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Objectives This review article summarizes what has been published on Alkhumra hemorrhagic fever virus (AHFV), a novel flavivirus that was discovered in Saudi Arabia in 1995. Methods PubMed was used to search for studies published from January 1995 to June 2019 using the key words Alkhumra virus, Alkhurma virus, novel flavivirus, and tick-borne encephalitis virus. Additionally, records of the Saudi Ministry of Health were reviewed. Results Thirty-two articles on AHFV were identified. Acute febrile flu-like illness, hepatitis, hemorrhagic manifestations, and, less commonly, encephalitis are the main clinical features. The virus seems to be transmitted from livestock animals to humans by direct contact with these animals or their raw meat, or perhaps by tick or mosquito bites. The ability of ticks and mosquitoes to serve as vectors for AHFV needs to be confirmed by biological studies. The exact role of animals such as sheep, goats, camels, and other mammals in the transmission and maintenance of the virus remains to be elucidated. Preventive measures require an interdisciplinary approach involving the human and veterinary health sectors, the municipality, the ministry of agriculture, the vector control sector, and academic and research institutes. Conclusions AHFV has been well characterized; nevertheless, some aspects remain to be elucidated.

At completion of Hajj, the Islamic pilgrimage to Makkah, pilgrims give thanks for the blessing, and acceptance, of Hajj, marking the end of the pilgrimage by sacrificing an animal and distributing the sacrificial meat to the poor. With over two million Muslims making Hajj, each Hajj, more than 1.2 million heads of cattle: sheep, goats and camels are slaughtered. Over 16 000 abattoir workers work around the clock to sacrifice and process the cattle in keeping with Islamic law and public health guidelines. Because of their proximity to high densities of cattle and cattle meat, Makkah's abattoir workers are at risk of zoonosis. This was a longitudinal study aimed at determining the risk of some zoonotic diseases among male permanent abattoir workers during Hajj. Specifically, seroprevalence of antigens for Brucella, Crimean–Congo haemorrhagic fever (CCHF), Alkhurma haemorrhagic fever (AHF) and Rift Valley Fever (RVF) were determined, among the study participants. An enrolment questionnaire, and a follow‐up questionnaire, with provision of 10 mL blood for testing 2 days before intense Hajj animal exposure, up to 20 days after intense animal exposure and between 30 and 42 days after Hajj butchering exposures. While working with livestock, study participants were interrogated on hand hygiene and personal protection. Eighty male permanent abattoir workers participated in the study. Majority, 96.25% (n = 77) declared washing their hands with soap and water, most 98.75% (n = 79) never used eye protection, few occupational workers dressed in personal protective clothing or footwear. All workers tested negative for CCHF and RVF, one was positive for AHF and six for Brucella. The risk of some zoonotic infections like Brucella and AHF is low among permanent occupational workers in the slaughtering house in Makkah during Hajj 2013. No serological evidence for CCHF and RVF viruses, even though workers showed low compliance with use of personnel protective equipment.

A comprehensive understanding of the geographic distribution of the tick-borne encephalitis virus (TBEV) complex is necessary due to increasing transboundary movement and cross-reactivity of serological tests. This review was conducted to identify the geographic distribution of the TBEV complex, including TBE virus, Alkhurma haemorrhagic fever virus, Kyasanur forest disease virus, louping-ill virus, Omsk haemorrhagic fever virus, and Powassan virus. Published reports were identified using PubMed, EMBASE, and the Cochrane library. In addition to TBEV complex case-related studies, seroprevalence studies were also retrieved to assess the risk of TBEV complex infection. Among 1406 search results, 314 articles met the inclusion criteria. The following countries, which are known to TBEV epidemic region, had conducted national surveillance studies: Austria, China, Czech, Denmark, Estonia, Finland, Germany, Hungary, Italy, Latvia, Norway, Poland, Romania, Russia, Switzerland, Sweden, Slovenia, and Slovakia. There were also studies/reports on human TBEV infection from Belarus, Bulgaria, Croatia, France, Japan, Kyrgyzstan, Netherland, and Turkey. Seroprevalence studies were found in some areas far from the TBEV belt, specifically Malaysia, Comoros, Djibouti, and Kenya. Kyasanur forest disease virus was reported in southwestern India and Yunnan of China, the Powassan virus in the United States, Canada, and east Siberia, Alkhurma haemorrhagic fever virus in Saudi Arabia and east Egypt, and Louping-ill virus in the United Kingdom, Ireland, and east Siberia. In some areas, the distribution of the TBEV complex overlaps with that of other viruses, and caution is recommended during serologic diagnosis. The geographic distribution of the TBEV complex appears to be wide and overlap of the TBE virus complex with other viruses was observed in some areas. Knowledge of the geographical distribution of the TBEV complex could help avoid cross-reactivity during the serologic diagnosis of these viruses. Surveillance studies can implement effective control measures according to the distribution pattern of these viruses.

