Good morning all,
As you know, I try to send you an article from the science news each week that is relevant to a recent topic we have considered in our class. Some weeks, that requires a little bit of digging, a little reading beyond my usual outlets for science news. This week, however, there is no need to look far, or wide. Our most recent lecture was on immunity, and the science news has been FULL of stories about the immune system, nearly the entire semester.
This week, there are two major news stories related to immune system function. The first of these is just breaking, and will surely be followed by more news to come: the first widespread use of a vaccine against malaria in Africa. We do not hear much about malaria in this country (even though several thousand cases occur in the U.S. every year), but it is a tropical scourge across much of the globe. It is caused by the malarial parasite Plasmodium falciparum, carried by mosquitoes and transferred between human hosts by their bites. It is very infectious - estimates suggest that more than 200,000,000 (that's 200 million) cases occur each year. It's also very deadly, causing >400,000 deaths per year. Children are especially vulnerable. I heard a news report this week that estimated that every 2 minutes, an African child dies of malaria.
As a disease, malaria is very problematic. Its mosquito hosts are very numerous, widespread, difficult to control, and difficult to avoid. The parasite passes directly into the human host circulatory system during a mosquito blood meal, where it takes up residence inside of red blood cells. Remember that disease agents that get inside of our cells are hard to combat - they are at least partially hidden/protected from immune surveillance, and should they be detected and their host cell destroyed, it results in the net loss of functional host cells, potentially even releasing more parasites to infect other cells. Persons suffering from malaria have symptoms ranging from mild (tiredness, chills, aches) to severe (high fevers, blood clots, kidney damage), and aggressive treatment with anti-parasitic drugs (such as Chloroquine) is normally required. Anti-parasitic drugs can also be used prophylactically (e.g., to prevent infection before it happens), but their efficacy is not perfect and varies considerably against the different strains of the malarial parasite. For all of these reasons, an effective vaccine would be a great benefit.
In the news this week is report of the first widespread use of a moderately-effective, inexpensive, anti-malaria vaccine. It was developed over the last 30 years, following promising laboratory studies (the development of a pharmaceutical, from lab bench to use in human populations, can be VERY long). It is suggested to be only ~30% effective in protecting against malaria. But, if 30% of the hundreds of thousands of deaths that occur each year can be prevented, it will be very worthwhile - imagine being able to create a vaccine that prevents 100,000 deaths each year! In addition, much will be learned from this first really large human trial of the vaccine, and the data that will be collected on its efficacy will likely lead to improvements in the vaccine itself.
The other big story related to immunity this week also relates to infectious disease and immunizations, this time for measles. Measles is a very highly infectious disease caused by the measles virus. It causes rashes, aches, and often dangerously-high fevers, and can be fatal to vulnerable subjects. In most developed parts of the world, measles has largely been eradicated, through successful development and use of the measles vaccine, commonly given as one part of the MMR (measles-mumps-rubella) vaccine. Very recently, however, there are severe outbreaks of measles in several locations in this country (including New York City).
These recent outbreaks in the U.S. have been caused by a combination of two factors. The first is a reduced number of parents having their children vaccinated against measles, in large part due to false information about the potential harm caused by vaccines. Over the past decade, several widely reported (but now discredited) stories have circulated about the use of the preservative thimerosol in vaccines, which has led some to believe that the vaccines themselves are more dangerous than the diseases they are designed to prevent. In addition, the vaccine is so effective that measles is rarely reported, so many believe that it is no longer even necessary. Together, these cause lower rates of vaccination in some populations.
The other causative agent is the introduction of the disease from elsewhere, in these cases from travelers who visited areas in the Middle East, picked-up the virus, and brought it back to their U.S. communities. The symptoms of measles may not appear for weeks after exposure, so persons who carry the virus but do not yet realize it can very easily pass it unknowingly to others.
Vaccinations protect individuals if they encounter an agent of disease, because it primes their immune systems (remember those memory cells?) to make rapid and robust responses upon subsequent exposure to an antigen, such as that of the measles virus. Vaccinations also work at a population level, by reducing the likelihood of encountering a disease in the first place. This is the concept of "herd immunity" - if everyone in a population is vaccinated, the chances of encountering someone who could pass on the disease is very low. Measles is extremely infectious (via sneezing/coughing), such that ~95% vaccination rates are necessary for "herd immunity" against measles to be available. In select populations, immunization rates have fallen well below this level.
This combination of factors (reduced immunization rates, highly infectious virus) leads to disease outbreaks. In addition to large outbreaks in New York and Washington state, several college campus in California began quarantining personnel, in an attempt to control measles outbreaks.
Just as our immune systems are wonderfully adapted to protect us from agents of disease, so too are those same agents of disease evolved to evade our immune defenses. It's an evolutionary 'arms race', and, left on its own, would continue that way. Vaccinations give us a terrific advantage against some infectious diseases - but only if those vaccines are safe, available, and accepted. Are they perfect? Of course not - but the scientific community is very much in agreement that they are better than facing the risks without them. If you hear of anyone near you having measles, make sure that you and your family are protected.
Have a great weekend -