Carriers
Carriers are organisms, primarily insects or arthropods, that facilitate the transmission of pathogenic microbes from one host to another, often leading to infections in humans. Common examples include mosquitoes and ticks, which can transfer bacteria and viruses from infected animals like birds or rodents to humans through bites. Notably, diseases such as Lyme disease and malaria are associated with these vectors, with Lyme disease transmitted by black-legged ticks and malaria spread by certain mosquitoes. Prevention strategies focus on reducing exposure to these carriers by using insect repellents, wearing protective clothing, and managing environments to eliminate stagnant water where mosquitoes breed. The impact of carriers on public health is significant; for instance, malaria affects millions globally, with substantial mortality, particularly among young children. In the United States, while malaria cases are relatively low, they typically arise from travel to endemic regions. Overall, understanding carriers is crucial for disease prevention and management efforts, especially in areas where these pathogens are prevalent.
Carriers
- ALSO KNOWN AS: Vectors
Definition
A carrier is an intermediary, usually an insect or an arthropod, that transfers pathogenic microbes from an infected host to another living thing, including a human. For example, a mosquito or tick may be carrying bacteria or viruses (pathogens) from a sick bird or rodent. When the mosquito or tick bites someone, the pathogens enter the body through the break in the skin. These pathogenic microbes cause infection in the recipient, but they do not make the carrier ill.
Vector-Borne Diseases
The most commonly reported vector-borne disease in the United States is Lyme disease, which is caused by the bacterial spirochete Borrelia burgdorferi. Humans acquire it by being bitten by an infected black-legged tick. Other varieties of ticks are carriers of Rocky Mountain spotted fever caused by the bacterium Rickettsia rickettsii.
Mosquitoes may carry the Plasmodium protozoan and introduce it into humans through bites, thus causing malaria in those persons. Similarly, mosquitoes may carry the yellow fever virus and several encephalitis viruses. Transmission of these diseases to humans typically occurs in tropical regions of Africa, South Asia, and parts of South America. In the United States, mosquitoes may transmit West Nile Virus to humans after the insects have fed on infected birds.
Tularemia, caused by the bacterium Francisella tularensis, is transmitted to humans who are bitten by infected ticks and deer flies. People may also acquire tularemia from handling infected rabbits and rodents, drinking contaminated water, and inhaling contaminated dust.
Prevention and Outcomes
Vector-borne diseases may be prevented by limiting exposure to mosquitoes, ticks, flies, and fleas. People working or playing outdoors should use insect repellent; wear long-sleeved shirts, long pants, and socks in wooded areas; remove ticks promptly; wear gloves when handling sick or dead animals; and avoid mowing over dead animals. Mosquito populations may be controlled by limiting areas of stagnant water. Screens in windows and doors should be installed and maintained. In malaria-prone tropical areas, one should sleep in an enclosure of mosquito netting (a sleeping net) sprayed with insecticide.
Impact
The World Health Organization estimates that 263 million cases of malaria occurred worldwide in 2023, causing roughly 597,000 deaths, predominantly in children younger than five years of age. More than half these cases occurred in Nigeria, the Democratic Republic of the Congo, Niger, and the United Republic of Tanzania. Such cases may be treated with antimalarial drugs such as chloroquine. Vector-borne diseases from bacterial agents may be treated with antibiotics such as doxycycline and amoxicillin; those diseases caused by viral agents often require hospitalization.
Bibliography
Goddard, Jerome. Infectious Diseases and Arthropods. Totowa, N.J.: Humana Press, 2008.
Higgs, Steve. “Vector-Borne and Zoonotic Diseases Circa 2010: A Brave New World.” Vector-Borne and Zoonotic Diseases, January/February, 2010, 1-2.
"Malaria." World Health Organization, 11 Dec. 2024, www.who.int/news-room/fact-sheets/detail/malaria#:~:text=According%20to%20the%20latest%20World,to%20600%20000%20in%202022. Accessed 3 Feb. 2025.
Marquardt, William C., ed. Biology of Disease Vectors.2d ed. New York: Academic Press/Elsevier, 2005.
Schmidt, Laurie J. “Genetically Engineered Mosquitoes Are 100 Percent Resistant to Malaria Parasite.” Popular Science, July 15, 2010.