[Figure][1] PHOTO: ZIAD MEMISH For 5 days, starting 19 August, Saudi Arabia will host the Hajj, the world's largest annual religious pilgrimage, where people from over 180 countries will converge on Mecca. Infectious disease transmission associated with this mass transnational movement of people is well known—malaria in 632 CE, meningitis in 1987 and 2000, polio in 2004, and pandemic influenza in 2009. As the former Deputy Minister of Public Health for Saudi Arabia, I know how immense the challenge is to ensure that the country is prepared to contain the spread of infectious disease and maintain public well-being during this event. Although major progress has been made over the past 30 years in Saudi Arabia and in pilgrimage countries, there is still much more to do to avoid a health catastrophe, given that the pilgrim quota may grow to 2.2 million by 2020. ![Figure][1] PHOTO: BANDAR AL-DANDANI/AFP/GETTY IMAGES Nearly half of Hajj pilgrims are 56 years of age or older, and about half have preexisting health conditions. Many pilgrims originate from countries with low income (66%) or that are involved in conflict (18%), with suboptimal health care, disease surveillance, or prevention education. These factors allow outbreaks to go undetected before reaching epidemic thresholds, and Hajj pilgrims can become unsuspecting disease carriers. The intense and exhausting nature of the rituals, extreme desert temperatures, proximity between pilgrims during congregation and prayers, and commitment to share facilities all collectively create an ideal environment for infectious disease transmission. This year's Hajj will be held in the shadows of recently documented outbreaks of cholera, Ebola virus disease, polio, Middle East respiratory syndrome, measles, meningitis, diphtheria, Lassa hemorrhagic fever, yellow fever, hepatitis, and Nipah virus infection across the countries of pilgrim origin. Hepatitis virus infections and tuberculosis are endemic in many of the pilgrims' home countries. Alkhurma virus is endemic in Saudi Arabia. Potential for zoonotic disease transmission exists through the animal sacrifice rituals, including of imported livestock. Yet only three of these conditions require mandatory vaccination as an entry requirement for participation in the Hajj (meningococcal meningitis, polio, and yellow fever). In 2009, when the H1N1 influenza pandemic coincided with the Hajj, Saudi Arabia convened stakeholders to create a discipline called “mass gathering medicine.” Saudi Arabia strengthened real-time Hajj surveillance and set up a reporting system and emergency operations center to monitor pilgrim safety and infectious disease events. However, if diseases of high transmission potential and case fatality such as Nipah virus or Ebola virus should emerge at the Hajj, Saudi Arabia's response capacities may not be sufficient to stall their impact. Surveillance at entry and exit points could quickly improve disease detection. Likewise, travel services could ensure compliance with international health regulations at all departure and arrival ports. The Hajj pilgrim venues and home country preparatory venues could actually become one-stop points for multiple disease surveillance and education for prevention. It will also be important to create a stockpile of medicines and vaccines in the event of a disease outbreak. Such an endeavor will require investment by the World Health Organization and a multinational strategy that is coordinated by the Saudi Ministry of Health. Performing the Hajj is a deeply emotional wish of all Muslims, and many pilgrims save their lifelong earnings to participate. Thus, restrictions on participating in Hajj to reduce the risk of disease spread is a geopolitical challenge for governments. Vision 2030 is a national development initiative of Saudi Arabia that aims to support the expected growth in the international Hajj pilgrimage, which may reach 4.5 million by 2030. The initiative should involve pilgrim countries and international stakeholders to develop public health safeguards for mass gatherings, which for many, may be a once-in-a-lifetime event. [1]: pending:yes

