MEDICAL-FORENSIC FILES: What Happens If a Vampire Consumes Harmful Blood?

In my scenario, a girl believes she could be both a vampire and a vampire slayer. The problem with this idea is that the two bloods fight each other and eventually end up killing the host, one way or the other. I had heard that this is similar to what could happen with a fetus if the parents are of two different blood types. Is this true? If so, how can the death be prevented, and how often would the infant die without treatment?

A:        What a fascinating and clever question. Unfortunately, this is an extremely complex physiological situation and difficult to adequately explain here. But, I’ll give it a shot.

What you are referring to is Hemolytic Disease of the Newborn (HDN). It comes in many varieties and degrees of seriousness. It occurs when the fetus has a blood type that differs from the mother’s. During pregnancy, small numbers of Red Blood Cells (RBCs) pass back and forth between the mother and the fetus through the placenta. The mother’s and fetus’ blood do not directly mix as they are separated by the placental membrane. This thin tissue barrier allows oxygen and nutrients to pass, but not blood. So the two circulations (mother’s and fetus’) don’t truly mix. But, a few RBCs from each manage to slip back and forth. The child is, of course, immature as is its immune system. In fact, it is too immature to recognize the mother’s RBCs as foreign, so no immunological response occurs on the fetal side of the membrane. But, the mother’s immune system is mature and might recognize her fetus’ RBCs as foreign and construct antibodies to attack the proteins on the surface of the RBCs.

            This most commonly occurs with the Rh (Rhesus) Factor. When we say someone has A-Positive blood, we mean they are type A with a positive Rh Factor. A-negative would be type A with no Rh factor. The problem arises when the mother is Rh negative and the baby is Rh positive. This Rh positivity would come from the father. Here the Rh negative mother recognizes the RH positive antigens from the baby’s RBCs as a foreign invader, so to speak, and builds anti-Rh antibodies. These antibodies then cross the membrane back into the baby and attack and destroy the RBCs. This destruction of RBCs is called hemolysis. 

Though Rh incompatibility is the most common interaction, this can also occur with ABO blood type differences. Let’s say the mother is Type O and the baby is Type A. When the fetal Type A RBCs sneak across the membrane and into the mother, her immune system will build Anti-A antibodies. When these drift back across the placental barrier, these antibodies attack the baby’s RBCs and destroy them. 

            In either case, if only a small amount of these antibodies are created, only a small number of fetal RBCs are destroyed and the child is fine. If larger amounts are built, then the stage is set for a massive amount of the child’s RBCs to be destroyed. This can cause anemia, brain damage, kidney damage, and fetal death. When the hemoglobin in the RBCs is destroyed, a molecule called bilirubin results. This is toxic to the fetal brain and the kidneys. This process can occur anywhere between these two extremes. So, HDN can occur in almost any degree of severity.

            This interaction is typically mild with the first pregnancy, as it takes time for the mother to construct these antibodies, but their construction will increase with each subsequent mismatched pregnancy. The first pregnancy starts the process and those that follow make it worse. 

The treatment for the baby might include exchange blood transfusions and exposure to UV light---either the sun or an artificial UV source. UV light breaks apart the bilirubin molecules and lessens the likelihood of brain damage. This damage is known as kernicterus. 

            The preventive treatment is to give the RH negative mother a substance called RhoGAM. It basically blocks the mother’s immune system from producing the antibodies that damage the baby’s RBCs. This is usually given in the first 20 or so weeks of the pregnancy in a Rh negative mother if it is discovered that the fetal blood type if Rh positive. It is also given the Rh Negative mother’s after delivery of a Rh positive child to help prevent problems with future non-compatible  pregnancies.

            Told you this was complex. And this is just the very basics.

            So, your vampire could ingest the wrong blood and something similar could happen. With the first ingestion, nothing occurs, but with future ingestions of the “bad” blood, she could feel ill. Maybe headaches, nausea, anemia with fatigue and weakness, rashes and itching, and almost any other symptoms you want. These will get worse with each ingestion. But, maybe there is a RhoGAM-like substance available and she gets the injection and becomes resistant to the interaction. Since this is a fantasy story you can incorporate some of this and take your story in any direction you want.

DP Lyle, MD

www.dplylemd.com

This question originally appeared in MORE FORENSICS & FICTION by DP Lyle