virus.
Some other findings of this study are noteworthy. As expected, children had fewer virus infections than adults. HIV-positive individuals had antibodies to more viruses than HIV-negative individuals, also expected given the damage done by this virus to the immune system. Frequencies of anti-viral antibodies were higher outside of the United States, possible due to differences in genetics, sanitation, or population density. In most samples, there was a single dominant peptide per virus, although there were occasional differences among populations. This information might be useful for improving vaccines, or tailoring them to specific countries or regions.
Update: It would be very informative to use VirScan to search for antibodies against viruses that are not known to infect humans. Other animal viruses, plant viruses, insect viruses: to which do a significant fraction of humans respond? The information might identify other viruses that replicate in humans and which might constitute future threats (or present benefits).
On episode #285 of the science show This Week in Virology, Vincent meets up with XJ Meng and Sarah McDonald at Virginia Tech to talk about their work on viruses of swine and rotaviruses.
You can find TWiV #285 at www.microbe.tv/twiv.
Recently thousands of dead and decaying pigs were pulled from rivers in Shanghai and Jiaxing, China. Apparently farmers dumped the animals into the water after the pigs became ill. Porcine circovirus has been detected in the in pig carcasses and in the water.
Porcine circoviruses are small, icosahedral viruses that were discovered in 1974 as contaminants of a porcine kidney cell line. They were later called circoviruses when their genome was found to be a circular, single-stranded DNA molecule. Upon entry into cells, the viral ssDNA genome enters the nucleus where it is made double-stranded by host enzymes. It is then transcribed by host RNA polymerase II to form mRNAs that are translated into viral proteins. There is some evidence that circoviruses might have evolved from a plant virus that switched hosts and then recombined with a picorna-like virus.
Porcine circoviruses are classified in the Circoviridae family, which contains two genera, Circovirus and Gyrovirus. There are two porcine circoviruses, PCV-1 and PCV-2; only the latter causes disease in pigs. Infection probably occurs via oral and respiratory routes, and leads to various diseases including postweaning multisystemic wasting syndrome, and porcine dermatitis and nephropathy syndrome. Virions are shed in respiratory and oral secretions, urine, and feces of infected pigs. Other circoviruses may cause diseases of birds, including psittacine beak and feather disease, and chicken infectious anemia, the latter caused by the sole member of the Gyrovirus genus. There are also circoviruses that infect canaries, ducks, finches, geese, gulls, pigeons, starlings, and swans.
We have no good evidence that porcine or avian circoviruses can infect humans. In the United States, porcine circovirus sequences can be detected in human feces. These most likely originate from consumption of pork products, most of which also contain porcine circoviruses. Circovirus sequences have also been found in commonly eaten animals such as cows, goats, sheep, camels, and chickens. Outside of the United States, the circoviruses found in human stools do not appear to be derived by meat consumption and might cause enteric infections.
Recently both PCV-1 and PCV-2 sequences were detected in Rotarix and RotaTeq, vaccines for the prevention of rotavirus disease in infants. The source of the contaminant was trypsin, an enzyme purified from porcine pancreas, which is used in the production of cell cultures used for vaccine production. Use of these vaccines was temporarily suspended, but resumed when the Food and Drug Administration concluded that there is no evidence that porcine circoviruses pose a safety risk to humans.
The good news is that porcine circoviruses in Shanghai’s waters are no danger to humans. But it is not a good idea to have rotting pig carcasses in a river that supplies some of Shanghai’s drinking water.