In South Asia, Haemaphysalis spinigera tick transmits Kyasanur Forest Disease Virus (KFDV), a flavivirus that causes severe hemorrhagic fever with neurological manifestations such as mental disturbances, severe headache, tremors, and vision deficits in infected human beings with a fatality rate of 3–10%. The disease was first reported in March 1957 from Kyasanur forest of Karnataka (India) from sick and dying monkeys. Since then, between 400 and 500 humans cases per year have been recorded; monkeys and small mammals are common hosts of this virus. KFDV can cause epizootics with high fatality in primates and is a level-4 virus according to the international biosafety rules. The density of tick vectors in a given year correlates with the incidence of human disease. The virus is a positive strand RNA virus and its genome was discovered to code for one polyprotein that is cleaved post-translationally into 3 structural proteins (Capsid protein, Envelope Glycoprotein M and Envelope Glycoprotein E) and 7 non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). KFDV has a high degree of sequence homology with most members of the TBEV serocomplex. Alkhurma virus is a KFDV variant sharing a sequence similarity of 97%. KFDV is classified as a NIAID Category C priority pathogen due to its extreme pathogenicity and lack of US FDA approved vaccines and therapeutics; also, the infectious dose is currently unknown for KFD. In India, formalin-inactivated KFDV vaccine produced in chick embryo fibroblast is being used. Nevertheless, further efforts are required to enhance its long-term efficacy. KFDV remains an understudied virus and there remains a lack of insight into its pathogenesis; moreover, specific treatment to the disease is not available to date. Environmental and climatic factors involved in disseminating Kyasanur Forest Disease are required to be fully explored. There should be a mapping of endemic areas and cross-border veterinary surveillance needs to be developed in high-risk regions. The involvement of both animal and health sector is pivotal for circumscribing the spread of this disease to new areas.

After its first appearance in Alkhumra district of Jeddah in 1994-1995, and then in Makkah in 2001-2003, the new hemorrhagic fever virus, known as Alkhumra (misnamed as Alkhurma) virus (ALKV), has subsequently been reported from Najran, in the south border of Saudi Arabia.This is a descriptive cohort study summarizing the epidemiological, clinical, and laboratory characteristics of ALKV infected patients diagnosed in Najran from 1 August 2003 through 31 December 2009.A total of 148 suspected cases were reported, of which 78 (52.7%) cases were laboratory confirmed; 2 cases in 2003, 1 case in 2004, 4 cases in 2005, 1 case in 2007, 12 cases in 2008, and 58 cases in 2009. The cases were reported year round but 64.1% (50/78) of them occurred in the summer time. Twenty-five (32.1%) cases occurred as clusters in 5 families. The virus seemed to be transmitted from livestock animals to humans by direct contact with these animals and likely by mosquito bites. Ticks did not seem to be involved in the transmission of infection from animals to humans. Clinical and laboratory features included fever (100%), headache (85.9%), malaise (85.9%), arthralgia (83.3%), anorexia (82.1%), myalgia (82.1%), backache (71.8%), nausea and vomiting (71.8%), chills (60.3%), retro-orbital pain (55.1%), diarrhea (51.3%), abdominal pain (48.7%), hemorrhagic manifestations (25.6%), central nervous system manifestations (23.1%), leucopenia (87.7%), elevated liver enzymes (85.7%), prolonged partial thromboplastin time (52.6%), thrombocytopenia (46.2%), elevated creatine kinase level (45.7%), and elevated lactate dehydrogenase (25.0%).ALKV infection has now been recognized outside its original boundaries in Saudi Arabia which may herald its identification in other countries.

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 (1) 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 (2). 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 (3) 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 (4,5). 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.

TOC summary: Infection was associated with tick bites and contact with farm animals., Alkhurma virus is a flavivirus, discovered in 1994 in a person who died of hemorrhagic fever after slaughtering a sheep from the city of Alkhurma, Saudi Arabia. Since then, several cases of Alkhurma hemorrhagic fever (ALKHF), with fatality rates up to 25%, have been documented. From January 1, 2006, through April 1, 2009, active disease surveillance and serologic testing of household contacts identified ALKHF in 28 persons in Najran, Saudi Arabia. For epidemiologic comparison, serologic testing of household and neighborhood controls identified 65 serologically negative persons. Among ALKHF patients, 11 were hospitalized and 17 had subclinical infection. Univariate analysis indicated that the following were associated with Alkhurma virus infection: contact with domestic animals, feeding and slaughtering animals, handling raw meat products, drinking unpasteurized milk, and being bitten by a tick. After multivariate modeling, the following associations remained significant: animal contact, neighboring farms, and tick bites.

