Virus Heartland: una nueva y emergente encefalitis transmitida por garrapatas

Heartland virus (HRTV) is a Bunyaviridae, phlebovirus that it has recently emerged as the causative agent of human disease characterized by thrombocytopenia and leukopenia in the United States and China. It seems to be the HRTV has been also reported in China, Japan and Korea. Recently the first fatal case of HRTV disease in an 80-year-old Tennessee resident was reported (1).

Amblyomma americanum and Dermacentor variabilis ticks have been involved as a vector of HRTV in USA. The vertebrates amplification hosts associated with enzootic maintenance of the HRTV have been studied in Missouri. Neutralizing antibodies to HRTV in raccoons (42.6%), horses (17.4%), white-tailed deer (14.3%), dogs (7.7%) and opossums (3.8%) were identified. No antibodies were found in birds. The high seroprevalence associated with local abundance of white-tailed deer and raccoons demonstrated these species may be an amplification hosts. Virus isolation experiments from sera and ticks to detect HRTV virus were unsuccessful (2).

In 2012 in Missouri farms, 56.428 ticks of Amblyomma americanum and Dermacentor variabilis were collected. By using RT-PCR (reverse transcription-polymerase chain reaction), several nymphs pools of A. americanum were positive, 8 pools yielded viable viruses. Sequence data from the nonstructural protein of the small segment demonstrates that tick strains and human strains are very similar, ≥97.6% sequence identity (3).

This was the first study to isolate HRTV from ticks and they seem to be implicating as potential vectors. Amblyomma americanum possible to becomes infected by feeding on viremic hosts during the larval stage, and transmission to humans occurs during the spring and early summer when nymphs are abundant and actively host seeking (3).

A seroprevalence survey performed in Minnesota, USA, tested blood samples from domestic animals to determine antibodies to HRTV. Antibodies against virus nucleoproteins in 10%-18% of samples from cattle, sheep, goats, deer, and elk in Minnesota counties were found (4).

Most patients with HRTV show fever, thrombocytopenia, leukopenia fatigue, anorexia, headache, nausea, myalgia, or arthralgia. A clinically compatible disease have been defined as fever (≥38.0°C), leukopenia (white blood cell count <4.500 cells/mm³; normal range = 4.500–12.000 cells/mm³), and thrombocytopenia (platelet count <150.000/mm³; normal range =150.000–400.000/mm³) without a more probably clinical explanation. Physicians in Colombia and Latin America should recognize Heartland virus testing in patients who show fever, leukopenia, and thrombocytopenia without more likely evidence and who have tested negative for Ehrlichia, Anaplasma and Babesia infection or have not responded to doxycycline therapy (5).

Recently, there was a report of the first fatal case of HRTV disease in an 80-year-old Tennessee resident. The patient was admitted at the clinic with fever, confusion, leukopenia, and thrombocytopenia and developed multiorgan failure and hemorrhage. The patient died on hospital day 15, and autopsy specimens were tested for various pathogens as part of an unexplained death evaluation. HRTV antigens were detected in postmortem spleen and lymph nodes by immunohistochemistry, and HRTV was detected in premortem blood by RT-PCR and the virus was isolated in cell culture (6).

Because HRTV is an emerging virus, laboratory diagnosis is incipient yet, the diagnosis in Colombia and Latin America is extremely difficult. However, detection of viral RNA by RT-PCR on blood or tissue can be carry out, hence a ≥4-fold rise antibody titers by PRNT in acute and convalescent serum specimens can be carry out (5).

Like other viruses, no vaccine or medication is available to prevent or treat Heartland virus disease. Because the virus possible is transmitted through infected ticks or other arthropods, prevention depends on using insect repellents, wearing long sleeves and pants and performing tick checks after spending time outdoors (5).

In Colombia especially in the tropics, there are strong evidence of Amblyomma sp and Dermacentor ticks thus, it is likely that HRTV is circulating. The fatal cases in USA demonstrate that HRTV infection can cause severe disease and death. In Colombia, tick’s population are endemic affecting animals and people, the dissemination of the HRTV in Colombia is likely because the favourable geoclimatic conditions (7).

Finally, tick-borne viruses that cause diseases in humans mainly belong to 3 families: Bunyaviridae, Flaviviridae, and Reoviridae, we actually in Latin America do not know about this vector borne disease, it is necessary to carry out several surveys to establish the prevalence of those viruses in the vectors and humans as well.

Marco González T. M.Sc.

Salim Mattar V. Ph.D.

REFERENCES

1. Bosco-Lauth AM, Panella NA, Root JJ, Gidlewski T, Lash RR, Harmon JR, Burkhalter KL, Godsey MS, Savage HM, Nicholson WL, Komar N, Brault AC. Serological Investigation of Heartland Virus (Bunyaviridae: Phlebovirus) Exposure in Wild and Domestic Animals Adjacent to Human Case Sites in Missouri 2012-2013. Am J Trop Med Hyg. 2015; 92:1163-1167.

2. Bosco-Lauth AM, Panella NA, Root JJ, Gidlewski T, Lash RR, Harmon JR, et al. Serological investigation of heartland virus (Bunyaviridae: Phlebovirus) exposure in wild and domestic animals adjacent to human case sites in Missouri 2012-2013. Am J Trop Med Hyg 2015; 92(6):1163-7. doi: 10.4269/ajtmh.14-0702.

3. Savage HM1, Godsey MS Jr, Lambert A, Panella NA, Burkhalter KL, Harmon JR, et al. First detection of heartland virus (Bunyaviridae: Phlebovirus) from field collected arthropods. Am J Trop Med Hyg. 2013; 89(3):445-52. doi: 10.4269/ajtmh.13-0209.

4. Xing Z, Schefers J, Schwabenlander M, Jiao Y, Liang M, Qi X, et al. Novel bunyavirus in domestic and captive farmed animals, Minnesota, USA. Emerg Infect Dis. 2013; 19(9):1487-9. doi: 10.3201/eid1909.130165.

5. Pastula DM, Turabelidze G, Yates KF, Jones TF, Lambert AJ, Panella AJ. Notes from the field: Heartland virus disease - United States, 2012-2013. MMWR Morb Mortal Wkly Rep. 2014 Mar 28;63(12):270-1.

6. Muehlenbachs A, Fata CR, Lambert AJ, Paddock CD, Velez JO, Blau DM. Heartland virus-associated death in Tennessee. Clin Infect Dis. 2014; 59(6):845-50. doi: 10.1093/cid/ciu434.

7. Miranda J, Portillo A, Oteo JA, Mattar S. Rickettsia sp. Strain Colombianensi (Rickettsiales: Rickettsiaceae): A New Proposed Rickettsia Detected in Amblyomma dissimile (Acari: Ixodidae) From Iguanas and Free-Living Larvae Ticks From Vegetation. J Med Entomol 2012; 49(4):960-965. DOI: http://dx.doi.org/10.1603/ME11195.