In a world first, researchers from The University of Western Australia have taken the first step towards understanding whether it may be possible for breastfeeding mothers to naturally vaccinate their babies against malaria – one of the world’s deadliest contagious diseases.
The study was led by Professor Valerie Verhasselt, from UWA’s School of Molecular Sciences, and Dr Thomas Egwang from Uganda, with UWA’s Dr Lieke van den Elsen as first author. Professor Verhasselt said the research introduced a new concept that could be tested to prevent the spread of malaria.
“More than 200 million cases of malaria are reported each year around the world, with the majority in Africa,” Professor Verhasselt said.
“Infants aged under five years account for two-thirds of all malaria deaths, highlighting the need for early and efficient prevention of malaria infection.”
She said breastfeeding was the most efficient way to prevent childhood disease and death related to respiratory and gastro-intestinal infectious disease.
“Before this study, there was conflicting evidence on whether breastfeeding could prevent malaria and we wanted to find a way to ensure malaria prevention through breastfeeding,” she said.
“Based on our longstanding expertise in the field of allergy prevention through breastfeeding, we propose the original hypothesis that the presence of malaria antigen (proteins) in breastmilk stimulates anti-malarial immune defence and reduces malaria risk in breastfed infants. This would be a way to naturally vaccinate infants.”
The researchers investigated whether two proteins from malaria parasites were detectable in the breastmilk of mothers from Uganda, a country where malaria is widespread.
The research, published today in JAMA Pediatrics, shows for the first time that 15 per cent of breastmilk samples from mothers who carry the malaria parasites without symptoms, contain malaria antigens in their breastmilk.
They propose these mothers may be the ones able to naturally vaccinate their child against malaria as their breastmilk would contain malaria proteins together with additional factors specifically adapted to the babies’ immune system.
She said breastfeeding was the most efficient way to prevent childhood disease and death related to respiratory and gastro-intestinal infectious disease.
Professor Verhasselt, who is also the Larssen-Rosenquist Chair in Human Lactology at UWA, said the next step was to carry out clinical trials to assess immunological outcomes and malaria risk in infants exposed to one or multiple malaria antigens through breastmilk.
“We could then propose to vaccinate breastfeeding mothers to increase levels of malaria antigen in breastmilk, ensuring vaccination and long-term protected of their child,” she said.
More than 200 million cases of malaria occur yearly, with most in Africa, where infants younger than 5 years account for two-thirds of all malaria deaths.1 This highlights the need for successful prevention of malaria infection, especially in early life. Breastfeeding is the most efficient way to prevent child morbidity and mortality attributable to respiratory and gastrointestinal tract infectious diseases.2
In contrast, there is conflicting evidence on malaria prevention by breastfeeding.3–5 Mouse and human data have shown that the presence of foreign antigens in breast milk, such as allergens or viral antigens, could elicit strong immune responses in offspring who are breastfed.6
Therefore, we propose what is to our knowledge an original hypothesis: the presence of malaria antigen in breast milk stimulates antimalarial immune defenses and reduces malaria risk in infants who are breastfed. Here, as a critical first step to address this hypothesis, we investigated whether Plasmodium falciparum histidine-rich protein 2 (pHRP-2) and lactate dehydrogenase (pLDH) are detectable in the breast milk of mothers from Uganda, a country with endemic malaria.1Methods
This study included mothers who were lactating and who visited our malaria clinic at St Anne Health Center III, Katakwi District, northeastern Uganda, during the high or low malaria-transmission seasons. Five-milliliter samples of breast milk and fingerprick blood samples were collected after the mothers provided informed consent. Ethical approval for the study was provided by the Uganda National Council for Science and Technology.
The blood samples were used immediately to detect asymptomatic malaria by an ultrasensitive P falciparum HRP-2–based rapid diagnostic test (uRDT) (Alere Malaria Ag P.f [Standard Diagnostics Inc]). The presence of malaria antigens in breast milk samples was investigated by P falciparum–specific pHRP-2 and pLDH enzyme-linked immunosorbent assays (Quantimal CELISA [Cellabs]), with protocol adaptation (detection levels were 1.2 pg/mL and 4.8 units/mL, respectively).
Data analyses were performed with Prism version 6 (GraphPad Software). We used 2-sided Fisher exact tests to address differences between groups, and P values less than .05 were considered significant. Data collection and analysis occurred from March 2018 to December 2018.Results
A total of 123 mothers who were lactating visited the malaria clinic during the low malaria-transmission season; an additional 201 visited during the high transmission season. The overall mean [SD] age, body mass index (calculated as weight in kilograms divided by height in meters squared), and lactation duration of the mothers analyzed in this study were 26.2 [6.8] years, 23.6 [2.8], and 12.3 [5.5] months, respectively.
None of the mothers had clinical malaria. When malaria transmission was low and high, 14 of 123 women (11.4%) and 74 of 201 women (36.8%), respectively, harbored asymptomatic malaria (P < .001). Among the 88 breast milk samples from mothers with asymptomatic malaria, 7 had detectable pHRP-2 (7.9%) with a median (interquartile range) level of 45.0 (2.0-180.2) pg/mL, and 10 had detectable pLDH (11.3%) with median (interquartile range) values of 6.6 (5.6-9.9) arbitrary units/mL (Figure 1).
Overall, 14 breast milk samples (15.9%) were positive for either pLDH or pHRP-2, and 3 (3.4%) were positive for both pLDH and pHRP-2. Forty-four milk samples from mothers without malaria were used as control samples, and none of these showed detectable pHRP-2 or pLDH antigens (Figure 1).
To address whether the detection of malaria antigens in breast milk depended on the density of P falciparum parasites in mothers’ blood circulation, we categorized the intensity of the test bands of the uRDT readout for 74 malaria-positive blood samples as faint, moderate, or intense, as a proxy measure of parasite density. In the faint category, 1 of 28 samples was positive, with a value of 1.52 pg/mL; in the moderate category, 1 of 18 samples was positive, with a value of 5.4 pg/mL; and in the intense category, 4 of 28 samples were positive, with a median (interquartile range) value of 112.0 (12.6-212.3) pg/mL (Figure 2). Further statistical analysis could not be performed because of the limited size sample. These preliminary data suggest that percentage of breast milk samples positive for pHRP-2 and the concentration of pHRP-2 in breast milk increased with the intensity of test bands.