Langat virus (LGTV), one of the members of the tick-borne encephalitis virus (TBEV) complex, was firstly isolated from Ixodes granulatus ticks in Malaysia. However, the prevalence of LGTV in ticks in the region remains unknown. Surveillance for LGTV is therefore important and thus a tool for specific detection of LGTV is needed. In the present study, we developed a real-time quantitative reverse-transcription-polymerase chain reaction (qRT-PCR) for rapid detection of LGTV. Our findings showed that the developed qRT-PCR could detect LGTV at a titre as low as 0.1 FFU/ml. The detection limit of the qRT-PCR assay at 95% probability was 0.28 FFU/ml as determined by probit analysis (p ≤ 0.05). Besides, the designed primers and probe did not amplify ORF of the E genes for some closely related and more pathogenic viruses including TBEV, Louping ill virus, Omsk hemorrhagic fever virus (OHFV), Alkhurma virus (ALKV), Kyasanur Forest Disease virus (KFDV) and Powassan virus (POWV) which showed the acceptable specificity of the developed assay. The sensitivity of the developed method also has been confirmed by determining the LGTV in infected tick cell line as well as LGTV- spiked tick tissues.

Tick-borne encephalitis (TBE) is one of the most dangerous human infections occurring in Europe and many parts of Asia. The etiological agent Tick-borne encephalitis virus (TBEV), is a member of the virus genus Flavivirus, of the family Flaviviridae. TBEV is believed to cause at least 11,000 human cases of encephalitis in Russia and about 3000 cases in the rest of Europe annually. Related viruses within the same group, Louping ill virus (LIV), Langat virus (LGTV) and Powassan virus (POWV), also cause human encephalitis but rarely on an epidemic scale. Three other viruses within the same group, Omsk hemorrhagic fever virus (OHFV), Kyasanur Forest disease virus (KFDV) and Alkhurma virus (ALKV), are closely related to the TBEV complex viruses and tend to cause fatal hemorrhagic fevers rather than encephalitis. This review describes the clinical manifestations associated with TBEV infections, the main molecular-biological properties of these viruses, and the different factors that define the incidence and severity of disease. The role of ticks and their local hosts in the emergence of new virus variants with different pathogenic characteristics is also discussed. This review also contains a brief history of vaccination against TBE including trials with live attenuated vaccine and modern tendencies in developing of vaccine virus strains.

A 2009 deployment of military units from several Saudi Arabian provinces to Jazan Province, Saudi Arabia, enabled us to evaluate exposure to Alkhurma, Crimean-Congo, dengue, and Rift Valley hemorrhagic fever viruses. Seroprevalence to all viruses was low; however, Alkhurma virus seroprevalence was higher (1.3%) and less geographically restricted than previously thought.

To date, tick-borne flaviviruses responsible for hemorrhagic fever in humans have been isolated in Siberia (Omsk hemorrhagic fever virus), India (Kyasanur Forest disease virus, KFDV), and in Saudi Arabia (Alkhurma virus, ALKV). Prior to this study, only partial coding sequences of these severe pathogens had been determined. We report here the complete coding sequence of ALK virus, which was determined to be 10,248 nucleotides (nt) long, and to encode a single 3,416 amino acid polyprotein. Independent analyses of the complete polyprotein and the envelope protein provided genetic and phylogenetic evidence that ALKV belongs to the tick-borne flavivirus group, within which it is most closely related to KFDV. Analysis of structural genes, genetic distances, and evolutionary relationship indicate that ALKV and KFDV derived from a common phylogenetic ancestor and constitute two genetic subtypes of the same virus species according to current genetic criteria of classification.

We recently determined that Nanjianyin virus, isolated from serum of a patient in Yunnan Province, China, in 1989, is a type of Kyasanur Forest disease virus. Results of a 1987-1990 seroepidemiologic investigation in Yunnan Province had shown that residents of the Hengduan Mountain region had been infected with Nanjianyin virus.

