Can Virus Be Transferred to Baby Thru Breastmilk
Breast feeding and the risks of viral transmission
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Specialised epidermal secretions developed as nutritious and bacteriostatic factors some 120 million years ago; milk product has proved a crucial factor to mammalian survival in a wide range of habitats. Milk composition differs considerably between phyla, inside species, and with time in an private lactating mother. The neonatal flow claims the greatest infectious toll in mammals so that from an evolutionary standpoint there must be a balance in favour of producing and consuming milk without increasing susceptibility to infection. Competitive interaction with viruses, leaner, and protozoans has resulted in the development of unique characteristics within breast epithelial cells. Unlike equivalent cells in sweat or salivary glands, they secrete nutritive molecules, antibody substances, growth factors, inflammatory cytokines, and chemokines while regulating a physiological recruitment of lymphoid and myeloid cells from the apportionment into the milk. Milk therefore has functions other than nutrition; milk is a complex mixture of cells, membranes, and molecules. Epidemiological data from the HIV pandemic have highlighted our lack of knowledge about this secretion.
It was established in the 1960s that milk was a significant source of infection to mouse pups for Moloney leukaemia virus, sarcoma virus, and mammary tumour virus: other species bear witness similar patterns of manual of lentiviruses.ane In man the RNA retroviruses including HIV-one, HTLV-ane, and HTLV-2 are all transmitted by this route.ii It has been recorded that HIV-two is non transmitted by breast milk, but it is likely that there is a relatively lower hazard in this less virulent retrovirus equally well as fewer information to assess infectivity. Cytomegalovirus is possibly the near commonly detectable virus in milk: it is thought that reactivation of virally infected breast epithelial cells in early lactation promotes the shedding of infectious complimentary virus particles.iii Rubella, herpes simplex, and rarely hepatitis B can be passed on to the infant too if mothers have an active infection.4 EBV and HHV6 may be found in man milk, but big serological studies suggest that they rarely infect the breast fed neonate.5 Hepatitis C RNA has non been detected in milk in one series, and the infection charge per unit by this road is probably low unless the maternal viral load is high.six-viii
The challenge to clinicians is therefore to determine the run a risk to any particular babe of milk borne infection: can i estimate the hit charge per unit of these organisms in milk? Reports from various populations prove a range of infectious rates for cytomegalovirus (xl–76%),9 ,10 rubella (25–fifty%),4 HTLV-1 (80%),11 and HIV-1 (5–66%).12-14 A meta-analysis approach estimated an boosted chance of xiv% (95% conviction interval seven–22%) of mother to kid HIV infection conferred past breast feeding13; an increased adventure of 26% (95% CI 13–39%) for incident cases.14 These broad ranges of hit rates indicate a complication in the underlying process of manual which merit clarification. Given the volume of milk consumed daily by an infant it is surprising that milk is not more infectious, and there are conspicuously strong protective factors at work. At present there are insufficient information to rank known risk factors most probable to increase maternal infectivity or infant susceptibility (table one), let lone disease severity. Milk constituents vary considerably between mothers, and over time in a single woman, rendering many objective measures impractical. Milk composition is influenced by gestation, treatment with steroids, or psychological stress: the interactions between these events and the roles of breast epidermal cells remain unclear.
