Vector-borne diseases are infections that are primarily or exclusively transmitted through an invertebrate, generally insects.1 Some pathogens undergo an obligate stage of their life cycle inside the vector; others use the vector only for transport and inoculation. The most common vector-borne diseases are carried through mosquitoes and ticks. Vector-borne diseases account for 17% of all infections worldwide.1 The main impact of these diseases occurs abroad,1 but they are becoming more common in North America. Table 1 and Table 2 summarize common vector-borne diseases.
WHAT IS NEW ON THIS TOPIC: VECTOR-BORNE DISEASES
All pregnant women with a history of travel to a Zika virus outbreak area are advised to undergo viral testing and fetal ultrasonography.
Men with confirmed Zika virus infection should abstain from sexual intercourse or use condoms for six months after the onset of infection.
Men who have traveled to areas of Zika virus transmission but have no known infection should abstain from sexual intercourse or use condoms for at least six months after departure from the area. [Updated]
Rare nonsexual, person-to-person transmission of Zika virus has been reported.
|Clinical recommendation||Evidence rating||References||Comments|
|Women who are pregnant or potentially pregnant should avoid travel to areas where Zika virus is spreading. If they choose to travel to these areas, mosquito avoidance measures should be taken.||C||20||Although malformation and microcephaly are associated with Zika virus infection, the risk of acquiring an infection when bitten by an infected mosquito and the risk of adverse fetal effects if infected are unknown.|
|Men with confirmed Zika virus infection should abstain from sexual intercourse or use condoms for six months after the onset of infection. Men who have traveled to areas of Zika virus transmission but have no known infection should abstain from sexual intercourse or use condoms for at least six months after departure from the area. [Updated]||C||24||—|
|Doxycycline is the drug of choice for rickettsial infections, even in children younger than eight years.||C||34||Benefit outweighs risk|
|Insect repellents with DEET 20% to 50% are effective for the prevention of many vector-borne diseases. Other agents such as picaridin, IR3535, and oil of lemon eucalyptus also appear to be effective.||C||38||Use in conjunction with physical barriers and other arthropod avoidance measures.|
|Insecticide-impregnated bed nets are effective for the prevention of mosquito-borne disease in endemic areas.||A||39||Significant benefit in decreasing incidence of malaria, a mosquito-borne infection|
|Condition||Pathogen||Vector||Clinical presentation||Diagnosis||Treatment options||Prevention|
|Condition||Pathogen||Vector||Clinical presentation||Diagnosis||Treatment options||Prevention|
Although the potential for importation of vector-borne diseases by travelers has been the focus of attention in recent months, other factors are likely more important in the emergence and reemergence of vector-borne disease in the United States. As a result of widening breeding sites and increased food supplies, vector populations and their distribution have increased. Simultaneously, the range of human residence and recreation has widened, driven by urbanization. The increasing overlap of human and vector habitats has made exposure more likely.2
Emerging Viral Diseases
Currently, West Nile virus, dengue, chikungunya, and Zika virus are of particular importance because of their potential to become significant public health threats.
WEST NILE VIRUS
West Nile virus infection is the most common vector-borne viral disease in the United States, with 2,205 U.S. cases reported in 2014 (predominantly between July and September).3 Symptomatic West Nile virus infection is usually a self-limited, nonspecific, flulike febrile illness, although a maculopapular eruption with defervescence is typical.3 The neuroinvasive form occurs in one out of 30 to 70 cases. This form has a fatality rate of approximately 5% to 10% and may lead to flaccid paralysis, typically with meningoencephalitis.3 Extrapyramidal symptoms can occur with West Nile encephalitis. Flaccid paralysis is asymmetric and can involve facial and respiratory muscles. Guillain-Barré syndrome and other neuropathies have also been associated with West Nile virus. Neuroinvasive infection can be diagnosed by detecting West Nile virus–specific immunoglobulin M (IgM) antibodies in the serum of cerebrospinal fluid. However, cross-reactivity with related Flaviviridae, such as dengue, can occur, and antibodies may not be present in the first week of illness. Treatment is supportive.3,4
Although unknown before the mid–20th century, dengue is the most common vector-borne viral disease in the world.5 Before 2009, only a few sporadic, imported cases had been reported in the United States. Since then, it has consistently been a U.S. public health concern, with 837 cases reported in 2013.6 Most of these were travel related, but outbreaks of local transmission have occurred in Texas and Florida. Most recently in 2015, an outbreak occurred on Hawaii Island.7 Dengue is now endemic in Puerto Rico.
Like West Nile virus infection, dengue presents abruptly as a flulike febrile illness, but with myalgias and arthralgias so severe the disease is also known as breakbone fever. The characteristic rash of dengue is erythematous and confluent with patches of unaffected skin, occurring mainly on the limbs. Petechiae sometimes can be seen at sites of compression, such as with blood pressure cuffs or tourniquets. Thrombocytopenia is also characteristic. In patients who have previously been infected with any of the other four serovariants of the virus, dengue hemorrhagic fever or dengue shock syndrome can arise after resolution of the initial febrile illness. This is characterized by capillary leak syndrome and a severe bleeding diathesis, and is uncommon in the United States. Dengue is rarely associated with neurologic complications.
Dengue can be diagnosed through a blood test showing IgM antibodies to dengue virus. However, cross-reactivity with related viruses can produce false-positive results. Treatment is supportive, although aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) should be avoided because of the potential for worsened bleeding and Reye syndrome.
