How to Diagnose Mosquito-Borne Diseases
Mosquito-borne diseases are transmitted when a mosquito ingests viruses, parasites, or bacteria from a host and injects them into another individual
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Vectors are living organisms, such as mosquitoes, capable of transmitting infectious disease between humans or animals. Mosquito-borne diseases are transmitted when a mosquito ingests viruses, parasites, or bacteria from a host and injects them into another individual. Accurate diagnosis is required to ensure appropriate clinical management. A variety of diagnostic methods are available for different mosquito-borne diseases.
Chikungunya
Transmission: Aedes mosquitoes
Organism: RNA virus
Symptoms: Fever, severe (often debilitating) joint pain, muscle pain, headache, nausea, fatigue, and rash.
Diagnostic methods: Serological tests, including ELISA to confirm IgM and IgG anti-chikungunya antibodies. Samples collected within the first week of symptom onset should be tested with serological (ELISA) and virological (RT-PCR) methods.
Zika virus
Transmission: Aedes mosquitoes
Organism: Flavivirus
Symptoms: Many infected individuals do not exhibit symptoms. Those that do often experience fever, rash, conjunctivitis, muscle and joint pain, malaise and headache. Infection during pregnancy is associated with microcephaly and congenital malformations in infants.
Diagnostic methods: In patients experiencing symptom onset in under seven days, nucleic acid testing (NAT) is used for the detection of viral RNA or DNA. A negative NAT result should be considered with caution, as viraemia declines rapidly following seven days of symptom onset, and may evade detection. Serological methods for IgM detection are suitable for patients presenting with symptom onset after seven days.
Dengue
Transmission: Aedes mosquitoes
Organism: Flavivirus with four distinct serotypes: DEN 1, DEN 2, DEN 3, and DEN 4.
Symptoms: typically appear three to fourteen days post-infection. Dengue should be suspected in the presence of fever and any two of the following symptoms: severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen glands, or rash. Severe cases may be lethal due to fluid accumulation, respiratory distress, and organ impairment, among other factors.
Diagnostic methods: In the early stages of infection, up to six days after the onset of symptoms, viral isolation and serotype identification, nucleic acid detection, and antigen detection are suitable diagnostic methods. In the later stages of infection, seven days or longer after the onset of symptoms, serological methods are advised. IgM Antibody Capture ELISA (MAC-ELISA) relies on capturing human IgM antibodies using anti-human IgM and the addition of dengue virus antigens derived from envelope proteins of the four dengue serotypes. The Plaque Reduction Neutralization Test (PRNT) detects neutralizing antibodies against dengue in serum. PRNT testing is important to determine the cause of infection among patients for whom a specific diagnosis is essential (i.e. pregnancy).
West Nile Virus
Transmission: Culex mosquitoes
Organism: Flavivirus
Symptoms: Approximately twenty percent of infected individuals will develop West Nile fever, with symptoms including fever, headache, fatigue, body aches, nausea, vomiting, skin rash, and swollen lymph glands. In severe cases, West Nile encephalitis or meningitis, or West Nile poliomyelitis can occur. Symptoms include headache, high fever, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis.
Diagnostic methods: Several different methods may be used to diagnose West Nile virus. ELISA is used to determine IgG antibody seroconversion via analysis of two specimen, collected at a one-week interval. IgM antibody capture ELISA may also be used for diagnosis. Serum IgM antibody may be detected up to a year after infection, while cerebrospinal fluid IgM is frequently detected at the time of clinical presentation. Neutralization assays, virus isolation via cell culture, and viral detection via RT-PCR are also suitable diagnostic methods.
Malaria
Transmission: Anopheles mosquitoes
Organism: Protozoa of the genus Plasmodium (P. malariae, P. ovale, P. vivax, and P. falciparum)
Symptoms: fever, chills, headache, myalgias, nausea, vomiting, and occasionally diarrhea and abdominal pain. The malarial paroxysm has three stages: cold stage lasting 15-60 minutes with shivering, the hot stage lasting 2-6 hours with high fever, flushed dry skin, headache, nausea, and vomiting, and the sweating stage lasting 2-4 hours with declining fever and profuse sweating.
Diagnostic methods: A blood smear may be stained with Giemsa and examined for the presence of the parasite. Fluorescent microscopy and acridine-orange staining have also been used for identification of malarial parasites. When microscopy is unavailable, rapid diagnostic tests (RDTs) may be used to detect malaria parasites in the blood. RDTs rely on dye-labeled antibody capture, whereby the dye-labeled antibody binds the parasite and is subsequently captured on a strip to produce a line in the visible window.
Additional methods to determine past exposure, such as serological methods like the indirect fluorescent antibody (IFA) test and ELISA. PCR may be used to detect parasitic nucleic acids, but is considered more valuable for the determination of the species of parasite as it may be more time consuming than other point-of-care tests.
Yellow Fever
Transmission: Aedes mosquitoes
Organism: Arbovirus of Flavivirus genus
Symptoms: Many infected individuals do not exhibit symptoms. Those that do experience fever, muscle pain (with prominent backache), headache, loss of appetite, and nausea or vomiting after an incubation period of three-to-six days. Some individuals will progress to a second phase within 24 hours of symptom onset, characterized by high fever, jaundice, dark urine, abdominal pain, vomiting, bleeding from the mouth, nose, eyes or stomach.
Diagnostic methods: Diagnostic methods differ based on the stage of infection. In early stages, PCR may be suitable to detect the virus in blood or urine. In later stages, ELISA is used to identify anti-YFV IgM antibodies, or the PRNT test is used to detect neutralizing antibodies directed toward yellow fever virus.