Arthropod vectors, including mosquitoes, ticks, fleas, and mites, that feed on vertebrate hosts can spread bacteria, protozoa, and viruses during feeding to their susceptible host, resulting in a variety of infections and diseases. Arboviruses (arthropod-borne viruses) include Zika virus, West Nile virus (WNV), chikungunya virus, dengue virus (DENV), yellow fever virus (YFV), and Colorado tick fever virus (CTF) to name a few. Malaria and babesiosis are both conditions caused by arthropod-borne protozoan parasites, Plasmodium and Babesia, respectively. Conditions caused by arthropod-borne bacteria include rickettsial diseases, ehrlichiosis, anaplasmosis, and Lyme disease, as well as other Borrelia-associated disorders (Calisher, 1994; CDC, 2024s). Isolation, identification, and characterization of these various infections depend on the causative agent. Identification methods may include culture testing, microscopy, and staining techniques; moreover, molecular testing, such as nucleic acid amplification testing (NAAT), and serologic testing, including immunofluorescence antibody assays and enzyme-linked immunosorbent assays (ELISA), can be used for laboratory diagnosis (Miller et al., 2024).

For Lyme disease and testing for Borrelia burgdorferi, please see CAM 159 Lyme Disease.

Policy 
Application of coverage criteria is dependent upon an individual’s benefit coverage at the time of the request. 

