A vertically transmitted infection is an infection caused by pathogenic bacteria or viruses that use mother-to-child transmission, that is, transmission directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth. It can occur when the mother has a pre-existing disease or becomes infected during pregnancy. Nutritional deficiencies may exacerbate the risks of perinatal infections. Vertical transmission is important for the mathematical modelling of infectious diseases, especially for diseases of animals with large litter sizes, as it causes a wave of new infectious individuals.
Types of infections
Bacteria, viruses, and other organisms are able to be passed from mother to child. Several vertically transmitted infections are included in the TORCH complex:
T – toxoplasmosis from Toxoplasma gondii
O – other infections (see below) R – rubella C – cytomegalovirus H – herpes simplex virus-2 or neonatal herpes simplex
Other infections include: Parvovirus B19 Coxsackievirus Chickenpox (caused by varicella zoster virus) Chlamydia HIV
Human T-lymphotropic virus
Syphilis
Zika fever, caused by Zika virus, can cause microcephaly and other brain defects in the child. COVID-19 in pregnancy is associated with an increased risk of stillbirth with an odds ratio of approximately 2.
Hepatitis B may also be classified as a vertically transmitted infection. The hepatitis B virus is large and does not cross the placenta. Hence, it cannot infect the fetus unless breaks in the maternal-fetal barrier have occurred, but such breaks can occur in bleeding during childbirth or amniocentesis.
The TORCH complex was originally considered to consist of the four conditions mentioned above, with the "TO" referring to Toxoplasma. The four-term form is still used in many modern references, and the capitalization "ToRCH" is sometimes used in these contexts. The acronym has also been listed as TORCHES, for TOxoplasmosis, Rubella, Cytomegalovirus, HErpes simplex, and Syphilis.
A further expansion of this acronym, CHEAPTORCHES, was proposed by Ford-Jones and Kellner in 1995: C – chickenpox and shingles H – hepatitis, C (D), E E – enteroviruses A – AIDS (HIV infection) P – parvovirus B19 (produces hydrops fetalis secondary to aplastic anemia) T – toxoplasmosis O – other (group B streptococci, Listeria, Candida, and Lyme disease) R – rubella C – cytomegalovirus H – herpes simplex E – everything else sexually transmitted (gonorrhea, Chlamydia infection, Ureaplasma urealyticum, and human papillomavirus) S – Syphilis
Signs and symptoms
The signs and symptoms of a vertically transmitted infection depend on the individual pathogen. In the mother, it may cause subtle signs such as an influenza-like illness, or possibly no symptoms at all. In such cases, the effects may be seen first at birth.
Symptoms of a vertically transmitted infection may include fever and flu-like symptoms. The newborn is often small for gestational age. A petechial rash on the skin may be present, with small reddish or purplish spots due to bleeding from capillaries under the skin. An enlarged liver and spleen (hepatosplenomegaly) is common, as is jaundice. However, jaundice is less common in hepatitis B because a newborn's immune system is not developed well enough to mount a response against liver cells, as would normally be the cause of jaundice in an older child or adult. Hearing impairment, eye problems, mental retardation, autism, and death can be caused by vertically transmitted infections.
The genetic conditions of Aicardi-Goutieres syndrome are possibly present in a similar manner.
Causal routes
The main routes of transmission of vertically transmitted infections are across the placenta (transplacental) and across the female reproductive tract during childbirth. Transmission is also possible by breaks in the maternal-fetal barrier such by amniocentesis or major trauma.
Transplacental
The embryo and fetus have little or no immune function. They depend on the immune function of their mother. Several pathogens can cross the placenta and cause perinatal infection. Often, microorganisms that produce minor illness in the mother are very dangerous for the developing embryo or fetus. This can result in spontaneous abortion or major developmental disorders. For many infections, the baby is more at risk at particular stages of pregnancy. Problems related to perinatal infection are not always directly noticeable.
Apart from infecting the fetus, transplacental pathogens may cause placentitis (inflammation of the placenta) and/or chorioamnionitis (inflammation of the fetal membranes).