A virus closely related to HTLV-I, human T-lymphotropic virus 2 (HTLV-II) shares approximately 70% genomic homology (structural similarity) with HTLV-I. It was discovered by Robert Gallo and colleagues.[1][2]
A phylogeny of the subtypes of HTLV and their relationships between endogenous and exogenous retroviruses in the human genome. HERV = human endogenous retrovirus, SFV = simian foamy virus
Virology
HTLV-1 and HTLV-2 share broad similarities in their overall genetic organization and expression pattern, but they differ substantially in their pathogenic properties.[3] The virus utilizes the GLUT-1 and NRP1 cellular receptors for their entry, although HTLV-1, but not HTLV-2, is dependent on heparan sulfate proteoglycans. Cell-to-cell transmission is essential for virus replication and occurs through the formation of a virological synapse.[3] The family of Human T-lymphotropic virus (Figure 2) can be further categorized into four sub types. The figure also divides the retroviruses into exogenous and endogenous. Retroviruses can exist as two different forms: endogenous which consist of normal genetic components and exogenous which are horizontally transferred genetic components that are usually infectious agents that cause disease i.e. HIV. In (Figure 3) open reading frames (ORF) are shown which can if translated can predict which genes will be present and this can help to better understand human retroviruses. Of the four subtypes, HTLV-2 may be linked to Cutaneous T-cell lymphoma (CTCL).[5] In one study involving cultured lymphocytes from patients with mycosis fungoides (Figure 1), PCR amplification showed gene sequences of HTLV-II. This finding may suggest a possible correlation with HTLV-2 and CTCL. Further research and studies must be conducted to show a positive relationship.[1]
HTLV-1 and HTLV-2 are both involved in actively spreading epidemics, affecting 15-20 million people worldwide. [4] In the United States, the overall prevalence is 22 per 100,000 population, with HTLV-2 more common than HTLV-1. Data collection performed from 2000 to 2009 among US blood donors has shown a general decline since the 1990s.[6]
Symptoms
Human T- leukemia, type 2 (HTLV-2) generally causes no signs or symptoms. Although HTLV-2 has not been definitively linked with any specific health problems, scientists suspect that some affected people may later develop neurological problems such as:[7][6]
Sensory neuropathies (conditions that affect the nerves that provide feeling)
Figure 1. Mycosis fungoides, a skin disease showing nodules and plaques composed of lymphocytes spread across the skin, has been associated with HTLV-II infection[5]
Although evidence is limited, there may also be a link between HTLV-2 and chronic lung infections (i.e. pneumonia and bronchitis), asthma and dermatitis.[8]
Due to there being no cure for HTLV II the prevention is focused on early detection and preventing the spread of HTLV-2 to others. blood donors, promoting safe sex and discouraging needle sharing can decrease the number of new infections. Mother-to-child transmission can be reduced by screening pregnant women so infected mothers can avoid breastfeeding.[8]
Prognosis
The long-term outlook for most people infected with HTLV-2 is good. Infection with HTLV-2 is lifelong, but 95% of affected people have no signs or symptoms of the condition. Although, HTLV-2-related health problems tend to be significantly milder than those associated with HTLV1.[8]
^ abcde"Human T-cell leukemia virus type 2". US Department of Health and Human Services | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. Retrieved 2019-02-22. This article incorporates text from this source, which is in the public domain.
^Kalyanaraman VS, Sarngadharan MG, Robert-Guroff M, Miyoshi I, Golde D, Gallo RC (November 1982). "A new subtype of human T-cell leukemia virus (HTLV-II) associated with a T-cell variant of hairy cell leukemia". Science. 218 (4572): 571–3. Bibcode:1982Sci...218..571K. doi:10.1126/science.6981847. PMID6981847.
