Serological and virological characterization of clinically diagnosed cases of measles in suburban Khartoum

Inoculation of raccoons with a wild-type-based recombinant canine distemper virus results in viremia, lymphopenia, fever, and widespread histological lesions

Raccoons are naturally susceptible to canine distemper virus (CDV) infection and can be a potential source of spill-over events. CDV is a highly contagious morbillivirus that infects multiple species of carnivores and omnivores, resulting in severe and often fatal disease. Here, we used a recombinant CDV (rCDV) based on a full-genome sequence detected in a naturally infected raccoon to perform pathogenesis studies in raccoons. Five raccoons were inoculated intratracheally with a recombinant virus engineered to express a fluorescent reporter protein, and extensive virological, serological, histological, and immunohistochemical assessments were performed at different time points post inoculation. rCDV-infected white blood cells were detected as early as 4 days post inoculation (dpi). Raccoon necropsies at 6 and 8 dpi revealed replication in the lymphoid tissues, preceding spread into peripheral tissues observed during necropsies at 21 dpi. Whereas lymphocytes, and to a lesser extent myeloid cells, were the main target cells of CDV at early time points, CDV additionally targeted epithelia at 21 dpi. At this later time point, CDV-infected cells were observed throughout the host. We observed lymphopenia and lymphocyte depletion from lymphoid tissues after CDV infection, in the absence of detectable CDV neutralizing antibodies and an impaired ability to clear CDV, indicating that the animals were severely immunosuppressed. The use of a wild-type-based recombinant virus in a natural host species infection study allowed systematic and sensitive assessment of antigen detection by immunohistochemistry, enabling further comparative pathology studies of CDV infection in different species. IMPORTANCE Expansion of the human interface supports increased interactions between humans and peridomestic species like raccoons. Raccoons are highly susceptible to canine distemper virus (CDV) and are considered an important target species. Spill-over events are increasingly likely, potentially resulting in fatal CDV infections in domestic and free ranging carnivores. CDV also poses a threat for (non-human) primates, as massive outbreaks in macaque colonies were reported. CDV pathogenesis was studied by experimental inoculation of several species, but pathogenesis in raccoons was not properly studied. Recently, we generated a recombinant virus based on a full-genome sequence detected in a naturally infected raccoon. Here, we studied CDV pathogenesis in its natural host species and show that distemper completely overwhelms the immune system and spreads to virtually all tissues, including the central nervous system. Despite this, raccoons survived up to 21 d post inoculation with long-term shedding, supporting an important role of raccoons as host species for CDV.

Co-detection of the measles vaccine and wild-type virus by real-time PCR: public health laboratory protocol

In rare cases vaccination with the measles virus vaccine genotype A (MeVA) may cause a vaccine reaction with clinical signs similar to infection with wild-type measles virus (MeVwt). Rapid differentiation between MeVA and MeVwt infection is important for taking adequate public health measures. Recently, a few MeVA real-time reverse-transcription quantitative PCR methods (RT-qPCRs) were described that can distinguish between MeVA and MeVwt. However, detection of MeVA does in theory not exclude infection with MeVwt. In the present study, we established a protocol for determination of co-infections with MeVA and MeVwt. To this end, MeVA RT-qPCRs were used in combination with the routine measles virus (MeV) RT-qPCR, and the results suggested that the differences between the RT-qPCR Ct values (delta Ct, ∆Ct) could be used as criteria. Subsequently, we tested samples from vaccine-associated measles cases that were confirmed by genotyping. In addition, experimental mixtures of MeVA and MeVwt were tested in different concentrations. All tested MeVA clinical samples had ∆Ct ≤3.6. The results of experimental mixtures showed a mean ∆Ct ≤2.8 for genotype A alone and >3.2 when combined with either genotype B3 or D8. The results of a receiver operator characteristic analysis indicated that the optimum ∆Ct for use as a cut-off value was 3.5, while with ∆Ct values of 2.9 and 3.7 sensitivity and specificity were respectively 1.00. Thus, ∆Ct could be used to exclude the presence of MeVwt if MeVA is detected and ∆Ct is <2.9, while ∆Ct >3.7 were highly suggestive of co-infection and ≥2.9 ∆Ct <3.7 warranted additional confirmation, such as next-generation sequencing. This RT-qPCR-based protocol could be used for the exclusion of infection with MeVwt in cases with vaccine-associated measles reaction, crucial for the timely implementation of public health prevention and control measures.

