Circovirus Family Facts



Molecular Biology


Additional Links


Circoviridae Vaccine:

Vaccine trials against porcine circoviruses that have been conducted in the last few years have proved extremely successful. In pigs and hogs, circovirus is shed through urine, feces, colostrum, semen as well as nasal and oral secretions. Infection results in symptoms such as rapid weight loss, diarrhea, respiratory problems, lethargy, anorexia, and skin discolorations or lesions. Study results  suggest that the vaccine developed is effective in limiting porcine circovirus type 2-associated disease in pigs and was recently licensed by the USDA.  

(Above: An image of procine circovirus infection)

Transfusion Transmitted Virus  or Torque Teno virus or TTV

An unusual feature of the human circoviruses, Torque Teno virus (TTV) and Torque Teno-like Mini Virus (TLMV), is the incredible genetic diversity of virus isolates that can be detected in a single infected individual.   Sequencing of viral isolates has determined more than 40% genetic differences in virus from a single infected human.  Infection with different strains of the virus, as well as viral quasi-species, is also very common in infected humans.

The History of TTV:

TT virus (TTV) is the first member of circoviruses identified to infect humans. It was initially identified in Japanese patients presenting with hepatitis of unknown cause in 1997. Initially sequence analysis of TTV suggested to scientists that it was a virus belonging to the family, Parvoviridae. However, at the end of 1998, two separate studies confirmed that it in fact belonged in the Circovirus family due to its circular genome and GC-rich additional region.

(Above: An illustration of the TTV circularized genome)  

Porcine Circoviruses - The Smallest Autonomous Viruses!

Porcine Circoviruses (PCV) are the smallest known viruses that can replicated autonomously in eukaryotic cells. The single-stranded DNA genomes of these viruses comprise less than 1800 nucleotides and encode just two major open reading frames. Because of their limited coding capacity, all circoviruses rely significantly on the host cell's machinery. There are two types of PCV are known, differentiated by their pathogenicity. Porcine circovirus type 1 (PCV1) is an orphan virus. Porcine circovirus type 2 (PCV2) causes Postweaning Multisystemic Wasting Syndrome (PMWS), an emerging and multifactorial swine disease. Both PCV1 and PCV2 show sequence homology; however, the distinct pathogenicity between the two is distinctly differentiating.  

TTV and Cancer

TTV infection is  widespread particularly among patients with liver disease, including cryptogenic cirrhosis and fulminant hepatic failure, although it is often asymptomatic in healthy individuals. Several studies have shown that TTV is more common in patients with liver cirrhosis and hepatocellular carcinoma than it is even in those with chronic hepatitis, suggesting that infection with TTV might act as a co-factor for development of these cancers. 

(Above: Liver Cirrhosis)