1. For individuals suspected of having babesiosis (see Note 1), the use of a Giemsa- or Wright-stain of a blood smear or nucleic acid amplification testing (NAAT) is considered MEDICALLY NECESSARY.
2. For individuals suspected of having babesiosis (see Note 1), the use of either an IgG or IgM indirect immunofluorescence antibody (IFA) assay for Babesia is considered NOT MEDICALLY NECESSARY.
3. For individuals suspected of having a relapsing fever caused by a Borrelia spp., the following testing is considered MEDICALLY NECESSARY:
   1. For individuals suspected of having hard tick relapsing fever (HTRF) (see Note 2): serologic assays to detect Borrelia antibodies or PCR testing to detect Borrelia miyamotoi.
   2. For individuals suspected of having louse-borne relapsing fever (LBRF) (see Note 3): peripheral blood smear microscopy or PCR testing to detect Borrelia recurrentis.
   3. For individuals suspected of having a soft tick relapsing fever (STRF)/tickborne relapsing fever (TBRF) (see Note 4): dark-field microscopy of a peripheral blood smear, microscopy of a Wright- or Giemsa-stained blood smear, PCR testing to detect Borrelia spp., or serologic assays to detect Borrelia antibodies.
4. For individuals suspected of having a relapsing fever caused by a Borrelia spp., culture testing for Borrelia is considered NOT MEDICALLY NECESSARY.
5. For individuals suspected of having chikungunya (see Note 5), the use of viral culture for diagnosis, NAAT for the presence of chikungunya in a serum sample, or IFA assay for IgM antibodies during both the acute and convalescent phases is considered MEDICALLY NECESSARY.
6. For individuals suspected of having Colorado tick fever (CTF) (see Note 6), the use of PCR testing or IFA for CTF-specific IgM antibodies is considered MEDICALLY NECESSARY.
7. For the detection of dengue virus (DENV), the use of NAAT, IgM antibody capture ELISA (MAC-ELISA), or NS1 ELISA, as well as a confirmatory plaque reduction neutralization test for DENV, is considered MEDICALLY NECESSARY in the following individuals:
   1. For individuals suspected of having a DENV infection (see Note 7).
   2. For individuals who are symptomatic for Zika virus infection (see Note 8).
8. For individuals suspected of having DENV (see Note 7), the use of IgG ELISA or hemagglutination testing is considered NOT MEDICALLY NECESSARY.
9. For individuals suspected of having ehrlichiosis and/or anaplasmosis (see Note 8), the use of NAAT of whole blood, IFA assay for IgG antibodies, or microscopy for morulae detection is considered MEDICALLY NECESSARY.
10. For individuals suspected of having ehrlichiosis and/or anaplasmosis (see Note 8), the use of an IFA assay for IgM antibodies or standard blood culture is considered NOT MEDICALLY NECESSARY.
11. For individuals suspected of having malaria (see Note 10), the use of a rapid immunochromatographic diagnostic test or smear microscopy to diagnose malaria, determine the species of Plasmodium, identify the parasitic life-cycle stage, and/or quantify the parasitemia (can be repeated up to three times within three days if initial microscopy is negative in suspected cases of malaria) is considered MEDICALLY NECESSARY.
12. To confirm the species of Plasmodium in an individual diagnosed with malaria, PCR testing is considered MEDICALLY NECESSARY.
13. For individuals suspected of having malaria (see Note 10), the use of IFA for Plasmodium antibodies is considered NOT MEDICALLY NECESSARY.
14. For individuals suspected of having a rickettsial disease (see Note 11), the use of an IFA assay for IgG antibodies (two tests occurring a minimum of two weeks apart) is considered MEDICALLY NECESSARY.
15. For individuals suspected of having a rickettsial disease (see Note 11), the use of standard blood culture, NAAT, or IFA assay for IgM antibodies is considered NOT MEDICALLY NECESSARY.
16. For individuals suspected of having West Nile virus (WNV) disease (see Note 12), the use of IFA for WNV-specific IgG or IgM antibodies in either serum or CSF and a confirmatory plaque reduction neutralization test for WNV is considered MEDICALLY NECESSARY.
17. To confirm a WNV infection in individuals who are immunocompromised, nucleic acid detection of WNV is considered MEDICALLY NECESSARY.
18. For immunocompetent individuals suspected of having WNV disease (see Note 12), the use of NAAT for WNV is considered NOT MEDICALLY NECESSARY.
19. For individuals suspected of having a yellow fever virus (YFV) infection (see Note 13), the use of NAAT for YFV or serologic assays to detect virus-specific IgM and IgG antibodies, as well as a confirmatory plaque reduction neutralization test for YFV, is considered MEDICALLY NECESSARY.
20. For the detection of Zika virus, the use of NAAT is considered MEDICALLY NECESSARY in the following individuals:
    1. Up to 12 weeks after the onset of symptoms for symptomatic (see Note 8) pregnant individuals who, during pregnancy, have either lived in or traveled to areas with current or past Zika transmission or who have had sex with someone who either lives in or has recently traveled to areas with current or past Zika virus transmission (see Note 14).
    2. For symptomatic non-pregnant individuals living in or with recent travel to an area with an active CDC Zika Travel Health Notice or an area with current or past Zika virus transmission (see Note 14) when symptoms presented within the last seven days.
21. Zika virus NAAT and Zika virus IgM testing, as well as a confirmatory plaque reduction neutralization test for Zika, is considered MEDICALLY NECESSARY in any of the following situations:
    1. Up to 12 weeks after the onset of symptoms for symptomatic (see Note 8) pregnant individuals who, during pregnancy, have either lived in or traveled to areas with an active CDC Zika Travel Health Notice or who have had sex with someone who either lives in or has recently traveled to areas with an active CDC Zika Travel Health Notice (see Note 14).
    2. For pregnant individuals who have a fetus with prenatal ultrasound findings consistent with congenital Zika virus infection (see Note 15).
    3. For infants born from individuals who, during pregnancy, tested positive for Zika virus.
    4. For infants born with signs and symptoms of congenital Zika syndrome (see Note 15) and who have a birthing parent who had a possible Zika virus exposure during pregnancy.
    5. For symptomatic non-pregnant individuals living in or with recent travel to an area with an active CDC Zika Travel Health Notice or an area with current or past Zika virus transmission (see Note 14) when symptoms presented more than seven days prior to testing.
22. For non-pregnant individuals who have not traveled outside of the United States and its territories and who are symptomatic for Zika virus infection (see Note 8), NAAT and/or IgM testing for Zika detection is considered NOT MEDICALLY NECESSARY.
23. For asymptomatic individuals, testing for babesiosis, chikungunya virus, CTF, DENV, ehrlichiosis and/or anaplasmosis, malaria, rickettsial disease, TBRF, WNV, YFV, or Zika virus during a general exam without abnormal findings is considered NOT MEDICALLY NECESSARY.

NOTES:

Note 1: Typical signs and symptoms of babesiosis can include hemolytic anemia, splenomegaly, hepatomegaly, jaundice, and nonspecific flu-like symptoms such as fever, chills, body aches, weakness, and fatigue (CDC, 2024j).