In the spring of 1957, an outbreak of severe disease was documented in people living near the Kyasanur forest in Karnataka state, India, which also affected wild nonhuman primates. Collection of samples from dead animals and the use of classical virological techniques led to the isolation of a previously unrecognized virus, named Kyasanur forest disease virus (KFDV), which was found to be related to the Russian spring-summer encephalitis (RSSE) complex of tick-borne viruses. Further evaluation found that KFD, which frequently took the form of a hemorrhagic syndrome, differed from most other RSSE virus infections, which were characterized by neurologic disease. Its association with illness in wild primates was also unique. Hemaphysalis spinigera was identified as the probable tick vector. Despite an estimated annual incidence in India of 400–500 cases, KFD is historically understudied. Most of what is known about the disease comes from studies in the late 1950s and early 1960s by the Virus Research Center in Pune, India and their collaborators at the Rockefeller Foundation. A report in ProMED in early 2012 indicated that the number of cases of KFD this year is possibly the largest since 2005, reminding us that there are significant gaps in our knowledge of the disease, including many aspects of its pathogenesis, the host response to infection and potential therapeutic options. A vaccine is currently in use in India, but efforts could be made to improve its long-term efficacy.

identity to the prototype strain. Alzahrani et al. [2] quote the paper by Zaki [5] . From this paper, however, it is not possible to obtain information on where the index patient came from. While both names can probably be justified, it should be the discoverer who has the right to name a virus. The debate should come to an end once the ICTV has made its statement. Another issue is that apparently errors have occurred in a prior publication [3] . Madani et al. question the conclusion of Alzahrani et al. ticks being the vector. While the figures provided in the two publications are clearly not congruent, the medical history put together retrospectively may or may not be entirely correct. Anyway, a conclusion from the mere number of cases as to the vector of the virus is probably not possible. There is an ongoing discussion on the transmission of Alkhumra sive Alkhurma virus. As it is a member of the TBE group of flaviviruses, it appears conceivable that it may be preferentially transmitted by ticks. In this line is the isolation of Alkhumra sive Alkhurma virus from ticks [6] . However, the epidemiological patterns put forward suggest a possible role of mosquitoes as vectors [7] . This issue should be solved by vector transmission studies in vitro and by isolation of the virus in nature. Therefore, either statement is at present speculative. Intervirology has decided to publish the ensuing letter by Madani et al. [1] and a response by Alzahrani et al. [2] concerning a prior publication [3] . As the letter by Madani et al. was obviously not accepted by EID, Intervirology feels that it is fair and appropriate to provide the authors the opportunity to discuss what they see as substantial errors in the work of Alzahrani et al. [3] . Taxonomy is apparently a matter that raises emotions. Disagreements between researchers on designation of a new virus have occurred in the past, one only has to remember the issue on HTLV-III versus LAV between renowned groups of researches that was eventually cleared. The virus is now named and unanimously accepted as HIV. Another example is the Sin Nombre hantavirus, which was originally named Four Corners virus and temporarily renamed Muerto Canyon virus. There are no clear rules for the naming of new viruses. For arboviruses it is common use to name the virus according to geographical location, disease or vector (Kyasanur Forest disease virus, West-Nile virus, sandfly virus, tick-borne encephalitis virus, yellow fever virus, Japanese encephalitis virus). In the case of Alkhumra sive Alkhurma virus, the controversy has been ongoing for a while [4] . It should be remembered that not the name of a distinct virus species is disagreed on, but a mere genotype of Kyasanur Forest disease virus with about 89% Published online: March 19, 2012

Evidence for the tickborne nature of Alkhurma hemorrhagic fever virus (AHFV) is indirect because AHFV has not been detected in arthropods. One Ornithodoros savignyi tick from Saudi Arabia contained AHFV RNA. This is the first direct evidence that AHFV is a tickborne flavivirus and confirms the association between human AHFV cases and tickbite history.

Alkhurma virus (ALKV) is a tick-borne class 4 flavivirus responsible for several human cases of haemorrhagic fever in Saudi Arabia, with no specific treatment currently available. The viral RNA encodes a serine protease (NS2B–NS3), essential for virus replication in infected cells, that constitutes an attractive target for antiviral compounds. In an attempt to identify residues and motifs on NS2B that are necessary for protease activity of the ALKV NS2B–NS3 complex, a series of modified NS2B–NS3 proteins was constructed, with point mutations on particular residues or with the NS2B domain derived from two different viruses. Four mutants and the two chimeric proteins exhibited reduction of protease activity against BAPNA (a p-nitroanilide substrate). The results demonstrate that tight complementarity of the protein sequences is necessary for NS2B-dependent activation of NS3. The results also determine residues in the ALKV NS2B cofactor essential for protease activation, giving new insights into protease function in flaviviruses.