A measles outbreak in Kansai International Airport, Japan, 2016: Analysis of the quantitative difference and infectivity of measles virus between patients who are immunologically naive versus those with secondary vaccine failure

Since the elimination of the measles virus, patients with vaccination records for the measles-containing vaccine have increased in Japan. According to several studies, the transmission risk from previously immunized patients, especially those with secondary vaccine failure (SVF), is lower than that from those with primary measles infections. Immunological features of SVF were identified per specific immunoglobulin G (IgG) induction with high avidity and high plaque reduction neutralization antibody concentration. However, the virological features of SVF have not been well investigated. To examine not only immunological but also virological differences between SVF and immunologically naive patients, throat swabs and blood and urine specimens of 25 patients with confirmed measles infection after an outbreak at the Kansai International Airport in 2016 were analyzed. Patients were categorized as naive (n = 3) or with SVF (n = 22) based on measles-specific IgG antibody concentrations and their avidity. Virus isolation and quantitative real-time polymerase chain reaction were performed to quantify the viral load in clinical specimens and estimate the infectivity in each specimen. The number of viral genome copies in the blood specimens of those with SVF was significantly different and approximately 1 out of 100 of that in immunologically naive patients. However, genome copy numbers in throat swabs and urine specimens were not significantly different between the groups. The virus was isolated only from those in the naive group. Our study indicated low transmission risk of the virus in patients with SVF.

Animal morbilliviruses and their cross-species transmission potential

Like measles virus (MV), whose primary hosts are humans, non-human animal morbilliviruses use SLAM (signaling lymphocytic activation molecule) and PVRL4 (nectin-4) expressed on immune and epithelial cells, respectively, as receptors. PVRL4's amino acid sequence is highly conserved across species, while that of SLAM varies significantly. However, non-host animal SLAMs often function as receptors for different morbilliviruses. Uniquely, human SLAM is somewhat specific for MV, but canine distemper virus, which shows the widest host range among morbilliviruses, readily gains the ability to use human SLAM. The host range for morbilliviruses is also modulated by their ability to counteract the host's innate immunity, but the risk of cross-species transmission of non-human animal morbilliviruses to humans could occur if MV is successfully eradicated.

Antagonism of the phosphatase PP1 by the measles virus V protein is required for innate immune escape of MDA5

The cytosolic sensor MDA5 is crucial for antiviral innate immune defense against various RNA viruses including measles virus; as such, many viruses have evolved strategies to antagonize the antiviral activity of MDA5. Here, we show that measles virus escapes MDA5 detection by targeting the phosphatases PP1α and PP1γ, which regulate MDA5 activity by removing an inhibitory phosphorylation mark. The V proteins of measles virus and the related paramyxovirus Nipah virus interact with PP1α/γ, preventing PP1-mediated dephosphorylation of MDA5 and thereby its activation. The PP1 interaction with the measles V protein is mediated by a conserved PP1-binding motif in the C-terminal region of the V protein. A recombinant measles virus expressing a mutant V protein deficient in PP1 binding is unable to antagonize MDA5 and is growth impaired due to its inability to suppress interferon induction. This identifies PP1 antagonism as a mechanism employed by paramyxoviruses for evading innate immune recognition.

Infection of lymphoid tissues in the macaque upper respiratory tract contributes to the emergence of transmissible measles virus

Measles virus (MV), a member of the family Paramyxoviridae, remains a major cause of morbidity and mortality in the developing world. MV is spread by aerosols but the mechanism(s) responsible for the high transmissibility of MV are largely unknown. We previously infected macaques with enhanced green fluorescent protein-expressing recombinant MV and euthanized them at a range of time points. In this study a comprehensive pathological analysis has been performed of tissues from the respiratory tract around the peak of virus replication. Isolation of virus from nose and throat swab samples showed that high levels of both cell-associated and cell-free virus were present in the upper respiratory tract. Analysis of tissue sections from lung and primary bronchus revealed localized infection of epithelial cells, concomitant infiltration of MV-infected immune cells into the epithelium and localized shedding of cells or cell debris into the lumen. While high numbers of MV-infected cells were present in the tongue, these were largely encapsulated by intact keratinocyte cell layers that likely limit virus transmission. In contrast, the integrity of tonsillar and adenoidal epithelia was disrupted with high numbers of MV-infected epithelial cells and infiltrating immune cells present throughout epithelial cell layers. Disruption was associated with large numbers of MV-infected cells or cell debris ‘spilling’ from epithelia into the respiratory tract. The coughing and sneezing response induced by disruption of the ciliated epithelium, leading to the expulsion of MV-infected cells, cell debris and cell-free virus, contributes to the highly infectious nature of MV.

The use of oral fluid samples spotted on filter paper for the detection of measles virus using nested rt-PCR

Measles is the leading cause of death in infants, although a vaccine is available for its prevention. At this stage of measles elimination and eradication, it is so important to confirm clinically diagnosed measles cases in the laboratory but, developing countries have troubles in collecting and maintaining the cold chain of the specimens while transporting them to the laboratories. Therefore, filter papers are good candidates for simplification of specimen collection and transportation. In this research, the effects of the temperature, at which the dried specimens were kept, and the time duration the dried specimens were kept before being tested, were studied. Since there were not enough patients' oral fluid samples available, a nested reverse transcriptase PCR (RT-PCR) that detected measles virus (MV) from dried filter papers was set up using MV infected cells diluted in sterile phosphate-buffered saline (PBS). Dried specimens were stored at -25°C, 4°C, and room temperature for 1 day, 1, 2, and 3 weeks before being tested. This method was then applied to filter paper oral fluids collected from nine clinically diagnosed measles patients in Iran in 2010 which were tested after being kept at room temperature for 1 day, 1 and 3 weeks after preparation. The results showed that dried oral fluids on filter papers are reliable specimens for the detection of MV RNA using nested RT-PCR, but the nested RT-PCR results of low titer viruses dried onto filter papers are not reproducible and reliable.

Early target cells of measles virus after aerosol infection of non-human primates

Measles virus (MV) is highly infectious, and has long been thought to enter the host by infecting epithelial cells of the respiratory tract. However, epithelial cells do not express signaling lymphocyte activation molecule (CD150), which is the high-affinity cellular receptor for wild-type MV strains. We have generated a new recombinant MV strain expressing enhanced green fluorescent protein (EGFP), based on a wild-type genotype B3 virus isolate from Khartoum, Sudan (KS). Cynomolgus macaques were infected with a high dose of rMV^KSEGFP by aerosol inhalation to ensure that the virus could reach the full range of potential target cells throughout the entire respiratory tract. Animals were euthanized 2, 3, 4 or 5 days post-infection (d.p.i., n = 3 per time point) and infected (EGFP⁺) cells were identified at all four time points, albeit at low levels 2 and 3 d.p.i. At these earliest time points, MV-infected cells were exclusively detected in the lungs by fluorescence microscopy, histopathology and/or virus isolation from broncho-alveolar lavage cells. On 2 d.p.i., EGFP⁺ cells were phenotypically typed as large mononuclear cells present in the alveolar lumen or lining the alveolar epithelium. One to two days later, larger clusters of MV-infected cells were detected in bronchus-associated lymphoid tissue (BALT) and in the tracheo-bronchial lymph nodes. From 4 d.p.i. onward, MV-infected cells were detected in peripheral blood and various lymphoid tissues. In spite of the possibility for the aerosolized virus to infect cells and lymphoid tissues of the upper respiratory tract, MV-infected cells were not detected in either the tonsils or the adenoids until after onset of viremia. These data strongly suggest that in our model MV entered the host at the alveolar level by infecting macrophages or dendritic cells, which traffic the virus to BALT or regional lymph nodes, resulting in local amplification and subsequent systemic dissemination by viremia.

Measles remains an important vaccine-preventable cause of morbidity and mortality in developing countries. The causative agent, measles virus (MV), is one of the most contagious viruses known. Measles has an incubation time of approximately two weeks, and surprisingly little is known about the early events after MV infection. Epithelial cells in the upper respiratory tract have long been considered as early target cells, but more recently alveolar macrophages (AM) and dendritic cells (DC) have been proposed as alternatives. We have infected cynomolgus macaques with a high dose of a recombinant EGFP-expressing MV strain via aerosol inhalation, to ensure that the virus had access to the entire respiratory tract. At 2 days post-infection, MV-infected mononuclear cells were detectable in the alveolar lumen but not in the upper respiratory tract. These infected cells migrated through the bronchus-associated lymphoid tissue to the draining tracheo-bronchial lymph node at 3 days post-infection. Systemic infection was initiated from this point, as observed in macaques euthanized 4 or 5 days post-infection. Thus, even though the aerosolized virus had access to epithelial cells and lymphoid tissues along the entire respiratory tract, AM and DC in the lungs were the first cells that sustained MV replication.

Depletion of measles virus glycoprotein-specific antibodies from human sera reveals genotype-specific neutralizing antibodies

Measles virus (MV)-neutralizing antibodies in sera from vaccinated subjects are mainly directed against the haemagglutinin (H) protein. It has been shown previously that depletion of vaccination-induced H-specific antibodies by co-culture of sera with cells expressing the MV Edmonston strain H glycoprotein resulted in almost complete elimination of neutralizing activity. In the present study, MV H and/or fusion (F) protein-specific antibodies were depleted from sera of naturally immune subjects. Early convalescent samples were collected 1.5 years after a well-characterized measles outbreak in Luxembourg caused by a genotype C2 virus, whilst late convalescent samples were collected from healthy Dutch subjects born between 1960 and 1970. Depletion of both H- and F-specific antibodies completely eliminated virus-neutralizing (VN) activity against MV Edmonston. However, in the early convalescent samples, residual VN antibody against wild-type MV genotype C2 was detected. This demonstrated that, although the majority of MV-specific VN antibodies recognized epitopes conserved between different genotypes, genotype-specific VN epitopes were also induced. In sera depleted of H-specific antibodies only, VN activity against MV Edmonston was not completely eliminated, demonstrating the presence of F-specific VN antibodies. In conclusion, this study demonstrated that a fraction of VN antibodies induced by wild-type MV genotype C2 does not neutralize MV strain Edmonston. In addition, it was shown that, in sera from naturally immune donors, the majority of VN antibodies are specific for MV H protein, but up to 10 % of neutralizing antibodies are specific for MV F protein.

Infection of cynomolgus macaques (Macaca fascicularis) and rhesus macaques (Macaca mulatta) with different wild-type measles viruses

Both rhesus and cynomolgus macaques have been used as animal models for measles vaccination and immunopathogenesis studies. A number of studies have suggested that experimental measles virus (MV) infection induces more-characteristic clinical features in rhesus than in cynomolgus monkeys. In the present study, both macaque species were infected with two different wild-type MV strains and clinical, virological and immunological parameters were compared. The viruses used were a genotype C2 virus isolated in The Netherlands in 1991 (MV-Bil) and a genotype B3 virus isolated from a severe measles case in Sudan in 1997 (MV-Sudan). Following infection, all rhesus monkeys developed a skin rash and conjunctivitis, which were less obvious in cynomolgus monkeys. Fever was either mild or absent in both species. Virus reisolation profiles from peripheral blood mononuclear cells and broncho-alveolar lavage cells and the kinetics of MV-specific IgM and IgG responses were largely identical in the two animal species. However, in animals infected with MV-Sudan, viraemia appeared earlier and lasted longer than in animals infected with MV-Bil. This was also reflected by the earlier appearance of MV-specific serum IgM antibodies after infection with MV-Sudan. Collectively, these data show that cynomolgus and rhesus macaques are equally susceptible to wild-type MV infection, although infection in the skin seems to follow a different course in rhesus macaques. MV-Sudan proved more pathogenic for non-human primates than MV-Bil, which may render it more suitable for use in future pathogenesis studies.

Investigation of measles and rubella outbreaks in Tamil Nadu, India—2003

The aims of the present study were to confirm measles outbreaks by detection of measles-specific IgM antibodies, isolation of measles virus, and genetic characterization to document the circulating genotypes in Tamil Nadu. Eight outbreaks were reported from six districts of Tamil Nadu, India during the period Jan-Dec 2003. Blood samples were collected for serology, urine, and throat swabs for virus isolation. Genotypic characterization of measles isolates was based on the sequence of the N gene. All the clinically suspected outbreaks (n = 8) were confirmed by serology; six out of the eight as measles and two as combination of measles and rubella highlighting the need to carry out rubella serology on measles-negative samples. Genetic characterization of three isolates obtained revealed one as genotype D4 and two as D8. Measles genotypes D4 and D8 were found to circulate in three districts of Tamil Nadu. It is necessary to be aware of the circulating genotypes within the geographical area. The information would be valuable to evaluate control measures and identify viral transmission and importation.

Evaluation of diagnostic markers for measles virus infection in the context of an outbreak in Spain

A measles outbreak occurred from January to July 2003 in Spain, despite the fact that the Plan of Eradication of Measles and its surveillance program had been set up in 2001. Different diagnostic markers for measles virus infection were compared for 246 patients in tests of serum, urine, and pharyngeal exudate specimens. Measles virus immunoglobulin M (IgM) and IgG and rubella virus and parvovirus IgM levels in serum were assayed. Multiplex PCR was done on urine, serum, and pharyngeal exudates, and isolation of measles virus in the B 95 a cell line from urine was attempted. At least one positive marker for measles virus was obtained from 165 patients (67.1%; total number of patients, 246). A total of 136 cases (82.4% of the patients showing positive markers) were diagnosed by PCR and/or isolation and IgM detection methods. The results for 27 patients (16.4%) were positive only by direct methods. The results for two patients (1.2%) were positive only by IgM detection. In the case of the first group (136 cases), the time elapsed from appearance of the rash was significantly longer than in the case of the group which was only positive by PCR. Besides, 8 out of 27 PCR-positive IgM-negative cases showed specific IgG results, suggesting either secondary vaccine failure or reinfection. Numbers resulting from PCR performed with pharyngeal exudates proved to be significantly higher than those obtained with other specimens. Phylogenetic analysis showed the presence of genotype B3. The results strongly back the World Health Organization recommendation that detection of IgM should be supplemented by PCR and isolation for the diagnosis of measles virus infection.

Development of a semi-quantitative real-time RT-PCR for the detection of measles virus

Real-time detection of polymerase chain reactions allows convenient detection and quantification of virus-derived nucleic acids in clinical specimens. We have developed a real-time RT-PCR assay for the detection of measles virus (MV) genomic RNA, and compared it to a well-established conventional RT-PCR assay. Based on a serial dilution of the live-attenuated MV Edmonston Zagreb vaccine, the detection limits were approximately 0.1 and 0.02 cell culture infectious dose 50% units (CCID50) per test for the conventional and TaqMan RT-PCR assays, respectively. Furthermore, tissue materials spiked with known quantities of MV were equally well detected in both assays. The TaqMan assay was linear within a range of 10(4.4) to 10(-0.6)CCID50/ml, with an intra-assay variability lower than 3% and an inter-assay variability ranging from 1.5% at 10(4.4)CCID50/ml to 8.7% at 10(-0.6)CCID50/ml. The TaqMan assay could detect representative wild-type viruses from the currently active MV clades, and could detect MV genome in clinical specimens obtained from measles patients. Finally, quantification of MV RNA in peripheral blood mononuclear cells or broncho-alveolar lavage cells from cynomolgus macaques collected at different time points after experimental infection showed a good correlation with virus isolation data. In conclusion, the TaqMan assay developed is specific, sensitive, rapid and reproducible, and can be of use for diagnostic purposes or for studies on the pathogenesis of measles.

Laboratory investigations are indispensable to monitor the progress of measles elimination--results of the German Measles Sentinel 1999-2003

BACKGROUND

The elimination of measles is a goal set by the World Health Organisation to be reached by 2010 in the European region.

OBJECTIVES

To enhance the measles surveillance in Germany, a country-wide laboratory supported a sentinel was established.

STUDY DESIGN

A network of >1200 representatively distributed practitioners reported detailed data on all clinically diagnosed cases and provided specimens for laboratory diagnosis.

RESULTS

A total of 3225 suspected cases were reported between October 1999 and December 2003. The incidence in Western Germany decreased from >15 cases per 100,000 population to one case in 2003, while in Eastern Germany <1 case per 100,000 population was observed during these years. Laboratory investigations were undertaken in 40% of cases in 2000/2001. This rate increased to 79% in 2003. Simultaneously, the rate of confirmed cases dropped from 60% in the former years to 23% in 2003. Measles virus (MV) detection by serology and by PCR revealed concordant results in 92%. Most suspected cases (85%) were unvaccinated with 66% being laboratory confirmed. Only 10% of suspected cases occurred in vaccinated individuals and very few (22%) could be confirmed. Analyses of confirmed measles in vaccinated patients (n = 49) revealed 24.5% primary vaccine failures, 24.5% reinfections after successful vaccination and 31% MV infection before or shortly after vaccination. The genetic characterisation of 389 MV isolates identified eight genotypes: B3, C2, D4, D5, D6, D7, G2 and H1. Only the C2, D6 and D7 MV genotypes circulated endemically in Western Germany. The newly emerged MV D7 almost completely replaced the pre-existing C2 and D6 MVs in 2001. The few measles cases detected in Eastern Germany were mostly caused by imported MVs.

CONCLUSION

The data demonstrate that laboratory investigations including molecular methods are an indispensable tool for surveillance in all countries advanced in measles elimination.

Surveillance of measles in the Sudan using filter paper blood samples

Dried blood spots collected on filter paper are considered potential clinical specimens for measles surveillance because of their ease of collection, storage, and transport. The usefulness of these samples for surveillance of measles was evaluated in a field setting. Blood spots were collected by finger-prick from 316 clinically diagnosed measles patients in suburban Khartoum, mostly within a week after onset of the rash. Samples were collected between October, 2000 and April, 2003, and stored at 4 degrees C. Measles virus-specific IgM antibodies were detected in 200 (63%) of the samples using an "in-house" IgM capture ELISA. For 201 samples reconstitution and IgM measurement was repeated 1 year after initial testing with essentially the same results, showing the stability of IgM in the filter paper under these conditions. In a limited number of samples (n = 38) measles virus-specific IgM was also tested with a commercial indirect IgM ELISA. Although the results of the two assays correlated well, the "in-house" IgM capture ELISA proved slightly more sensitive. Measles virus-specific reverse transcriptase polymerase chain reaction (RT-PCR) amplicons were obtained from 16 of 57 (28%) samples tested. Sequencing of the 3' 456 nucleotides of the nucleoprotein gene showed the continued endemic circulation of genotype B3 viruses identified previously in this region. Although problems related to limited sample quantities were encountered, the present study confirms the usefulness of dried blood spots for measles surveillance. The results also demonstrate that measles continues to be endemic in the Sudan.

Measles virus protein-specific IgM, IgA, and IgG subclass responses during the acute and convalescent phase of infection

The availability of new generation serological assays allowed re-evaluation of the antibody response to measles virus. IgM, IgA, total IgG, and IgG subclass responses were studied to the three major immunogenic measles virus proteins: the fusion protein (F), haemagglutinin (H), and nucleoprotein (N). Plasma samples were obtained from clinically diagnosed measles cases (n = 146) in Khartoum (Sudan) within a week after onset of the rash. Convalescent phase samples were collected from 32 of 117 laboratory-confirmed measles cases at different time points after onset of rash. Glycoprotein-specific IgM, IgG, and IgA antibody levels correlated well to the N-specific response. For IgG and IgA, responses to F were higher than to H. IgA antibody levels were undetectable in about one third of the laboratory-confirmed cases during the acute phase, but positive in all patients tested 1-4 weeks after infection. IgM levels declined rapidly and were lost 3-6 months after infection. IgA levels declined slowly during the first year but did not return to background levels during the subsequent 2 years. IgG avidity maturation was detected during a 3-6 month period after infection. The predominant IgG subclasses during the acute phase were IgG(1) and IgG(3). The latter was lost in the convalescent phase, while the IgG(4) isotype showed a slight rise afterwards. Interestingly, acute phase IgG(3) and IgA responses were associated, and were only detected in samples with high IgG. This study provides a comprehensive perspective on the antibody response to wild-type measles virus infection.

Limited diversity of measles field isolates after a national immunization day in Burkina Faso: progress from endemic to epidemic transmission?

Despite recent National Immunization Days in Burkina Faso, the rural province of Houët reported >400 measles cases in 2001 (82% not vaccinated). Phylogenetic analysis of 58 measles virus field isolates plus the first sequences from the Democratic Republic of the Congo and the Republic of Congo are reported. All viruses were genotype B3, which is common in the region. In Houët, there were two geographically confined genetic variants, suggesting two independent importation events. Strain diversity in Houët (1.5%) and the Congos was limited in comparison with Ibadan, Nigeria (4.6%), where measles is endemic. Strain variability, assessed by heteroduplex mobility assay, confirmed these findings. Despite large local pools of susceptible persons even after several rounds of vaccination, the limited strain diversity suggests that parts of rural Burkina Faso may be moving from an endemic to an epidemic transmission pattern of measles virus.

Comparative evaluation of measles virus-specific RT-PCR methods through an international collaborative study

Comparison of RT-PCR assays established in house at various places revealed that laboratories could differ in sensitivity by as much as 1,000-fold in terms of the ability to detect measles virus sequences in clinical samples. The study indicates that PCR findings, positive or negative, are questionable if they are not supported by the associated data demonstrating the overall sensitivity of the assay applied. Measles virus-specific RT-PCR-based assays need to be validated using standard virus preparation or nucleic acid-based target templates. A correlation between real-time quantitative PCR and the conventional PCR for measles virus is highly desirable.

Development of an enzyme-linked immunosorbent assay for immunoglobulin M antibodies against measles virus

Measles is a highly contagious respiratory virus infection, with typical clinical symptoms including maculopapular rash, fever, cough, coryza, and conjunctivitis. Despite implementation of widespread vaccination programs throughout the world, the rates of global morbidity and mortality are still considerable. This study was performed to design a reliable indirect enzyme-linked immunosorbent assay (ELISA) to measure measles-specific immunoglobulin M (IgM). First, human IgM was purified, and then an anti-IgM antibody was produced in rabbits and purified in a multistep process. The rabbit IgG against human IgM was conjugated with peroxidase. Measles virus-infected Vero cells produced viral antigen. One hundred serum samples from infants of 9 to 18 months of age, mostly vaccinated, were evaluated for determining the presence of specific IgM antibodies against measles virus. The samples were also evaluated for neutralizing antibodies against measles virus by a microneutralization test (MNT). By comparing the results of the ELISA with those of MNT, it was demonstrated that ELISA had a sensitivity and specificity of 100 and 92%, respectively. On the other hand, when the results obtained by our ELISA system were compared with those of an imported measles virus IgM ELISA kit (EIAgen; Adaltis Italia SPa, Bologna, Italy), a high level of agreement was shown (k = 0.926).

Detection of measles virus RNA in whole blood stored on filter paper

The purpose of this study was to evaluate the use of dried blood spots stored on filter paper as a means to provide specimens for virologic surveillance for measles virus (MV) in situations when the reverse cold chain is not available. Two single-step RT-PCR assays were evaluated for sensitivity of detection of MV nucleoprotein gene RNA. The more sensitive assay was then used to assess the stability of MV RNA in dried whole blood stored on filter paper. MV RNA was found to be stable in dried blood spots for up to 2 months at room temperature or 1 month at 37 degrees C. As few as 100 infected human peripheral blood mononuclear cells (PBMC) per blood spot could be detected using a single-step RT-PCR reaction and ethidium bromide detection. MV RNA was also detected in dried blood spots obtained from rhesus macaques after challenge with wild-type MV. In the rhesus samples, the single-step RT-PCR reaction could detect approximately 10(3) TCID(50) per blood spot, while nested PCR detected 3 TCID(50) per blood spot. The results of this laboratory-based study suggest that the use of dried blood spots stored on filter has the potential to improve virologic surveillance for MV in some areas, and they emphasize the need for continued testing under field conditions.

Detection of measles virus genomic RNA in tear samples from a patient with measles keratitis

PURPOSE

To report a case of measles keratitis, in which measles virus genomic RNA was detected in tear samples.

METHODS

Samples of tears and pharyngeal mucus were obtained from a 19-year-old man with active systemic measles on day 7 after illness onset. These specimens were then subjected to reverse-transcriptase polymerase chain reaction (RT-PCR), using measles-specific primers.

RESULTS

One week after systemic measles outbreak, the patient presented with a chief complaint of irritation in both eyes. Slit-lamp examination revealed bilateral superficial punctate keratopathy in the central cornea with small diffuse subepithelial infiltrations, and RT-PCR detected measles virus genomic RNA in tears and pharyngeal mucus. The patient was treated with topical 0.1% fluorometholone and 0.5% levofloxacin three times a day for 1 week, and the keratopathy resolved without sequelae.

CONCLUSION

This report demonstrates for the first time the presence of measles virus genomic RNA in the tears of a patient with measles keratitis. It also highlights the utility of RT-PCR for rapid detection of measles RNA in tear or mucus samples. Furthermore, the presence of virus in bodily fluids and secretions signifies the potential contagiousness of this type of keratopathy.

Genetic characterization of wild-type measles viruses circulating in suburban Khartoum, 1997-2000

Measles remains endemic in many East African countries, where it is often associated with high morbidity and mortality. We collected clinical specimens from Sudanese measles patients between July 1997 and July 2000. Sequencing of the 3' 456 nucleotides of the nucleoprotein gene from 33 measles virus (MV) isolates and 8 RNA samples extracted from clinical specimens demonstrated the presence of a single endemic MV strain with little sequence variation over time (overall nucleotide divergence of 0 to 1.3%). This was confirmed by sequencing of the complete H gene of two isolates from 1997 and two from 2000, in which the overall divergence ranged between 0 and 0.5%. Comparison with MV reference strains demonstrated that the viruses belonged to clade B, genotype B3, and were most closely related to a set of viruses recently isolated in Nigeria. Our study demonstrates a remarkable genetic stability of an endemically circulating MV strain.

Priming of measles virus-specific humoral- and cellular-immune responses in macaques by DNA vaccination

Although the currently used live attenuated measles vaccines are safe and effective, they are dependent on cold chain maintenance and are often ineffective in young infants due to interference by maternal antibody. Therefore, besides vector-based vaccines, different new generation non-replicating candidate measles vaccines are being considered, including nucleic acid vaccines. We have vaccinated cynomolgus macaques transdermally with DNA plasmids encoding measles virus (MV) proteins. Following two vaccinations, low serum antibody responses were detected. Wild-type measles virus challenge 1 year after vaccination showed reduced viraemia in some animals. However, accelerated humoral- and cellular-immune responses were observed in all vaccinated macaques, demonstrating successful priming by the DNA vaccines.

Measles in suburban Khartoum: an epidemiological and clinical study

Clinical and epidemiological data were collected from 187 clinically diagnosed measles patients in Haj Yousif area, suburban Khartoum. Laboratory tests confirmed the diagnosis in 141 (75%) of the cases, but demonstrated that in 46 (25%) patients the clinical symptoms were not caused by an acute measles virus (MV) infection. According to their vaccination card, 59% of the laboratory-confirmed measles cases had been vaccinated for measles. Compared with non-measles rash disease cases, confirmed measles cases more often had severe illness (P < 0.0001), were dehydrated (P=0.01) at presentation and less likely to recover without complications [OR 0.19 (95% CI 0.09, 0.39)]. There was no difference in death rate (P=0.20). Underweight [weight-for-age Z score (WAZ) <or= -2 SD] was an independent predictor of recovery with complications [OR 0.4 (95% CI 0.2, 0.99)]. Severe measles cases (those who developed diarrhoea, pneumonia, otitis media, encephalitis or haemorrhagic rash) had similar vaccination rates and time intervals since vaccination as uncomplicated measles cases. Although severe measles had lower WAZ-scores (P=0.004), none of the nutritional parameters studied were predictive of outcome. Mortality was higher in the severe measles group [OR 8.8 (95% CI 1.7, 85.2)]. In 11 of 141 confirmed measles cases serological evidence of a recent infection with another virus was found, most commonly varicella zoster virus and dengue virus; spotted fever and rubella were among the most frequent diagnoses in 17 of 47 cases of the non-measles cases.

Safety of modified vaccinia virus Ankara (MVA) in immune-suppressed macaques

Modified vaccinia virus Ankara (MVA)-based recombinant viruses have been shown to be potent vaccine candidates for several infectious and neoplastic diseases. Since a major application of these live, replication-deficient vectors would be their use in immunocompromised or potentially immunocompromised individuals, a preclinical safety study was carried out. Macaques were inoculated with high doses of MVA (10(9)) via various routes, after immune-suppression by total-body irradiation, anti-thymocyte globulin treatment, or measles virus (MV) infection. No clinical, haematological or pathological abnormalities related to MVA inoculation were observed during a 13-day follow-up period. The presence of MVA genomes was demonstrated by nested PCR during the course of the experiment in all macaques, but from none of these animals replication competent MVA could be reisolated. These data suggest that MVA can safely be used as a basis for recombinant human vaccines, and that it is also safe for use in immunocompromised individuals.

Prevention of measles in Sudan: a prospective study on vaccination, diagnosis and epidemiology

Despite the availability of safe and effective live attenuated vaccines, measles continues to be endemic in many developing countries. Control and elimination of measles will be especially difficult in East Africa, because of its limited infrastructure and political instability. We have studied diagnostic and epidemiological aspects of measles in suburban Khartoum, Sudan. Prospective studies were carried out in a cohort of clinically diagnosed measles cases and in a cohort of newborns, which were both followed up for 2 years. The studies intended to provide a rational basis for improvement of measles vaccination strategies, and strengthen measles research infrastructure in Khartoum.

Combination of reverse transcriptase PCR analysis and immunoglobulin M detection on filter paper blood samples allows diagnostic and epidemiological studies of measles

As measles control and elimination campaigns progress, laboratory confirmation of clinically diagnosed measles cases becomes increasingly important. However, in many tropical countries collection and storage of clinical specimens for this purpose are logistically complicated. In this study it is shown that blood samples spotted on filter paper are suitable for the laboratory diagnosis of measles using a combination of reverse transcriptase PCR (RT-PCR) analysis and immunoglobulin M (IgM) detection. First, it was shown that in vitro measles virus (MV)-infected cells diluted in human blood and spotted on filter paper can be detected by RT-PCR. Small amounts of infected cells remained detectable after 25 weeks of storage of the filter paper at room temperature, 4 weeks at 37 degrees C, or 2 weeks at 45 degrees C. Subsequently, this RT-PCR was applied to filter paper blood samples collected from 117 clinically diagnosed measles patients in Sudan in 1997 and 1998. Prior laboratory diagnosis had confirmed 90 cases as acute MV infections, while 27 proved to be nonmeasles rash disease cases. Positive RT-PCR signals were detected in filter paper blood samples of 43 of the 90 confirmed cases (48%) but in none of the 27 nonmeasles cases. In addition, MV-specific IgM levels measured in reconstituted filter paper samples correlated well with those measured in plasma samples. Measles diagnosis based on the combination of filter paper RT-PCR and IgM detection had a sensitivity and specificity of 99 and 96%, respectively. An advantage of this diagnostic approach is that sequencing of RT-PCR products allows phylogenetic analysis of the MV strain involved.