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Human pathogenic retroviruses (HTLV) belong to the genus Deltaretrovirus, in addition to the genus Lentivirus (which includes HIV). They were the first retroviruses discovered, which are referred to as oncoviruses due to their proven oncogenic potential.
The HTLV-1 and HTLV-2 virus types are very similar to each other, show homology in nucleotide sequences for more than 60%, and are difficult to distinguish using standard tests. The target cells for HTLV-1 are CD4 + lymphocytes, and for HTLV-2 – CD8 + lymphocytes, but other cells may also be infected. Unlike HIV, there is no known cellular receptor for HTLV. Both HTLV-1 and HTLV-2 are capable of neoplastic transformation of target cells, although they do not contain specific oncogenes.
Epidemiology retrowirusów
It is estimated that 1-2 million people worldwide are carriers of HTLV-15 and HTLV-25. HTLV-1 infection is endemic in southwest Japan (up to 30% of infected people), the Caribbean (up to 5%), South America and some areas of Africa, while HTLV-2 is most commonly found among the Native Americans.
In Europe and the United States, less than 0,1% of the population is infected (in the US 0,01-0,03%). More often the virus is detected in women and black people, the percentage of infected increases with age. Only 1-5% of people infected with retroviruses develop clinical symptoms related to the presence of the virus, others remain asymptomatic carriers for the rest of their lives.
HTLV-1 transmission can occur via the following routes:
- during sexual contact (usually from a man to a woman; there is no increased risk of transmission in case of homosexual contact);
- by transfusion of blood or blood products (risk after transfusion of an infected person’s blood is 40-60%, seroconversion occurs 7-8 weeks after the transfusion);
- by sharing needles and syringes among injecting drug users;
- vertically, especially during breastfeeding (the risk of vertical transmission of the virus by an infected mother is estimated at 20%).
The major route of transmission of HTLV-2 is through drug addiction infection via contaminated intravenous injection equipment. The infectious material is:
- blood,
- seed,
- breast milk containing HTLV-infected T lymphocytes (infection does not occur through free viral particles).
The mode of infection is thus similar to HIV transmission, but the risk is lower because HTLV – unlike HIV – cannot be transmitted through cell-free material. The incubation period for HTLV diseases is shorter in the case of transmission by blood transfusion and in immunocompromised individuals. Acute HTLV infection is asymptomatic and is very rarely diagnosed on the basis of seroconversion.
In adults, HTLV-1 infection may develop after many years proliferative diseases malignant and chronic neurological degenerative syndromes. The etiological relationship of HTLV-1 with the following disease entities has been proven:
- adult T-cell lymphoma / leukemia (ATLL);
- myelopathy / tropical spastic paralysis (HTLV – asso ciated myelopathy – HAM / tropical spastic paraparesis – TSP);
- chronic inflammatory symptoms of various organs (uveitis, dermatitis, arthritis, interstitial pneumonia).
Moreover, a link between HTLV-1 infection and skin lymphomas (Sezary’s syndrome, mycosis fungoides) and z autoimmune diseases (e.g. Sjögren’s syndrome).
HTLV-2 was first isolated from a patient with hairy cell leukemia, but the role of the virus in hairy cell leukemia has not been definitively confirmed. HTLV-2 may be associated with lymphoproliferative diseases and neurological disorders such as spastic paralysis / myelopathy. Some authors question the role of HTLV-2 as the etiological factor of any disease.
Although no effective cure has been found, antiretroviral treatment allows patients to live up to 40 years. Treatment is most effective in the first phase of AIDS. Adequate diet and physical activity are important in antiretroviral treatment. Patients should consume a large amount of nutrients, including fruit and vegetables. Ideally, they should avoid eating raw eggs or unpasteurized milk to prevent salmonella, which is very severe in AIDS patients.
There are five antiretroviral preparations on the market, including: zidovudine, stavudine, lamiduvine and zalcitabine. HIV research is still ongoing, so you may suspect that over time, the number of drugs available will continue to increase.
Taking into account the number of lymphocytes, treatment is as follows:
- 500 lymphocytes or less – zidovudine and other antiretroviral agents are being implemented
- 200 lymphocytes or less (also taken in the presence of oral candidiasis and other symptoms of impaired immunity) – treatment (or prevention in the absence of disease symptoms) infection with Pneumocystis carinii,
- 70 lymphocytes or less – treatment (or prevention in the absence of disease symptoms) of Mycobacferium avium.
Source: J. Cianciara, J. Juszczyk, Infectious and parasitic diseases; Czelej Publishing House