Although not phylogenetically related to dengue, chikungunya is a similar disease producing flulike febrile illness often associated with a maculopapular rash and distinctively disabling arthralgias. Compared with dengue, chikungunya is less likely to cause constitutional symptoms (fever is occasionally absent), leukopenia, and thrombocytopenia, and is more likely to involve small joints (e.g., ankles, wrists, interphalangeal joints).10 Bleeding is rare with chikungunya. Ocular complications may occur, and meningoencephalitis is possible in children. Chikungunya can be diagnosed by detecting IgM antibodies to the virus in blood; however, antibodies may be undetectable in the first two weeks of infection. Treatment is supportive; it is wise to avoid aspirin and NSAIDs until dengue has been excluded. Corticosteroids, NSAIDs, and, in refractory cases, chloroquine (Aralen) and hydroxychloroquine (Plaquenil) have been recommended to treat the chronic arthritis that can be a sequela of the acute illness.11
Zika virus infection, like dengue and chikungunya, spreads rapidly. Zika virus was initially reported in Oceania. An outbreak occurred in Brazil in May 2015, and the virus has since been identified throughout the Americas.12 It is carried by Aedes species mosquitoes, including both Aedes aegypti and Aedes albopictus, the latter of which has a wider range in the United States. [corrected] This suggests a significant potential for spread once it is introduced in this country. In July 2016, local mosquito-borne transmission was confirmed in the United States.13 Zika virus mosquito-borne transmission is endemic in the U.S. territories of Puerto Rico, the Virgin Islands, and American Samoa. Other current endemic regions include the rest of the Caribbean, Mexico, Central and South America (except Chile and Uruguay), Papua New Guinea and several islands in Oceania, and the Cape Verde Islands off the west African coast.14,15
Symptoms of Zika virus infection are similar to those of dengue, but generally less debilitating. Like West Nile virus infection, Zika virus infection is associated with Guillain-Barré syndrome.16
Infection in pregnant women increases the risk of structural brain abnormalities in the fetus, including microcephaly 17,18; this risk may be lower if infection occurs in the third trimester.19 Women who are pregnant or potentially pregnant should avoid travel to areas in which Zika is spreading. If they choose to travel to these areas, mosquito avoidance measures should be taken.20 All pregnant women who have traveled to areas of Zika transmission are advised to undergo testing for Zika virus infection and fetal ultrasonography.21
Unusual among arboviruses, Zika virus appears to be sexually transmitted by infected men to male and female sex partners.22,23 For this reason, men with confirmed infection should abstain from sexual intercourse or use condoms for six months after the onset of infection. Men who have traveled to areas of Zika virus transmission should take similar precautions for at least six months after departure from the area.24 [Updated] Suspected female-to-male sexual transmission and a case of nonsexual person-to-person transmission have also been reported.25,26
Although diagnosis can be made with the detection of IgM antibodies to Zika virus, this method is hampered by extremely limited testing facilities and cross-reactivity with related viruses (such as dengue). The Centers for Disease Control and Prevention (CDC) recommends using real-time reverse transcriptase polymerase chain reaction testing of urine if symptoms began less than 14 days earlier. Testing of serum is also recommended in the first week of the illness.27 However, because real-time reverse transcriptase polymerase chain reaction testing might be falsely negative if the viremia has waned, serum IgM antibody testing for Zika and dengue viruses is recommended in the person with suspected Zika infection.28
Ehrlichiosis presents as a nonspecific syndrome of fever, headache, malaise, and myalgias.29 A rash occurs in 30% of adults and 60% of children. Leukopenia and thrombocytopenia are common.30 Most cases occur in the south-central and southeastern United States.29 Ehrlichiosis incidence increased by fourfold from 2000 to 2008, but decreased between 2008 and 2010.29 The latest national surveillance data show an increased fatality rate in children younger than five years.31 Physician hesitancy to prescribe doxycycline to children younger than eight years is a significant barrier to effective treatment. The CDC and the American Academy of Pediatrics recommend doxycycline for treatment of presumed or confirmed ehrlichiosis regardless of age.29 There is a low risk of tooth staining from limited courses of doxycycline, and treatment with other antibiotics leads to higher fatality rates.31
Spotted fever Rickettsia infections are transmitted by fleas, mites, and ticks. These infections range from mild to life threatening. In the United States, 13,599 cases of spotted fever rickettsiosis were reported from 2008 to 2012.31 Rocky Mountain spotted fever has the highest fatality rate of rickettsial infections (4% with antibiotics and up to 20% to 25% without antibiotics).32 The most common life-threatening complications include meningitis, encephalitis, renal failure, and acute respiratory distress syndrome; the median time from onset of symptoms to death is seven days.31 The fatality rate is higher in children than in older populations.32 Rocky Mountain spotted fever is primarily a clinical diagnosis, with the presence of fever, headache, myalgias, petechial rash, tick exposure, and sometimes eschar.33 Doxycycline should be initiated promptly in suspected cases of rickettsial infection, even in children younger than eight years.34
Other Vector-Borne Diseases
Because curative therapies for vector-borne diseases are limited, prevention is an important focus. Patients should be counseled on minimizing their risk, generally via vector avoidance. The risk of transmission of mosquito-borne diseases is generally highest from dusk to dawn. However, A.edes species mosquitoes feed day and night, and most ticks are daytime feeders. [corrected]
An effective strategy against most insect bites is consistent use of insecticides (permethrin 0.5%) and repellents (diethyltoluamide [DEET] 20% to 50%, picaridin, IR3535, oil of lemon eucalyptus).38 Barriers, such as long-sleeved shirts and long pants, well-screened windows, and insecticide-impregnated bed nets,39 are essential components to insect avoidance.
Data Sources: In addition to a literature search of PubMed, we searched Essential Evidence Plus, the American Academy of Family Physicians, the World Health Organization website, and the CDC website using the term vector-borne disease and individual names of the diseases included in this article. Search dates: December 2015 through July 2016.