Note 2: Typical signs and symptoms of HTRF (caused by Borrelia miyamotoi) can include chills or shakes, fatigue, nausea or vomiting, headache, and muscle and joint aches (CDC, 2024a).

Note 3: Typical signs and symptoms of LBRF (caused by Borrelia recurrentis) can include fever, headache, chills or shakes, muscle and joint aches, and nausea. Though the clinical symptoms of LBRF are similar to STRF, LBRF is usually associated with fewer relapses (CDC, 2024b)

Note 4: Typical signs and symptoms of STRF/TBRF (caused by Borrelia hermsii, B. turicatae, and other Borrelia bacteria) can include fever, headache, muscle aches, chills, dizziness, joint pain, nausea and vomiting, appetite loss, and rarely, facial paralysis eye pain or redness, or vision changes (CDC, 2024c).

Note 5: Typical signs and symptoms of chikungunya include high fever (> 102◦F or 39◦C), joint pains (usually multiple joints, bilateral, and symmetric), headache, myalgia, arthritis, conjunctivitis, nausea, vomiting, and maculopapular rash (Staples et al., 2024).

Note 6: Typical signs and symptoms of CTF can include fever, chills, headache, myalgia, malaise, sore throat, vomiting, abdominal pain, and maculopapular or petechial rash (CDC, 2024e).

Note 7: Typical signs and symptoms of dengue include fever, headache, retro-orbital eye pain, myalgia, arthralgia, macular or maculopapular rash, petechiae, ecchymosis, purpura, epistaxis, gingival bleeding, hematuria, leukopenia, thrombocytopenia, hyponatremia, elevated AST and ALT, and nausea and/or vomiting (CDC, 2024f, 2024r).

Note 8: Typical signs and symptoms of Zika virus infection can include fever, rash, headache, joint pain, conjunctivitis (red eyes), and muscle pain (CDC, 2024t).

Note 9: Typical signs and symptoms of ehrlichiosis and/or anaplasmosis usually begin 5 – 14 days after an infected tick bite, and they include fever, headache, malaise, myalgia, and shaking chills. Ehrlichiosis can also present with gastrointestinal issues, including nausea, vomiting, and diarrhea (Biggs et al., 2016).

Note 10: Typical signs and symptoms of malaria can include fever, influenza-like symptoms (e.g., chills, headache, body aches), anemia, jaundice, seizures, mental confusion, kidney failure, and acute respiratory distress syndrome (Tan & Abanyie, 2024).

Note 11: Typical signs and symptoms of rickettsial diseases (including Rocky Mountain spotted fever, Rickettsia parkeri rickettsiosis, Rickettsia species 364D rickettsiosis, Rickettsia spp. (mild spotted fever), and R. akari (rickettsialpox)) usually begin 3 – 12 days after initial bite and can include fever, headache, chills, malaise, myalgia, nausea, vomiting, abdominal pain, photophobia, anorexia, and skin rash. Rickettsia species 364d rickettsiosis can also present with an ulcerative lesion with regional lymphadenopathy (Biggs et al., 2016).

Note 12: Typical signs and symptoms of WNV include headache, myalgia, arthralgia, gastrointestinal symptoms, and maculopapular rash. Less than 1% of infected individuals develop neuroinvasive WNV with symptoms of meningitis, encephalitis, or acute flaccid paralysis (Nasci et al., 2013).

Note 13: Typical signs and symptoms of yellow fever include symptoms of the toxic form of the disease (jaundice, hemorrhagic symptoms, and multisystem organ failure), as well as nonspecific influenza symptoms (fever, chills, headache, backache, myalgia, prostration, nausea, and vomiting in initial illness) (Gershman & Staples, 2024).

Note 14: The CDC provides information on the geographic risk classifications of Zika (https://www.cdc.gov/zika/geo/index.html), as well as providing travel health notices for pathogens of concern (https://wwwnc.cdc.gov/travel/notices). 

Note 15: Typical signs and symptoms of congenital Zika syndrome can include microcephaly, problems with brain development, feeding problems (e.g., difficulty swallowing), hearing loss, seizures, vision problems, decreased joint movement (i.e., contractures), and stiff muscles (making it difficult to move) (CDC, 2024n).