A flavivirus related to the tick-borne encephalitis complex was isolated from the blood of 6 male butchers, aged 24-39 years, in Jeddah, Saudi Arabia in November and December 1995. Two of the patients died and the other 4 recovered completely. Four more patients, 3 males and 1 female, were diagnosed serologically by immunoglobulin M capture enzyme-linked immunosorbent assay and seroconversion in acute and convalescent blood samples examined by indirect immunofluorescent test using Vero cells infected with the isolated virus. The virus identity was confirmed at the Centers for Disease Control and Prevention, Fort Collins, Colorado, USA, by the polymerase chain reaction; it was closely related to Kayasanur Forest disease virus. All infected patients had similar clinical and laboratory symptoms and signs, including fever, headache, generalized body aches, arthralgia, anorexia, vomiting, leucopenia, thrombocytopenia, elevated liver enzymes (serum glutamic oxalacetic and serum glutamic pyruvic transaminases), elevated creatinine phosphokinase, and elevated blood urea. One patient developed symptoms of encephalitis, but survived without any sequel. Skin rash developed in 2 patients, morbilliform on the hands, feet, and lower abdomen of one patient and purpuric associated with melaena in the second patient. Eight of the 10 confirmed patients were working with sheep, and the disease may be a zoonotic viral infection.

Objectives Four patients with typical acute viral hemorrhagic fever were identified in the holy city of Makkah, Saudi Arabia, between 8 and 23 February 2001, the Hajj (pilgrimage) period of that year. Tests for Rift Valley fever (RVF), Crimean–Congo hemorrhagic fever (CCHF), and dengue were negative. Blood specimens were sent to the Centres for Disease Control and Prevention (CDC), Atlanta for viral culture and testing for other hemorrhagic fever viruses. A new flavivirus closely related to the tick-borne Kyasanur forest disease virus was isolated. This new flavivirus was originally isolated in 1995 from 6 patients with dengue-like hemorrhagic fever from Alkhumra district, south of Jeddah, Saudi Arabia. Methods A case definition was formulated for surveillance of this new disease in Saudi Arabia. Blood specimens were collected from all patients with suspect ‘Alkhumra’ virus (ALKV) infection and tested for ALKV, RVF, CCHF, dengue, and West Nile encephalitis. Patients data were prospectively collected on standardized data collection forms. Results From 8 February 2001 through 9 February 2003, a total of 37 cases were identified in Makkah, 20 of them were laboratory confirmed. Acute febrile flu-like illness with hepatitis (100%), hemorrhagic manifestations (55%), and encephalitis (20%) were the main clinical features. The case fatality was 25%. The disease seemed to be transmitted from sheep or goat to humans by the mosquito bites or direct contact with these animals. Conclusions ALKV infection is a novel serious zoonotic hemorrhagic fever virus discovered in Saudi Arabia. The role of arthropods such as ticks and mosquitoes, and animals such as sheep, goat, and rodents in the transmission and maintenance of the virus remains to be elucidated.

Alkhurma virus (ALKV) is a recently discovered class-4 flavivirus that was responsible for several cases of severe haemorrhagic fever in humans in Saudi Arabia. It has been shown for other flaviviruses that processing of the viral polyprotein is partly due to the virus-encoded NS2B/NS3 trypsin-like serine protease. As the viral proteinase plays a critical role in the virus replication cycle, it represents one of the main targets for antiviral therapy against members of the Flavivirus genus. We report here on the identification of the ALKV NS2B and NS3 domains and the expression and purification of a catalytically active viral protease as a hexahistidine recombinant protein. Its enzymatic properties were characterized in vitro using a para-nitroanilide substrate. This constitutes the first characterization of the proteinase from a class-4 flavivirus. Our results indicate that the association of NS3 with a short segment of NS2B is necessary and sufficient for protease activity. The developed system could help to identify or design inhibitors potentially active as antiviral drugs against ALKV and other pathogenic flaviviruses.