Malaria surveillance in the United States
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.