Table of Terminology

Rationale
Hematophagous arthropods, such as mosquitoes, ticks, fleas, and mites, can spread opportunistic bacteria, protozoa, and viruses to host organisms when feeding. Numerous outbreaks of arthropod-borne disease have been documented, including plague, an acute febrile disease caused by Yersinia pestis through the bite of infected fleas, which resulted in more than 50 million deaths in Europe alone during the “Black Death” outbreak. More than 3000 cases of plague were reported to the World Health Organization (WHO) between 2010 and 2015 with 584 deaths. Today, most cases of plague occur in the Democratic Republic of Congo, Madagascar, and Peru (WHO, 2022b).

The Centers for Disease Control and Prevention (CDC) reported a large increase in the number of vector-borne diseases within the United States and its territories between 2004-2016. More than 640,000 cases were reported during that time; in fact, infections of tickborne bacteria and protozoa more than doubled from 2004 to 2016. “In the United States, 16 vector-borne diseases are reportable to state and territorial health departments, which are encouraged to report them to the National Notifiable Disease Surveillance System (NNDSS). Among the diseases on the list that are caused by indigenous pathogens are Lyme disease (Borrelia burgdorferi); West Nile, dengue, and Zika virus diseases; plague (Yersinia pestis); and spotted fever rickettsioses (e.g., Rickettsia rickettsii). Malaria and yellow fever are no longer transmitted in the United States but have the potential to be reintroduced” (Rosenberg et al., 2018). New vector-borne infections are emerging; for example, two unknown, life-threatening RNA viruses spread by ticks have been identified in the U.S. since 2004. Although both tick- and mosquito-borne diseases are increasing across the U.S., the CDC reports that these two vectors are showing different trends. The mosquito-borne diseases are characterized by epidemics; for example, West Nile Virus is essentially limited to the continental U.S. but has spread rapidly since its introduction to New York in 1999, whereas chikungunya and dengue primarily occur within the U.S. territories. On the other hand, the tickborne disease increase occurs in the continental U.S. and has experienced a gradual, steady rate increase with Lyme disease comprising 82% of all tickborne diseases (Rosenberg et al., 2018). Figure 1 and 2 below, taken from Rosenberg et al. (2018), show the reported cases of tickborne and mosquito-borne disease in the United States from 2004-2016.

Rickettsial infections
Rocky Mountain spotted fever (RMSF) is the most common rickettsial infection in the U.S. with 6,248 cases reported to the CDC alone in 2017 (CDC, 2024q). RMSF is caused by Rickettsia rickettsii, spread in the U.S. predominantly by Dermacentor variabilis (the American dog tick) and D. andersoni (the Rocky Mountain wood tick), and can be found throughout North America as well as parts of South America. The Council for State and Territorial Epidemiologists combined RMSF with other rickettsial diseases into the more broad “spotted fever rickettsiosis” designation in 2010 (CDC, 2024q). Besides the obligatory tick bite, typical symptoms of RMSF include fever, headache, and rash with the characteristic rash occurring in approximately 88% to 90% of patients within three to five days of illness. If left untreated, RMSF can be fatal but can easily be treated with antimicrobial therapy upon timely diagnosis. Definitive diagnosis of RMSF cannot usually be made via culture because Rickettsia cannot be grown in cell-free culture media; they are obligate intracellular bacteria requiring living host cells. RMSF diagnosis can be made via either skin biopsy prior to treatment with antibiotics or through serologic testing using IFAs. Immunoglobulin G (Biggs et al.) antibodies are more specific than immunoglobulin M (IgM) antibodies since the latter can give false-positive results due to cross-reactivity with other bacterial pathogens. A drawback of IFA is that usually it is unreliable for the first five days of infection until antibody levels are high enough for detection. The CDC and major clinical labs do offer a polymerase chain reaction (PCR)-based assay for RMSF (McClain, 2024a). 

