Overview
HTLV-1 can be transmitted vertically through breastfeeding and possibly during pregnancy or at birth. Diagnosis in pregnant people may enable them to take measures to reduce transmission. However, there are many uncertainties relating to evidence, and in personal values and preferences related to a HTLV-1 diagnosis. There are also many uncertainties and risks in relation to not breastfeeding.
Testing
Testing is requested on a serum sample. Local laboratories will perform an initial HTLV-1 screening antibody test, which is then sent to a reference laboratory for confirmation. Confirmation is usually performed with Western Blot. Ideally a PCR test is also used to aid confirmation, however this is as of March 2025 not currently funded by the Medicare Benefits Schedule.
The result will be reported as positive, negative or indeterminant. Indeterminant results can usually be resolved with repeat testing after a 1-month interval.
When to Test
At the first antenatal visit, determine whether the pregnant person’s HTLV-1 status is known. For pregnant people known to be living with HTLV-1 infection refer to the recommendations section below.
For pregnant people of unknown status, or where their previous test was HTLV-1 negative, a discussion about the risks and benefits of HTLV-1 testing should begin as soon as possible in the pregnancy. This is to try and ensure sufficient time to receive their test results and if needed make a shared decision about feeding their baby and discuss breastfeeding duration.
Discussion about testing should be deferred if the practitioner does not have sufficient knowledge to adequately inform the person of the implications of testing. Ideally, testing will occur early in pregnancy to allow the person time to consider feeding options prior to the baby’s birth. However, as the greatest risk of transmission is associated with breastfeeding after 6 months of age there is still potential benefit to testing at any stage of pregnancy and into the breastfeeding period.
What is Shared Decision Making?
Shared decision making is a consultation process where a clinician and person jointly participate in making a health decision, having discussed the options and their benefits and harms, and having considered the patient’s values, preferences and circumstances. Shared decision making is especially valuable when there is uncertainty as to which option is superior, when each option has different inherent benefits and harms, or when the decision is likely to be strongly influenced by patients’ preferences and values.
Documentation of shared decision making is also important so that other services do not repeat the process, particularly for pregnant people who access primary care at several clinics, or who attend specialist antenatal clinics throughout pregnancy.
Additional information on shared decision making can be found here: Shared decision making | Australian Commission on Safety and Quality in Health Care
Shared Decision Making and Pregnancy
Encouraging open conversations and trust with pregnant people and their families is essential to minimise stigma and support information sharing.
A positive result can have negative social and emotional wellbeing impacts including stress and anxiety. However, with adequate support and counselling it also allows the pregnant person to make an informed decision about breastfeeding when it suits them.
It is never appropriate for a health care provider to inform a pregnant or breastfeeding person living with HTLV-1 that they are not able to breastfeed their infant. Decisions regarding method of feeding require informed discussion between the person and their care team, with consideration of the risks and benefits of breast feeding given the pregnant or breastfeeding person’s situation.
Suitable decision-making aids should be used to guide a discussion between the pregnant person and their care givers. People should understand the implications of a positive HTLV-1 result for them and their babies and be supported to consider the impact of their individual values and preferences before undergoing testing. This includes the following:
- On average overall about 1 in 5 pregnant persons will pass HTLV-1 on to their babies during pregnancy, birth or breastfeeding, with breastfeeding accounting for most transmission.
- If breastfeeding is completely avoided there is still a risk of about 1 in 20 of passing on HTLV-1.
- There is uncertainty about the level of risk for short-term limited breast feeding, the following estimates are mainly based on Japanese data (Table 1).
- Breastfeeding for less than 3-months does not increase the risk of transmission above the residual 1 in 20 risk (Table 1).
- Breastfeeding beyond 6-months greatly increases the risk of transmission to about 1 in 5 (Table 1).
Table 1: Breastfeeding scenarios and risk of transmission
| Scenario | Risk of Transmission Mother to Child | Degree of Certainty |
|---|---|---|
| Baseline risk of transmission (birth, all events) | 1/20 | High certainty |
| Breastfeeding (0-3 months) | 1/20 | Low certainty |
| Breastfeeding (3-6 months) | 1/10 | Low certainty |
| Breastfeeding (>6 months) | 1/5 | High certainty |
- People with HTLV-1 and a higher proviral load are most at risk of transmitting HTLV-1 to their babies and may be more important to limit the duration of breastfeeding to 3-months or less. A proviral load of more than 0.5% tripled the rate of transmission in one study. It is not known whether there is a viral load threshold below which transmission does not occur.
