Alkhurma hemorrhagic fever in travelers returning from Egypt, 2010.

To the Editor: The report of 2 visitors from Italy being infected by Alkhurma hemorrhagic fever virus (AHFV) in southeastern Egypt near the border with Sudan () provides useful data to help clarify the evolutionary origin of these tick-borne flaviviruses. AHFV was first isolated in Saudi Arabia and is associated with camel ticks (). It is a genetically close relative of Kyasanur Forest disease virus, which was first isolated in India in 1957. Following the original isolation of Kyasanur Forest disease virus, there was no clear explanation for its apparent isolation in the Indian forests. Indeed, its subsequent discovery in southern China () suggested that migratory birds might carry the infected ticks to or from that region.

The most likely explanation for these outbreaks of hemorrhagic disease now begins to fit a pattern that can be interpreted in terms of the diseases’ evolutionary origin in Africa. Thousands of animals are annually transported from Africa and other countries to Mecca, Saudi Arabia, to meet the human demand for food and transport during the Hajj. Many of these animals, including camels, are infested with ticks that may carry AHFV and thus provide the source of this human infectious agent. Phylogenetic evidence had previously suggested that the tick-borne encephalitic flavivirus serocomplex originated in Africa and gradually evolved and dispersed across the Northern Hemisphere of the Old World (,). This concept is totally consistent with the discoveries of AHFV in Saudi Arabia and now in southeastern Egypt. Thus, Africa is a likely source of infected ticks that are regularly moved between Africa and Saudi Arabia. This concept of an African evolutionary origin for these viruses could readily be tested by serologic investigation of humans and animals and also by analysis of ticks from this region of Africa.

In Response: The concept suggested by Charrel and Gould () of an African evolutionary origin for these tick-borne flaviviruses and their dispersal across the Northern Hemisphere raises concerns over possible spread of a new potentially dangerous infection outside its country of origin. This awareness should alert physicians in Western countries to pathogens that cause unspecific, unusual, or totally unknown clinical signs. We agree that more research is needed in human and animal health, as well as in entomologic and environmental studies, especially in light of the recent data suggesting a nonexclusive role of ticks as vectors for human infection with Alkhurma virus and the hypothesis of human-to-human transmission ().

Past experience with emerging diseases in travelers (Crimean-Congo hemorrhagic fever, Lassa fever, Marburg hemorrhagic fever) or with autochthonous spread of imported diseases (chikungunya, West Nile virus disease, malaria) indicates a consistent delay in the diagnosis of first or sporadic cases, leading to inappropriate or untimely treatment of some of the patients. To confront the problem of unusual and emerging pathogens, Western countries must invest in evidence-based and integrated strategies of preparedness and response.

First, the frontline physicians’ ability to recognize, diagnose, and treat illnesses caused by unusual pathogens should be improved through training covering rare and tropical diseases. Second, a system of timely information and alerts about threats posed by new infectious diseases should be set up. Third, concentrating clinical samples in virology laboratories with proven experience in detecting emerging pathogens is crucial for comprehensive and rapid differential diagnosis. It must be also remembered that no commercial tests are available for serologic or molecular detection of many rare pathogens or for differential diagnosis. And, finally, laboratory diagnosis is often made difficult by antibody cross-reactivity, as documented in our article ().

For Alkhurma virus, further research is needed in the animal setting because little is known about length and severity of illness, duration of viremia, and modes of animal-to-animal and animal-to-human transmission; we need to better understand the role of vectors to limit the spread of the disease.