Torque teno virus (TTV)

Question 1

TTV trials

Answer 1

1. VIGILung - lung transplant patients in Germany and Austria - Tacrolimus dose adjustment based on TTV levels
2. TTV-GUIDE IT - 16 transplant centres in Europe - adjusting tacrolimus levels in kidney transplant

Question 2

TTV structure and classification

Answer 2

Small non-enveloped circular (-)ssDNA

5 genogroups and 50 genotypes.

Genome has 4 ORFs. The untranslated region (UTR) is preserved between genotypes and it’s the PCR target.

Anellovirus family - Torque teno minivirus (TTMV) and Torque teno midivirus (TTMDV)

Baltimore: II

Question 3

TTV epidemiology and transmission

Answer 3

2-90% individuals infected

Breast milk, saliva, faeco oral, droplets, blood transfusions.

Question 4

TTV replication & reservoir

Answer 4

Roling circle replication

TTV reservoir - T lymphocytes. So T cell depleting therapy brings down VL and hence it is a less useful marker in transplant when these agents are used.

Question 5

Negative vs positive TTV PCR in SOT

Answer 5

Negative:
1. Non infected
2. Lymphopenic
3. Cleared infection
4. Genotype not being able to be picked up on the PCR used

Positive:
1. Low TTV loads - association with organ rejection
2. High TTV loads - associated with infections