Since 2001, thirteen more human Rickettsiae belonging to the spotted fever group (SFG) have been identified. All SFGs can cause fever, headache, and myalgia and are arthropod-borne (primarily ticks and mites). Most patients with an SFG display a rash and/or a localized eschar. Rickettsialpox, caused by R. akari, is transmitted from the bite of a house mouse mite, usually after mouse extermination programs result in a decrease of the mite’s food supply. Rickettsialpox is typically a relatively mild disease that can resolve itself without treatment within three weeks, but treatment hastens improvement. Rickettsiosis can also be due to infection with R. parkeri, R. amblyommii, and Rickettsia species 364D (also called R. philipii). Isolation of SFG Rickettsiae is rare in clinical practice due to the difficulty of obtaining culture; consequently, serology, immunologic detection from tissue, and PCR are more often used for diagnosis. Microimmunofluorescent (MIF) antibody tests, enzyme-linked immunosorbent assays (ELISAs), and Western blot immunoassays can be used to detect convalescent IgG and IgM antibodies, but these methods can only be used at least 10-14 days after the onset of illness when antibody concentrations are high enough for detection. McQuiston et al. (2014) concluded that the “use of IgM antibodies should be reconsidered as a basis for diagnosis and public health reporting of RMSF and other spotted fever group rickettsia in the United States” in one small study; the study demonstrated that IgM findings often resulted in false positives for Rock Mountain Spotted Fever and questioned the value of IgM testing (McQuiston et al., 2014). PCR is a very specific technique. PCR using tissue samples has higher specificity than whole blood PCR. Immunologic detection from a tissue biopsy requires the use of special laboratory equipment so it is not as frequently used as either the serologic or PCR detection methods (McClain, 2024c). 

Ehrlichiosis and Anaplasmosis
Human ehrlichiosis was first reported in 1986, and the causative agent for human granulocytic anaplasmosis, Anaplasma phagocytophilum, was identified in 1994. Both ehrlichiosis and anaplasmosis are transmitted from the bite of infected ticks and have similar clinical and laboratory manifestations. Ehrlichiosis can be caused by Ehrlichia chaffeensis, E. ewingii, and E. muris. Typically, patients have a fever within an incubation period of one to two weeks. Other symptoms can include malaise, myalgia, headache, chills, gastrointestinal distress, and cough. Both leukopenia and thrombocytopenia can occur. Diagnosis via culture is extremely difficult. “Until 1995, only two isolates of E. chaffeensis had been recovered from humans; in both cases, this process required over 30 days of cultivation. The isolation of A. phagocytophilum from three additional patients has been accomplished using a cell culture system derived from human promyelocytic leukemia cells (McClain, 2024b). IFA testing for bacteria-specific antibodies is the most common method for diagnosing ehrlichiosis and anaplasmosis, but similar to rickettsiae, ELISA, PCR, and immunochemical tissue staining can be used as well. Unlike rickettsiosis, ehrlichiosis and anaplasmosis can also be detected by the presence of characteristic intraleukocytic morulae in a peripheral blood smear or buffy coat smear (McClain, 2024b).

Borrelia Infections
Besides Lyme disease, caused by Borrelia burgdorferi, Borrelia can cause relapsing fever. Tick-borne relapsing fever (TBRF) in North America is primarily caused by B. hermsii, B. turicatae, B. parkeri, B. miyamotoi, and B. mazzottii, and louse-borne relapsing fever (LBRF) is an infection caused by B. recurrentis (Barbour, 2024; Miller et al., 2024). The characteristic feature of these infections is the relapsing fever due to cyclical spirochetemia caused by antigenic variation of the spirochetes. Each bout of fever lasts three to 12 days with temperatures ranged from 39◦C to 43◦C (102.2◦F to 109.4◦F). Visual analysis by Giemsa or Wright staining blood smears taken during a febrile episode is common practice. PCR can also be used on a variety of samples, including cerebrospinal fluid (CSF), blood, tissue, or even culture medium. According to the CDC, “a change in serology results from negative to positive, or the development of an IgG response in the convalescent sample, is supportive of a TBRF diagnosis” (CDC, 2024p). One exception is using antibodies to the GlpQ protein characteristic of these Borrelia species but not to B. burgdorferi (Lyme disease) (Barbour, 2024).