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Table 1
Factors promoting or inhibiting transmission of virus past breast feeding
Epidemiological work with HTLV-1 and HIV has provided a range of information on the risk of acquiring infection at different stages of lactation.11 ,14-16 Claims have been fabricated for lower infection rates early on in lactation, for instance, merely many of these studies did not make up one's mind whether mothers breast fed exclusively, a gene which may be critical to viral transmission. A recent study in a South African population suggested that mixed formula and breast feeding was more than likely to promote HIV-i transmission than exclusive breast feeding, and for this reason studies of sectional chest feeding are being carried in Durban.13 This work is critical to infants in the developing world, for whom exclusive breast feeding may often be the safest option, particularly if clean water is not available. These bug revolve effectually our lack of precise knowledge every bit to the mechanisms whereby virus infects the breast feeding infant. Retroviruses may infect the mammary epithelial prison cell antenatally; they are also found free in solution and within milk monocytes which comprise most 50% of the cells in healthy milk.17 (These cells normally protect the glandular tissues as phagocytes and by providing professional local antigen presentation; they may have similar functions in the neonatal gut.18 ,19) Maternal cells may therefore have the potential to bear viruses from female parent's circulation or lymphoid tissues into the neonatal gut. Studies of HIV strains add together further complication: most developed HIV infections develop from macrophage-tropic strains of the virus which utilise the chemokine receptor CCR5. However CCR5 chemokine receptor heterozygosity does not protect infants against infection past breast feeding (although the mutation Δ32 in the CCR5 receptor may protect confronting infection in utero).xx Mayhap orally delivered virus enters the babe via cells which exercise not bear these receptors: such portals could include enterocytes and M cells in the infant gut, which in animal models take up gratuitous virus from the intestinal lumen. The precise role of milk cells in viral infection and the range of viral portals of entry have therefore to be elucidated.21
Clinical mastitis and breast abscesses increment the charge per unit of vertical viral transmission: this aspect of maternal health tends to reflect the adequacy of support and information provided to breast feeding mothers, every bit these disorders are oft preventable.22 Subclinical mastitis merits conscientious consideration: this term describes bacteriologically civilization positive milk without clinical symptoms: there is an associated increase in milk sodium concentration, cell counts, inflammatory cytokines, enzymes, and reduced milk production.23 Samples from several communities suggest rates of twenty–33% of this entity which may promote infection of the infant with HIV (at that place are no data relating to other viruses).24 Mastitis causes immune activation in the breast promoting viral manual by the production of activated cells (dendritic cells in detail) and mediators known to induce viral replication in breast epithelium and activate infant enterocytes. The aforementioned may be truthful of subclinical mastitis. The comparative significance of these observations has to be determined, but active management of clinical mastitis offers mothers, midwives, and doctors an opportunity to reduce the risks of vertical viral transmission. Enhancing maternal nutrition (peradventure with trace elements, vitamins, and antioxidants) or enhancing genetic resistance to reduce subclinical or clinical mastitis through diet or medications volition diminish the risks of milk borne viral transmission.25
Can breast milk be cleared of viruses? In the case of retroviruses, might milk be washed as may semen in order to remove active virus? Although ane might conceivably remove cell associated virus by filtering, gratuitous viral particles are difficult to eliminate. Pasteurisation to 62.5°C volition destroy infectious viral particles, merely this also alters milk composition to a meaning degree, and in practical terms is often limited past the requirement for scrupulous hygiene.26 ,27 Protective mechanisms of the innate and cellular immune system at work during lactation could potentially be exploited by vaccination. Such approaches need to be extensively tested in an advisable animal model: in dairy cows protection against bacterial infection has been enhanced using this approach. Most promising of all for brusque term approaches to retroviruses are therapeutic studies showing that a single dose of nevirapine, a not-nucleoside contrary transcriptase inhibitor, tin clear milk of virus and then permit rubber early breast feeding.28 Provision of cut toll or free nevirapine by not-governmental organisations and pharmaceutical companies to many African countries has fabricated this a readily available handling. Even so, widespread employ of a unmarried agent in this setting will encourage the evolution of resistance and may be associated with rebound viraemia when the agent is stopped, with a potential increase in maternal infectivity and as yet undetermined effects on maternal health.21
Paediatricians will accept to dedicate greater effort to estimating the risks posed past vertical viral transmission by breast feeding. Milk banks with pasteurised milk and wet nursing practices may offering local solutions, but will crave vigilant supervision. Maybe the monitoring of milk prison cell counts or sodium concentrations in addition to bacteriological screening should be studied as a potential method of quality command for such sources. At a global level, in that location must exist a continued delivery to supporting breast feeding as the safest class of babe nutrition for those mothers who do not take an active viral infection: the situation is rarely 1 of tainted breast milk, but t'aint enough.
Acknowledgments
We should like to thank Dr Donald Bentley, Professor Angus Nicoll, and Professor Felicity Cruel for their helpful comments during the preparation of this review.
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