Hi everyone, welcome to the LactFact podcast, which highlights recent, clinically relevant research, policy statements, and protocols that you, as a practicing lactation professional, should know about. I am your host, Dr Anne Eglash. I am a board-certified family physician and breastfeeding and lactation medicine specialist at the University of Wisconsin School of Medicine and Public Health.

This podcast is written and produced by the nonprofit organization IABLE, which is the Institute for the Advancement of Breastfeeding and Lactation Education. There are no commercial funders for this podcast series.

Hi everyone,
In a few days it will be 2026, and I wish you all happy and healthy new year, and thanks for listening to the IABLE podcasts.

Today I am discussing a study regarding HTLV-1 virus, also known as the human T lymphotropic virus type 1. I am going to stick with the term HTLV-1.

First let’s review some background.

Pregnant women in the United States and in other countries are routinely screened for certain infectious diseases such as rubella, syphilis, HIV, Hepatitis B and C, and group B strep.

HTLV 1 and 2 are viruses identified 40 years ago, for which we have no treatment or vaccine to prevent infection. People infected with HTLV 1 have a 2-6% risk of adult T cell leukemia or lymphoma and 2-3% can develop tropical spastic paraparesis. HTLV 2 is a much less virulent cousin of HTLV 1, although people infected with it have a higher risk of cancer.

HTLV 1 is transmitted horizontally through sexual intercourse and infected blood. It can also be transmitted vertically. Breastfeeding is the primary means of mother to child transmission, with an estimated 20% of breastfed newborns contracting HTLV 1 from their infected birth parent. This is because the virus prefers to live in immune cells which are of course abundant in breastmilk, and infection involves the transmission of cells that contain the virus. The virus does not live extracellularly, which is probably why there is less transmission transplacentally or during the birthing process as compared to breastfeeding.

The risk of transmission is higher with a higher maternal viral load and a longer duration of breastfeeding.

It is estimated that 5 to 20 million people worldwide have HTLV -1 infection, with less than 1% of people in North America being infected. Approximately 1/3 of the population with HTLV 1 live in parts of Japan, Africa, South America, Australia, Iran, and the Caribbean.

Because The United States is a melting pot with people who originate from every country worldwide, there continues to be a low level risk of HTLV -1 infection. The American Red Cross , which tests for HTLV 1 &2, estimates that 2 in 100,000 donations are positive.

Screening for HTLV-1 has been implemented in many countries where there is a high prevalence such as in Japan. A national antenatal screening program in Japan reduced maternal child transmission from 20% to 2.5%. Even in the UK where prevalence is low, screening during pregnancy has been found to be cost effective.

In the United States pregnant women are not routinely screened for HTLV, although it would certainly be reasonable to screen individuals at risk including those who have used intravenous drugs, and in people who were born in countries and regions where HTLV-1 is endemic.

The article I want to discuss today is a survey done among OB providers in France to measure their knowledge regarding the contraindication of breastfeeding with HTLV-1 infection, and it’s endemic geographic regions. HTLV -1 prevalence is higher per capita in France compared to the USA because of being closer to Africa and migration from former French colonies where HTLV-1 rates are endemic.

The survey was conducted in 2022, and sent to thousands of obstetricians gynecologists ,midwives, and general practitioners.

They received 936 completed surveys, 75% were midwives, 22% were OB/Gyns, and 3% were general practitioners.

They found that only 27.5% of the respondents thought HTLV-1 infection was a contraindication to breastfeeding. Those who were more likely to be knowledgeable worked with a high percentage of migrants or in an endemic French overseas territory such as W Indies or Guiana. That said only 32% of participants working in those regions were aware of HTLV one infection being a contraindication to breastfeeding.

When asked about screening pregnant women for HTLV one infection 6.6% said that they often test for it, 14.5% sometimes tested and 79% never tested. Those with specific training in OB infectious disease were much more likely to screen for HTLV-1, in addition to those who practiced with a significant percent of immigrants or worked in endemic overseas territories. At least 75% of the respondents did not know which countries were endemic with HTLV one infection.

After this survey was published French infectious diseases society drafted screening guidelines to include screening for HTLV one for all women of childbearing age from South America, the Caribbean, and sub-Saharan Africa.

I think this is a lesson for the USA. I suspect, without evidence, that we need to increase awareness of the risk factors for HTLV-1, and screen high risk populations, especially during pregnancy, to prevent spread of HTLV-1 during lactation.

There is evidence that limiting breastfeeding to 3 months does not increase the risk of HTLV-1 transmission because of the existence of HTLV-1 antibodies transmitted trans-placentally, which hang around in the newborn for a few months. In addition, research in Japan has preliminarily shown that freezing and thawing breastmilk to 20 ° C for 24 hours markedly decreases the risk of HTLV-1 transmission because the freezing process seems to kill the virus. There is insufficient evidence that flash pasteurization or holder pasteurization of infected milk eliminates the virus.

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