Protozoa infections
Babesiosis is due to primarily Babesia microti in the U.S, but B. divergens and B. venatorum are the primary causative agents of babesiosis in Europe and China, respectively. The incubation period of Babesia depends on the mode of transfection: one to four weeks following a tick bite; the incubation period after transfusion of contaminated blood products usually or three to seven weeks but ranges from one week to six months. The most common symptoms of infection include a fever, fatigue, malaise, chills, sweats, headache, and myalgia. Immunocompromised individuals can develop relapsing babesiosis due to an absent or impaired production of antibodies with approximately 20% mortality rate for patients who develop relapsing babesiosis. Most patients with babesiosis are also co-infected with other tickborne bacterial pathogens. “Preferred tools for diagnosis of babesiosis include blood smear for identification of Babesia organisms and polymerase chain reaction (PCR) for detection of Babesia DNA. Serology can be a useful adjunct to blood smear and PCR” (Krause & Vannier, 2024). Serology is not ideal in diagnosing an acute infection since antibody concentrations remain elevated post-recovery.

Plasmodium falciparum, P. vivax, and P. ovale are responsible for malaria. They are spread by the bite of an Anopheles mosquito where their sporozoites infect the liver within one to two hours. Within the hepatocyte, they form merozoites. Upon rupturing into the bloodstream, the merozoites infect red blood cells for trophozoite formation, causing the erythrocytic stage of the life-cycle where additional merozoites are released. During this stage of the cycle, the symptoms of malaria, including fever, occur. This process usually takes 12 to 35 days, but clinical manifestations can be delayed in individuals with partial immunity or those who are taking ineffective prophylaxis. Other initial symptoms can include irregular heartbeat, cough, anorexia, gastrointestinal distress, sweating, chills, malaise, arthralgia, and myalgia. Malaria, if left untreated, can also include acidosis, hypoglycemia, severe anemia, renal and hepatic impairment, edema, and death (Cohee & Seydel, 2022). Parasite-based diagnosis may include microscopic examination of blood smears, which can often identify the species of Plasmodium as well as the parasite density, and antigen-based tests. Rapid diagnostic testing (RDT) of the antigens using immunochromatographic methods is available, but the accuracy of the RDT can vary considerably. NAATs can also be used to identify a malarial infection, and NAATs “are typically used as a gold standard in efficacy studies for antimalarial drugs, vaccines, and evaluation of other diagnostic agents” with a “theoretical limit of detection for PCR … estimated at 0.02 to 1 parasite/microL” (Hopkins, 2023). The Mayo Clinic Laboratories indicates that “PCR is an alternative method of malaria diagnosis that allows for sensitive and specific detection of Plasmodium species DNA from peripheral blood. PCR may be more sensitive than conventional microscopy in very low parasitemias, and is more specific for species identification…Malaria PCR can be used in conjunction with traditional blood film or Babesia PCR when the clinical or morphologic differential includes both babesiosis and malaria” Clinic (2024).

Viral infections
Examples of arthropod-borne viruses (arboviruses) include West Nile virus (WNV), dengue, yellow fever virus (YFV), chikungunya, and Colorado tick fever virus. In the United States, WNV is the most common arbovirus reported to the CDC. In 2016, 96% of the reported 2,240 cases of domestic arboviruses were WNV with 61% of the WNV cases reported being neuroinvasive. Neuroinvasive WNV includes meningitis, encephalitis, and acute flaccid paralysis (Burakoff et al., 2018). In general, most infected individuals are asymptomatic with only 20% – 40% of infected patients showing any characteristic symptoms of WNV, including fever, headache, malaise, myalgia, anorexia, and rash. Diagnosis of WNV of a symptomatic individual usually occurs with a WNV IgM antibody capture ELISA (MAC-ELISA) assay. A patient with symptoms of a neurologic infection does require a lumbar puncture. Confirmatory testing can include a plaque reduction neutralization test (PRNT). PCR testing is primarily used with immunocompromised patients who have delayed or absent antibody production, patients with a history of prior flavivirus infections, and blood donors who may be asymptomatic (Petersen, 2022).

