Vertically transmitted infection

A vertically transmitted infection is an infection caused by bacteria, viruses or, in rare cases, parasites transmitted directly from the mother to an embryo, fetus or baby during pregnancy or childbirth. It can occur when the mother gets an infection as an intercurrent disease in pregnancy.

Nutritional deficiencies may exacerbate the risks of perinatal infection.

Classification
The transmission can also be called mother-to-child transmission.

A vertically transmitted infection can be called a perinatal infection if it is transmitted in the perinatal period, which is the period starting at a gestational age of 22 to 28 weeks (with regional variations in the definition) and ending 7 completed days after birth.

The term congenital infection can be used if the vertically transmitted infection persists after childbirth.

Examples
Several vertically transmitted infections are included in the TORCH complex, which stands for:
 * 1) T – Toxoplasmosis / Toxoplasma gondii
 * 2) O – Other infections (see below)
 * 3) R – Rubella
 * 4) C – Cytomegalovirus
 * 5) H – Herpes simplex virus-2 or neonatal herpes simplex

The "other agents" under O include:
 * Coxsackievirus
 * Chickenpox (caused by varicella zoster virus)
 * Parvovirus B19
 * Chlamydia
 * HIV
 * Human T-lymphotropic virus
 * Syphilis

Hepatitis B may also be classified as a vertically transmitted infection, but the hepatitis B virus is a large virus and does not cross the placenta, hence it cannot infect the fetus unless there have been breaks in the maternal-fetal barrier, such as 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, Syphilis.

A further expansion of this acronym, CHEAPTORCHES, was proposed by Ford-Jones and Kellner in 1995:
 * C – Chickenpox and shingles
 * H – Hepatitis B, C, (D), E
 * E – Enteroviruses
 * A – AIDS (HIV infection)
 * P – Parvovirus B19
 * T – Toxoplasmosis / Toxoplasma gondii
 * O – Other (Group B Streptococcus, Listeria, Candida, Lyme disease)
 * R – Rubella
 * C – Cytomegalovirus
 * H – Herpes simplex
 * E – Everything else sexually transmitted (Gonorrhea, Chlamydia, Ureaplasma urealyticum, Human papillomavirus)
 * S – Syphilis

Signs and symptoms
The signs and symptoms of a vertically transmitted infection depend on the individual pathogen. It may cause subtle signs such as a influenza-like illness and may not even be noticed by the mother during the pregnancy. In such cases, the effects may be seen first at birth.

Symptoms of a vertically transmitted infection may include fever and poor feeding. 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 mother often has a mild infection with few or no symptoms.

It is possible for genetic conditions (Aicardi-Goutieres syndrome) to present in a similar manner.

Causes
The main routes of transmission of vertically transmitted infections are across the placenta (transplacental) and across the female reproductive tract during childbirth:

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.

During childbirth
Babies can also become infected by their mother during birth. Some infectious agents may be transmitted to the embryo or fetus in the uterus, while passing through the birth canal or even shortly after birth. The distinction is important because when transmission is primarily during or after birth, medical intervention can help prevent infections in the infant.

During birth, babies are exposed to maternal blood and body fluids without the placental barrier intervening and to the maternal genital tract. Because of this, blood-borne microorganisms (Hepatitis B, HIV), organisms associated with sexually transmitted disease (e.g., Gonorrhoea and Chlamydia), and normal fauna of the genito-urinary tract (e.g., Candida) are among those commonly seen in infection of newborns.

Virulence versus symbiosis
In the spectrum of optimal virulence, vertical transmission tends to evolve benign symbiosis. It is therefore a critical concept for evolutionary medicine. Because a pathogen's ability to pass from parent to child depends significantly on the hosts' ability to reproduce, pathogens' transmissibility tends to be inversely related with their virulence. In other words, as pathogens become more harmful to and thus decrease the reproduction rate of their host organism, they are less likely to be passed on to the hosts' offspring, since there will be fewer offspring.

Although AIDS is sometimes transmitted through perinatal transmission, its virulence can be accounted for by the fact that its primary mode of transmission is not vertical. Moreover, medicine has further decreased the frequency of vertical transmission of AIDS. The incidence of perinatal AIDS cases in the United States has declined as a result of the implementation of recommendations on HIV counselling and voluntary testing practices and the use of zidovudine therapy by providers to reduce perinatal HIV transmission.

The price paid in the evolution of symbiosis is, however, great: for many generations, almost all cases of vertical transmission will continue to be pathological—in particular if there are any other routes of transmission. It takes many generations of random mutation and selection to evolve symbiosis. During this time, the vast majority of vertical transmission cases will exhibit the initial virulence.

In Dual Inheritance Theory, vertical transmission refers to the passing of cultural traits from parents to children.

Diagnosis
When physical examination of the newborn shows signs of a vertically transmitted infection, the examiner may test blood, urine, and spinal fluid for evidence of the infections listed above. Diagnosis can be confirmed by culture of one of the specific pathogens or by increased levels of IgM against the pathogen.

Treatment and prevention
Some of the vertically transmitted infections, such as toxoplasmosis and syphilis, can be effectively treated with antibiotics if the mother is diagnosed early in her pregnancy. Many of the viral vertically transmitted infections have no effective treatment, but some, notably rubella and varicella-zoster, can be prevented by vaccinating the mother prior to pregnancy.

If the mother has active herpes simplex (as may be suggested by a pap test), delivery by Caesarean section can prevent the newborn from contact, and consequent infection, with this virus.

It has been suggested that IgG2 antibody can play crucial role in prevention of intrauterine infections and currently extensive research is going on for developing IgG2 based therapies for treatment and vaccination.

Prognosis
Each type of vertically transmitted infection has a different prognosis. The stage of the pregnancy at the time of infection also can change the effect on the newborn.