May has arrived, and for the majority of your patients it signals the end of the school year and the beginning of summer vacation. Zika virus is on the minds of most people since its arrival to the Western Hemisphere in March 2015. With the fluidity of this outbreak and almost daily news updates and recommendations, many parents have voiced or will be voicing concerns regarding summer travel destinations.
Many concerns about Zika virus have been previously addressed in this column (“Zika virus: More questions than answers?” by Dr. Kristina Bryant). However, if the decision is to avoid international travel because of the ongoing Zika outbreak, it doesn’t mean your patients get a free pass and will not have to be concerned about acquiring any infectious diseases. They still need to be vigilant about avoiding those pesky vectors that transmit arboviruses and other vector-borne diseases that occur in the United States.
Dr. Bonnie M. Word
Arboviruses are transmitted by mosquitoes, ticks, or fleas. Most infections are subclinical. If symptoms develop, they are manifested by a generalized febrile illness including fever, headache, myalgia, arthralgia, and rash. Hemorrhagic fever (dengue) or neuroinvasive disease can include aseptic meningitis, encephalitis, or acute flaccid paralysis. Neuroinvasive disease rarely occurs with dengue, Colorado tick fever, and chikungunya infections.
While more than 100 arboviruses can cause infection, some of the more common arboviruses associated with human disease include West Nile, first detected in the United States in 1999 and chikungunya, first reported in the Americas in 2013 with local transmission documented in Florida, Puerto Rico, and the U.S. Virgin Islands in 2014. It is estimated that dengue causes over 100 million cases worldwide annually. Almost 40% of the world’s inhabitants live in endemic areas. The majority of cases on the U.S. mainland are imported. However, it is endemic in all U.S. territories including Guam, American Samoa, the U.S. Virgin Islands, and Puerto Rico. Between September 2015 and March 2016, Hawaii experienced a dengue outbreak involving 264 individuals including 46 children. As of April 16, 2016, there were no infectious individuals on the island.
Courtesy Wikimedia Commons/Muhammad Mahdi Karim/Creative Commons License
Other domestic arboviruses causing disease include St. Louis, Eastern, and Western Equine encephalitis, La Crosse encephalitis, Colorado tick fever, and Powassan virus. All are transmitted by mosquitoes with the exception of Powassan and Colorado tick fever, which are transmitted by ticks. The numbers of cases nationally are much lower for these diseases, compared with West Nile, dengue, and chikungunya. National and state-specific information is available for domestic arboviruses at diseasemaps.usgs.gov/mapviewer. Data is compiled by ArboNET, a national arboviral surveillance system that is managed by the Centers for Disease Control and Prevention (CDC) in conjunction with state health departments. Not only is human disease monitored, but it also maintains data on viremic blood donors, dead birds, mosquitoes, veterinary disease cases, and sentinel animals.
Spring and summer are the most active seasons for ticks. Bacterial and spirochetal diseases transmitted by them include rickettsial diseases such as Rocky Mountain Spotted Fever, ehrlichiosis, and anaplasmosis. Tularemia in addition to Lyme and tick-borne relapsing fever are also transmitted by ticks. Babesiosis, which is due to a parasite, and southern tick-associated rash illness (STARI), whose causative agent is yet to be determined, are two additional tick-related diagnoses.
Of note, dengue, chikungunya, and Zika are all transmitted by infected Aedes mosquitoes. There is no enzootic cycle. Just human-mosquito-human transmission. In contrast, West Nile virus is transmitted by Culex mosquitoes in an enzootic cycle between an avian reservoir and humans.
Treatment
There is no specific treatment for arboviral infections. The primary goal is relief of symptoms with fluids, bed rest, and analgesics. For bacterial vector-borne diseases, antibiotic therapy is indicated and is based on the specific pathogen. Doxycycline is the drug of choice for treatment of suspected and confirmed Rocky Mountain Spotted Fever, ehrlichiosis, and anaplasmosis even in children less than 8 years of age. Delay in initiation of antimicrobial therapy pending definitive diagnosis may lead to an adverse outcome. It is also the drug of choice for tick-borne relapsing fever.
Lyme disease is also responsive to antibiotic treatment. Therapy is based on the disease category. (Lyme disease in “Red Book: 2015 Report of the Committee on Infectious Diseases,” [Elk Grove Village, Ill.: American Academy of Pediatrics, 2015, pp. 516-25]).
STARI clinically presents with a lesion that resembles erythema migrans in southern and southeastern states. However, it has not been associated with any of the complications reported with disseminated Lyme disease. Treatment is not recommended.