Malaria surveillance in the United States

Plasmodium infected human erythrocytes

Malaria is a disease that currently is endemic in vast areas of the tropics, and afflicts an estimated 200 million people worldwide  (roughly three percent of the Earth’s population) at present. Those cases resulted in over 600,000 deaths in 2010 alone. Since malaria poses such a significant global health risk, and because the range of the disease can potentially shift due to climate change, it is a ‘notifiable’ disease with the Centers for Disease Control.

The March 2, 2012 issue of Morbidity and Mortality Weekly Report contains the CDC’s malaria surveillance report for calendar year 2010. The report summarizes epidemiological data collected from all cases of malaria reported to health care workers in the United States, along with the presumed route of acquisition for each of the cases. The US is considered “malaria-free”, and any cases that are observed are typically tracked back to individuals who have traveled elsewhere and acquired the pathogen. In calendar year 2010, 1691 cases of malaria were reported to the CDC. 

Malaria is caused by the protozoan parasite Plasmodium, and is typically diagnoses on the basis of symptomology, along with confirmatory blood smears and other diagnostic tests. Malaria on its own is not contagious from individual to individual, and requires a mosquito to transmit the pathogen into a naive host. Consequently, cases of malaria that are diagnosed in the United States occur in individuals who have traveled to a region where Plasmodium and the mosquito are found, or have acquired through another means such as blood transfusion from contaminated blood. Because of the possibility of malaria gaining a foothold by reintroduction into breeding mosquito populations in the southern US, the CDC is very concerned about the disease, and closely monitors the causes of cases as they arise on an annual basis.

The data collected for 2010 indicated that out of the almost 1700 cases, all but three of them were found to be “imported,” and in those cases the patient had recently traveled to a malaria-endemic region. One of the remaining cases was attributable to a blood transfusion, and the other two were classified as “cryptic” with no demonstrable cause, but with no evidence for mosquito-borne transmission here in the United States. The number of cases in 2010 was the highest in 30 years, and the increase in that year mirrored similar increases in other industrialized countries.

Despite the lack of evidence indicating emergence of malaria transmitted by mosquitoes in the United States, the CDC remains concerned about the elevated levels of the disease during the most recent reporting period. Individuals who travel outside of the United States are urged to contact their primary health caregivers for advice about prophylactic measures that can be taken to avoid malaria infection. The Centers for Disease Control maintains a list of recommended medications that can be taken to prevent infection of malaria, however it is important to note that drugs effective in one geographical area may be ineffective elsewhere. The CDC notes in their annual report that patients who did report taking prophylactic measures to avoid infection frequently failed to be fully compliant with the recommended doses, and that education measures will continue to be the most effective mechanism to minimize malaria in this country.

Advertisements

About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on March 8, 2012, in Danger danger danger!, Microbes in the News and tagged , , . Bookmark the permalink. 2 Comments.

  1. Andrea Hetrick

    This article was very interesting to me because it relates to what we are learning in chapter 14 of the class currently. Malaria is considered to be a parasite and it benefits from its host, this is considered a symbiotic relationship. This disease can only be transmitted from animal to human, which is an animal reservoir called zoonosis. It was intriguing for me to read in the article because not many cases originated from the United States, but instead came from travelers in different countries. This is why in much poorer countries than ours malaria is a vicious disease because they do not have the proper medications or education of the general population. My concern when reading this article is because there are five different types of malaria reported today, how long until it catches up with our medication. Mosquitoes can carry many diseases but the life cycle is very short, which makes me wonder if they will ever be able to pass this disease onto their offspring in their eggs from the mother. The blood they feed off their host can have disease in the blood, that blood that the female takes why is the disease not transferred to her offspring? This article also got me thinking that if the infected hosts were able to transmit to their offspring and cause random mutation, it could spread more easily to the United States causing concern to our new medicine. It amazes me about how much genetics comes into play in sucessibility on who can get a disease whether it is a human or animal host.

    • In the Unseen Life class at York College, I pose an exam question to the students to suggest which of 5 diseases that we have studied presents the most significant public health risk to us today: Bubonic Plague, Influenza, Hemophilia, Irish Potato Blight, or Malaria.

      Several of those pose low to minimal risk to us (see for example, this post on the blog about the Black Death). Hemophila is something that is genetically determined, and not infectious. Irish Potato Blight itself is unlikely, but could potentially arise due to our tendency towards plant monoculture. Influenza of course varies from year to year, but we can make pretty good predictions about what virus types are prevalent, and vaccinate accordingly.

      So we are left with malaria, which currently affects a majority of the planet’s population and is frequently becoming resistant to treatments. As you noted, even here in the United States we are at risk for malaria spreading, and this worry is increasing with the possibility of sea levels rising in the future making more mosquito breeding areas.

      Plasmodium requires BOTH the mosquito and a mammal to complete its life cycle. The protozoan reproduces in the mosquito, and undergoes sexual reproduction in the salivary gland of the mosquito, but is not passed onto the offspring of the mosquito. Likewise, the protozoan undergoes asexual reproduction in a mammal, but is not passed onto the fetus, and is not communicable (e.g. someone with malaria is not contagious to another person), unless bitten by a mosquito.

%d bloggers like this: