Felicity J. Burt

Chikungunya: a re-emerging virus

In the past decade, chikungunya--a virus transmitted by Aedes spp mosquitoes--has re-emerged in Africa, southern and southeastern Asia, and the Indian Ocean Islands as the cause of large outbreaks of human disease. The disease is characterised by fever, headache, myalgia, rash, and both acute and persistent arthralgia. The disease can cause severe morbidity and, since 2005, fatality. The virus is endemic to tropical regions, but the spread of Aedes albopictus into Europe and the Americas coupled with high viraemia in infected travellers returning from endemic areas increases the risk that this virus could establish itself in new endemic regions. This Seminar focuses on the re-emergence of this disease, the clinical manifestations, pathogenesis of virus-induced arthralgia, diagnostic techniques, and various treatment modalities.

Phylogenetic Relationships of Southern African West Nile Virus Isolates

Phylogenetic relationships were examined for 29 southern African West Nile virus (formal name West Nile virus [WNV]) isolates from various sources in four countries from 1958 to 2001. In addition sequence data were retrieved from GenBank for another 23 WNV isolates and Kunjin and Japanese encephalitis viruses. All isolates belonged to two lineages. Lineage 1 isolates were from central and North Africa, Europe, Israel, and North America; lineage 2 isolates were from central and southern Africa and Madagascar. No strict correlation existed between grouping and source of virus isolate, pathogenicity, geographic distribution, or year of isolation. Some southern African isolates have been associated with encephalitis in a human, a horse, and a dog and with fatal hepatitis in a human and death of an ostrich chick.

IgG-sandwich and IgM-capture enzyme-linked immunosorbent assay for the detection of antibody to Rift Valley fever virus in domestic ruminants

The recent occurrence of the first confirmed outbreaks of Rift Valley fever in humans and livestock outside the African region, namely in the Kingdom of Saudi Arabia and Yemen, is of global medical and veterinary concern. Disadvantages of classical techniques for serological diagnosis of Rift Valley fever include health risk to laboratory personnel, restrictions for their use outside endemic areas and inability to distinguish between different classes of immunoglobulins. We report on the development and validation of sandwich and capture ELISAs (both based on inactivated antigen) for detection of IgG and IgM antibody to Rift Valley fever virus in bovine, caprine and ovine sera. Compared to virus neutralisation and haemagglutination-inhibition tests, the IgG sandwich ELISA was more sensitive in detection of the earliest immunological responses to infection or vaccination with Rift Valley fever virus. Its sensitivity and specificity derived from field data sets ranged in different ruminant species from 99.05 to 100% and from 99.1 to 99.9%, respectively. The specificity of IgM-capture ELISA varied between different species from 97.4 to 99.4%; its sensitivity was 100% in sheep tested 5-42 days post-infection. Our results in field-collected, experimental and post-vaccination sera demonstrate that these assays will be useful for epidemiological surveillance and control programmes, import/export veterinary certification, early diagnosis of infection, and for monitoring of immune response in vaccinated animals. As highly accurate and safe tests, they have the potential to replace traditional diagnostic methods, which pose biohazard risks limiting their use outside of endemic areas to high containment facilities.

Molecular evolution of viruses of the family Filoviridae based on 97 whole genome sequences

ABSTRACT Viruses in the Ebolavirus and Marburgvirus genera (family Filoviridae) have been associated with large outbreaks of hemorrhagic fever in human and nonhuman primates. The first documented cases occurred in primates over 45 years ago, but the amount of virus genetic diversity detected within bat populations, which have recently been identified as potential reservoir hosts, suggests that the filoviruses are much older. Here, detailed Bayesian coalescent phylogenetic analyses are performed on 97 whole-genome sequences, 55 of which are newly reported, to comprehensively examine molecular evolutionary rates and estimate dates of common ancestry for viruses within the family Filoviridae. Molecular evolutionary rates for viruses belonging to different species range from 0.46 × 10−4 nucleotide substitutions/site/year for Sudan ebolavirus to 8.21 × 10−4 nucleotide substitutions/site/year for Reston ebolavirus. Most recent common ancestry can be traced back only within the last 50 years for Reston ebolavirus and Zaire ebolavirus species and suggests that viruses within these species may have undergone recent genetic bottlenecks. Viruses within Marburg marburgvirus and Sudan ebolavirus species can be traced back further and share most recent common ancestors approximately 700 and 850 years before the present, respectively. Examination of the whole family suggests that members of the Filoviridae, including the recently described Lloviu virus, shared a most recent common ancestor approximately 10,000 years ago. These data will be valuable for understanding the evolution of filoviruses in the context of natural history as new reservoir hosts are identified and, further, for determining mechanisms of emergence, pathogenicity, and the ongoing threat to public health.

Serodiagnosis of Crimean-Congo haemorrhagic fever.

Several methods for demonstrating antibody to Crimean-Congo haemorrhagic fever virus were compared on serum samples taken from 101 patients during the acute stage of illness and at intervals for up to 59 months thereafter, with emphasis on early detection of the immune response. The deaths of 23 patients on days 5-14 of illness were ascribed to the effects of the disease; two patients died later from other causes. Very few of the patients who died from the acute illness mounted an antibody response detectable by the methods tested. Four patients who died and 18 who recovered were treated with immune plasma collected from recovered patients. Treated patients acquired IgG antibody from the plasma, but it was possible to discern the onset of an endogenous IgM response in those individuals who survived the disease by all of the methods tested. Indirect immunofluorescence (IF) tests detected IgM and/or IgG antibodies at the earliest on day 4 of illness in about 10% of patients who survived the disease, and by day 9 all survivors had antibodies demonstrable by IF. A biotin-streptavidin IF technique offered no advantage over the standard IF test for the early detection of IgG antibody, but demonstrated higher antibody titres and detected IgM antibody earlier in about a quarter of the patients tested. An IgM-capture enzyme-linked immunoassay (ELISA) and an IgG sandwich ELISA demonstrated higher antibody titres than did IF tests, and detected antibody responses at an earlier stage of infection than did IF tests in about one-fifth of patients, but the reverse was true in a similar proportion of instances. A competition ELISA, which detected total antibody activity, produced lower titres than did the IgM and IgG ELISAs, but yielded results which were in close agreement with the findings in IF tests. It was concluded that the IF tests were most convenient for use in making a rapid serodiagnosis of the disease.

An alphavirus replicon-derived candidate vaccine against Rift Valley fever virus.

Rift Valley fever virus (RVFV) is a mosquito-transmitted bunyavirus (genus Phlebovirus) associated with severe disease in livestock and fatal encephalitis or haemorrhagic fever in a proportion of infected humans. Although live attenuated and inactivated vaccines have been used in livestock, and on a limited scale in humans, there is a need for improved anti-RVFV vaccines. Towards this goal, Sindbis virus replicon vectors expressing the RVFV Gn and Gc glycoproteins, as well as the non-structural nsM protein, were constructed and evaluated for their ability to induce protective immune responses against RVFV. These replicon vectors were shown to produce the RVFV glycoproteins to high levels in vitro and to induce systemic anti-RVFV antibody responses in immunized mice, as determined by RVFV-specific ELISA, fluorescent antibody tests, and demonstration of a neutralizing antibody response. Replicon vaccination also provided 100% protection against lethal RVFV challenge by either the intraperitoneal or intranasal route. Furthermore, preliminary results indicate that the replicon vectors elicit RVFV-specific neutralizing antibody responses in vaccinated sheep. These results suggest that alphavirus-based replicon vectors can induce protective immunity against RVFV, and that this approach merits further investigation into its potential utility as a RVFV vaccine.

First documentation of human Crimean-Congo hemorrhagic fever, Kenya.

To the Editor: On October 21, 2000, a previously healthy 25-year-old male farmer was admitted to a mission hospital in western Kenya with an acute hemorrhagic illness. Four days before admission, the patient had rapid onset of fever, headache, nausea, vomiting, severe muscle pains, and diarrhea, which became bloody. On admission his temperature was 36.4°C, pulse was 60/minute, respiratory rate was 20/minute, and blood pressure was 90/40 mm Hg. In addition to the signs and symptoms listed above, the only other abnormal finding on admission was neck stiffness. The differential diagnoses included bacterial dysentery and meningitis. Results of a blood smear for malaria parasites and Widal test for typhoid were negative, and cerebrospinal fluid and urine examinations were normal. The patient was treated with doxycycline, cotrimoxazole, metronidazole, and intravenous fluids. On the day after admission, the patient’s vomitus became blood stained and blood was passed rectally. The patient was isolated and strict barrier nursing implemented on the suspicion of viral hemorrhagic fever (VHF). Progressive hypotension developed, resistant to resuscitation efforts with intravenous fluids and corticosteroids, and later massive bleeding from the nose, mouth, and upper and lower gastrointestinal tract occurred. The patient died on the second day of admission, 6 days after onset of illness. A serum sample was sent to the Arbovirus and Viral Hemorrhagic Fever Reference Laboratory in Nairobi for diagnostic screening. Serologic tests in Nairobi were negative for yellow fever, dengue, West Nile, Chikungunya, and Rift Valley fever (immunoglobulin [Ig] M–capture enzyme-linked immunosorbent assay) and reverse transcriptase-polymerase chain reaction (RT-PCR) tests for flaviviruses, alphaviruses, and Bunyamwera serogroup bunyaviruses were also negative. RT-PCR for Crimean-Congo hemorrhagic fever virus (C-CHFV) was positive. Tests for anti-C-CHFV–specific IgM antibody by indirect immunofluorescence were negative. Virus isolation attempts were then terminated because the cultivation of C-CHFV (the presumptive cause) requires biosafety level 4 facilities. The specimen was submitted to the Special Pathogens Unit in Johannesburg for confirmation of the result. The sample was positive by RT-PCR for C-CHFV and was IgM and IgG antibody negative. No isolation of the virus could be made from the serum sample, possibly because it was received by the Johannesburg laboratory 8 days after initial collection and following freeze-thaw conditions. The specimen was was insufficient to attempt C-CHVF antigen detection assays. Sequencing of the RT-PCR amplicon confirmed C-CHFV. C-CHFV is a tick-borne virus of the genus Nairovirus, family Bunyaviridae, and is widely distributed throughout eastern Europe and the Crimea, to the Middle East and western China, Pakistan, and Africa. Natural hosts for this virus are varied (including wild and domestic animals and birds) and may reflect the feeding preferences of the host tick (1). While C-CHFV infections are rare in humans, the virus is notorious for nosocomial outbreaks of VHF, typically following admission of an index case to a health-care facility where VHF was not suspected, with mortality rates up to 40%. Previous evidence for C-CHFV in Kenya is limited and based on serology (human and bovine) and two isolations of C-CHFV from non-human sources (1,2). This report represents the first documented case of acute human C-CHFV infection in Kenya. The hospital concerned belongs to a VHF surveillance network serving to increase awareness and preparedness within Kenyan health-care facilities. In this case suspicion of VHF was raised, and the patient was immediately isolated, noninvasive procedures were instigated, and barrier nursing was implemented to prevent nosocomial transmission. No family or hospital staff member who had close contact with the patient became ill. Although VHFs are rare, this report stresses the need for health facilities in Kenya and East/Central Africa to include VHFs in their differential diagnosis of unexplained fever with hemorrhagic tendencies, as well as the utility of the surveillance network. The causative agents of Ebola hemorrhagic fever, Marburg hemorrhagic fever, C-CHFV, Rift Valley fever, and yellow fever are all endemic in East and Central Africa, and sporadic cases, as well as outbreaks, are likely to continue to occur in this region (3–5).

