Sky-high rates of rare retrovirus in central Australia

A study of remote Aboriginal communities recorded the highest infection rate of human T-cell leukaemia virus, type 1 in the world.

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More than one-third of people in remote central Australian Indigenous communities are living with a rare retroviral infection that may cause leukaemia later in life. 

With no public health strategy in place, researchers are calling for strengthened disease education programs. 

Human T-cell leukemia virus, type 1 (HTLV-1) is endemic in Aboriginal populations in central Australia. 

HTLV-1 primarily affects T-cells. 

While about 95% of infected people will remain asymptomatic, some will later develop adult T-cell leukaemia or HTLV-1-associated myelopathy or tropical spastic paraparesis. 

High levels of peripheral blood leukocytes are also associated with an increased risk of chronic lung disease in Aboriginal Australians. 

Transmission is understood to occur mainly through blood contact, unprotected sex and breast feeding, and there is no current cure or treatment. 

To date, the actual prevalence of HTLV-1 has not been clear, but now the first large-scale community study looking at infection rates in central Australia has been published in PLOS Neglected Tropical Diseases.

Researchers tested 720 people from seven remote communities south-west of Alice Springs for HTLV-1. 

They found a prevalence of 37% in people over the age of 15, the highest community prevalence recorded worldwide. 

The proportion of people who tested positive increased with age, reaching almost 50% prevalence in adults older than 45. 

“The sharp increase in the prevalence of a chronic infection around adolescence suggests that sexual contact may be playing an important role in transmission, and this is considered to be the explanation for the age-prevalence relationship in other HTLV-1 endemic areas,” the authors wrote. 

The role of sex in transmission is inferred based on international studies that found associations between HTLV-1 infections and higher numbers of sexual partners, the presence of genital lesions and a history of previous sexually transmitted infections.

“Although condomless sexual intercourse is considered to be the major mode of transmission worldwide, sharing devices used for self-flagellation in a religious context was associated with HTLV-1 transmission in a recent report from the UK, which suggests that predisposing factors may vary in different populations,” the researchers said. 

“Further studies by Aboriginal researchers are needed to more clearly define the risk factors for HTLV-1 transmission in this population.” 

Children had the lowest rate of infection, despite the fact that breast feeding is also a suspected mode of transmission. 

“Despite the low prevalence, acquisition of HTLV-1 infection in early life is clinically very important because of its strong association with [adult T cell leukaemia/lymphoma], a fatal haematological malignancy that has been reported at Alice Springs Hospital,” the authors said. 

No public health strategy to control the disease in Indigenous communities has ever been formulated, let alone implemented. 

“Results of the present study argue for the implementation of a coordinated program to inform Aboriginal Australians of the risks posed by HTLV-1 infection and to reduce the risk of viral transmission in this population,” the researchers wrote.

PLOS Neglected Tropical Diseases 2021, online 8 December