- Breastfeeding has many health, social and emotional benefits for the person and their baby. For breastfeeding parents this includes supporting a healthy weight and reducing the risk of a range of diseases including diabetes, breast cancer, ovarian cancer, endometrial cancer, high blood pressure and cardiovascular disease. For babies this includes healthy growth and development and reducing risk of infections and conditions such as gastroenteritis, respiratory infections, ear infections, type 1 and 2 diabetes, obesity and some cancers. In communities with a high disease burden, and high levels of food insecurity and poverty, the benefits and risks of breastfeeding need to be carefully considered based on the person’s personal circumstances.
- Breastfeeding is most important in the first 6 months of life although there is clear evidence of the benefit of breast feeding for two years and beyond, which is the WHO recommendation.
- Commercial milk formula (CMF) feeding is expensive and is associated with safety risks, such as serious infections, if appropriate preparation and sterilisation can’t be achieved. Safely using CMF may be more difficult for parents living with poverty, energy insecurity, and in transient, overcrowded or poorly maintained housing.
- Given that social norms and accepted best practice promote breastfeeding, parents who choose not to breastfeed, or to limit breastfeeding, irrespective of HTLV-1 status, may experience stigma related to their choice of infant feeding.
- Becoming infected with HTLV-1 as an infant may affect their health later in life. Based on information from overseas HTLV-1 causes ATLL in about 1 in 20 people, and HAM/TSP in about 1 in 50. HTLV-1 is also associated with some other diseases and with an overall reduced life expectancy. For more information refer to Clinical Presentation.
- If a person is diagnosed with HTLV-1 in pregnancy, there are significant implications for their own health and there are no specific treatments available for the infection. For more information refer to Management and Care.
Postnatal Care
After the birth of their baby, people with a diagnosis of HTLV-1 should be offered further support to implement the feeding method that they have chosen. A specific review appointment may be required, for example when the infant is 3 or 6 months of age, particularly if a limited duration of breastfeeding is intended.
Recommendations
All people who are giving birth to an Aboriginal baby, are living in or were born in high prevalence communities for HTLV-1 should be provided with information about HTLV-1. This should include the availability of HTLV-1 testing and the implications of a positive and negative test for their own and their baby’s health and wellbeing, to enable them to make an informed shared decision about testing for HTLV-1. This discussion should occur as soon as possible, with a person knowledgeable about HTLV-1.
HTLV-1 testing should never be included in a predefined antenatal care test set.
All pregnant people diagnosed with HTLV-1 should be offered a pro-viral load test during each pregnancy to help ascertain their individual risk of transmission. As of March 2025, this test is not funded by Medicare and clinicians should seek local advice from their laboratory or an expert in HTLV-1 about availability and costs.
All pregnant people diagnosed with HTLV-1 should be provided with support to make an individual assessment of the risks and benefits of breastfeeding for both the mother and the infant. This includes evaluating whether to breast or formula feed, the duration of breastfeeding, what information and resources are required for safe infant feeding.
Mixed feeding (breastfeeding combined with formula feeding) is not recommended for mothers with HTLV-1, as it may increase the risk of transmission to the infant. Although specific studies on HTLV-1 are lacking, evidence from HIV research indicates that mixed feeding increases the risk of vertical transmission.
All pregnant people with HTLV-1, regardless of proviral load, should be provided with lactation and feeding advice and resources to provide CMF to their baby safely and reliably if they choose to use CMF.
No recommendation is made about the mode of delivery.
References
- Itabashi K, Miyazawa T. Mother-to-child transmission of human T-cell leukemia virus type 1: mechanisms and nutritional strategies for prevention. Cancers. 2021;13(16):4100.
- Boostani R, Sadeghi R, Sabouri A, Ghabeli-Juibary A. Human T-lymphotropic virus type I and breastfeeding; systematic review and meta-analysis of the literature. Iranian journal of neurology. 2018;17(4):174.
- Hisada M, Maloney EM, Sawada T, Miley WJ, Palmer P, Hanchard B, et al. Virus markers associated with vertical transmission of human T lymphotropic virus type 1 in Jamaica. Clinical infectious diseases. 2002;34(12):1551-7.
- Fowler F, Einsiedel L. A qualitative study exploring perceptions to the human T cell leukaemia virus type 1 in central Australia: Barriers to preventing transmission in a remote aboriginal population. Frontiers in Medicine. 2022;9:845594.