Dengue virus (DENV) infection is a result of being bitten by an infected Aedes aegypti or A. albopictus mosquito. Four distinct DENV types of Flavivirus are known: DENV-1, DENV-2, DENV-3, and DENV-4. DENV is endemic throughout much of the tropical regions of the world, but the only region of the U.S. endemic for DENV is Puerto Rico. The last major outbreak occurred in Puerto Rico in 2010 where 26,766 cases of suspected DENV were reported and 47% of all laboratory tested specimen were positive (CDC, 2024f). “Dengue fever … is an acute febrile illness defined by the presence of fever and two or more of the following but not meeting the case definition of dengue hemorrhagic fever: headache, retro-orbital or ocular pain, myalgia and/or bone pain, arthralgia, rash, hemorrhagic manifestations … [and] leukopenia. The cardinal feature of dengue hemorrhagic fever is plasma leakage due to increased vascular permeability as evidenced by hemoconcentration (≥ 20 percent rise in hematocrit above baseline), pleural effusion, or ascites. DHF [dengue hemorrhagic fever] is also characterized by fever, thrombocytopenia, and hemorrhagic manifestations ….” (Thomas et al., 2022). Laboratory diagnostic testing includes direct detection of viral components in serum or indirect serologic assays. “Detection of viral nucleic acid or viral antigen has high specificity but is more labor intensive and costly; serology has lower specificity but is more accessible and less costly” (Thomas et al., 2022). Culture testing as a diagnostic tool usually is time-prohibitive.

Zika virus is a mosquito-borne illness discovered in Uganda in 1947 but has since spread across Asia and to the Americas. Zika infection has been tied to several birth defects. The first human cases of Zika were detected in 1952. Prior to 2007, at least 14 cases of Zika had been documented. Symptoms of Zika are similar to those of many other diseases; therefore, many cases may not have been recognized (CDC, 2024t). The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (CDC, 2024t). The illness is usually mild with symptoms beginning two to seven days after being bitten by an infected mosquito, lasting for several days to a week. Most individuals infected with Zika virus are unaware of the infection, as only a maximum of 25% of people infected will exhibit symptoms (CDC, 2024t; LeBeaud, 2023). Diagnosis of the Zika virus is definitively established through reverse-transcription polymerase chain reaction (RT-PCR) for Zika virus RNA in all symptomatic patients. Aside from pregnant individuals who have traveled to an at risk area, asymptomatic patients are typically not tested (LeBeaud, 2023).

Colorado tick fever virus (CTFV) is a Reoviridae transmitted primarily by the Rocky Mountain wood tick (Dermacentor andersoni) in the western U.S. and Canada. Transmission of CTFV has also been reported in blood transfusions. The incubation period can last up to 14 days, and symptoms include fever, headache, chills, myalgia, leukopenia, and prostration. Only 15% of symptomatic patients demonstrate a rash. Serologic tests are usually not helpful until at least 10-14 days for antibody production whereas real-time PCR (RT-PCR) can be used on the first day of symptoms (Petersen, 2021).

Yellow fever, occurring primarily in sub-Saharan Africa and South America, is a flavivirus spread by mosquitoes that causes hemorrhagic fever with a high fatality rate. An outbreak in Brazil in January-March 2018 resulted in four of ten patients infected with YFV dying. None of those showing symptoms had been vaccinated against YFV. Yellow fever causes hemorrhagic diathesis due to decreased synthesis of vitamin K-dependent coagulation factors as well as hepatic dysfunction, renal failure, and coagulopathy. Yellow fever diagnosis is typically made by a serologic test using an ELISA-IgM assay; however, this assay does cross-react with other flaviviruses and with the YFV vaccination. Rapid diagnostic testing using either PCR or immunoassay is available. Viral isolation and culture can be performed, but it requires inoculation of mosquitoes or mammalian cell culture. Tissue biopsy, such as liver, cannot be performed on the living patient due to possible fatal hemorrhaging; biopsy would be performed during the post-mortem workup (Wilder-Smith, 2024).

Chikungunya virus, endemic in many tropical and subtropical regions of the world, is transmitted by the mosquitoes Aedes aegypti and Aedes albopictus. Within the U.S., chikungunya is prevalent in Puerto Rico where approximately 25% of blood donors were seropositive; it has also been reported in Florida. Both dengue and Zika are transmitted by the same vectors, so these viruses often co-circulate geographically Chikungunya can cause acute febrile polyarthralgia and arthritis. The predominant testing method for diagnosis of chikungunya is the detection of viral RNA via either RT-PCR or virus serology using either ELISA or IFA. Viral culture is typically not used as a diagnostic tool but is used for epidemiologic research (Wilson & Lenschow, 2022).

Types of Testing