The Use of a Mobile Laboratory Unit in Support of Patient Management and Epidemiological Surveillance during the 2005 Marburg Outbreak in Angola

Background Marburg virus (MARV), a zoonotic pathogen causing severe hemorrhagic fever in man, has emerged in Angola resulting in the largest outbreak of Marburg hemorrhagic fever (MHF) with the highest case fatality rate to date. Methodology/Principal Findings A mobile laboratory unit (MLU) was deployed as part of the World Health Organization outbreak response. Utilizing quantitative real-time PCR assays, this laboratory provided specific MARV diagnostics in Uige, the epicentre of the outbreak. The MLU operated over a period of 88 days and tested 620 specimens from 388 individuals. Specimens included mainly oral swabs and EDTA blood. Following establishing on site, the MLU operation allowed a diagnostic response in <4 hours from sample receiving. Most cases were found among females in the child-bearing age and in children less than five years of age. The outbreak had a high number of paediatric cases and breastfeeding may have been a factor in MARV transmission as indicated by the epidemiology and MARV positive breast milk specimens. Oral swabs were a useful alternative specimen source to whole blood/serum allowing testing of patients in circumstances of resistance to invasive procedures but limited diagnostic testing to molecular approaches. There was a high concordance in test results between the MLU and the reference laboratory in Luanda operated by the US Centers for Disease Control and Prevention. Conclusions/Significance The MLU was an important outbreak response asset providing support in patient management and epidemiological surveillance. Field laboratory capacity should be expanded and made an essential part of any future outbreak investigation.

Investigation of tick-borne viruses as pathogens of humans in South Africa and evidence of Dugbe virus infection in a patient with prolonged thrombocytopenia.

In the course of investigating suspected cases of viral haemorrhagic fever in South Africa patients were encountered who had been bitten by ticks, but who lacked evidence of infection with Crimean-Congo haemorrhagic fever (CCHF) virus or non-viral tick-borne agents. Cattle sera were tested by enzyme-linked immunoassay to determine whether tick-borne viruses other than CCHF occur in the country. The prevalence of antibody in cattle sera was 905/2116 (42.8%) for CCHF virus, 70/1358 (5.2%) for Dugbe, 21/1358 (1.5%) for louping ill, 6/450 (1.3%) for West Nile, 7/1358 (0.5%) for Nairobi sheep disease, 3/625 (0.5%) for Kadam and 2/450 (0.4%) for Chenuda. No reactions were recorded with Hazara, Bahig, Bhanja, Thogoto and Dhori viruses. The CCHF findings confirmed previous observations that the virus is widely prevalent within the distribution range of ticks of the genus Hyalomma, while antibody activity to Dugbe antigen was detected only within the distribution range of the tick Amblyomma hebraeum. Cross-reactivity for the nairoviruses, Hazara, Nairobi sheep disease and Dugbe, was detected in serum samples from 3/72 human patients with confirmed CCHF infection, and serum from 1/162 other patients reacted monospecifically with Dugbe antigen. The latter patient suffered from febrile illness with prolonged thrombocytopenia.

Yellow Fever Outbreak, Southern Sudan, 2003

In May 2003, an outbreak of fatal hemorrhagic fever, caused by yellow fever virus, occurred in southern Sudan. Phylogenetic analysis showed that the virus belonged to the East African genotype, which supports the contention that yellow fever is endemic in East Africa with the potential to cause large outbreaks in humans.