Serologic evidence of respiratory and rickettsial infections among Somali refugees.

Somali refugees living in a camp located in Djibouti were studied in October 1991 and May 1992. The refugees had been living at the camp for about two years. The median age of volunteers was 25 years, of whom 69% were female. Paired sera obtained seven months apart were evaluated by complement fixation, microimmunofluorescence, indirect fluorescent antibody, streptococcal antibody, and enzyme-linked immunosorbent assay techniques for evidence of pathogen infection. Fifty-two percent, 31.3%, 8.0%, 5.9%, and 25.4% of the volunteers had serologic evidence for pre-enrollment infection with Chlamydia pneumoniae, Mycoplasma pneumoniae, Rickettsia typhi, R. conorii, and Coxiella burnetti, respectively. Similarly, 43.5%, 5.2%, 6.1%, 10.7%, 15.8%, and 11.9% of the volunteers studied had serologic evidence for new infection with Streptococcus pyogenes, C. pneumoniae, M. pneumoniae, R. typhi, R. conorii, and Cox. burnetii, respectively. These data suggest that the studied pathogens may be endemic in displaced populations living in the Horn of Africa.

Sand fly fever-Naples infection in Egypt.

Two Egyptian male patients with sand fly fever-Naples virus infection are presented. The virus was isolated from one patient while both patients had diagnostic rises in indirect fluorescent antibody titers to the virus. The viral isolate, SFN 85055, grows to much higher titers and plaques more efficiently than the prototype sand fly fever-Naples virus and should facilitate work with this virus.

Application of an immunoperoxidase monolayer assay for the detection of arboviral antibodies.

An immunoperoxidase monolayer assay (IPMA) was adapted for the detection of antibodies to six arboviruses: three viruses within the flavivirus group (dengue 2, West Nile (WN) and yellow fever) and three in the phlebovirus group (Rift Valley fever (RVF), sandfly fever Naples and sandfly fever Sicilian). Antibody titers of homologous hyper-immune mouse ascitic fluid (HMAF) measured by IPMA were two to eight-fold less than those determined by ELISA. In tests with heterologous HMAF, cross-reactions frequently observed in ELISA, particularly in the flavivirus group, were absent in all IPMA titrations. With human serum samples tested for antibodies to RVF (n = 52) and WN (n = 90), the sensitivity of IPMA as compared with ELISA was 96 and 91%, respectively, specificity of IPMA was 100%. In addition, the IPMA format has several advantages that make it a useful alternative to ELISA for diagnosing arboviral infections under field conditions.

Epidemic dengue 2 in the city of Djibouti 1991-1992.

From October 1991 to February 1992, an outbreak of acute fever (in which thick blood films were negative for malaria) spread rapidly in the city of Djibouti, Djibouti Republic, affecting all age groups and both nationals and foreigners. The estimated number of cases was 12,000. The clinical features were consistent with a non-haemorrhagic dengue-like illness. Serum samples from 91 patients were analysed serologically for flavivirus infection (dengue 1-4, West Nile, yellow fever, Zika, Banzi, and Uganda-S), and virus isolation was attempted. Twelve strains of dengue 2 virus were isolated. Dengue infection was confirmed by a 4-fold or greater rise in immunoglobulin (Ig) G antibody in paired serum specimens, the presence of IgM antibody, or isolation of the virus. Overall, 46 of the suspected cases (51%) were confirmed virologically or had serological evidence of a recent flavivirus infection. Statistical analysis showed that the presence of a rash was the best predictor of flavivirus seropositivity. In November 1992, Aedes aegypti was widespread and abundant in several districts of Djibouti city. A serological study of serum samples collected from Djiboutian military personnel 5 months before the epidemic showed that only 15/177 (8.5%) had flavivirus antibodies. These findings, together with a negative serosurvey for dengue serotypes 1-4 and yellow fever virus performed in 1987, support the conclusion that dengue 2 virus has only recently been introduced to Djibouti.

Remote village survey for agents causing hepatosplenic disease in the Republic of Yemen.

The objective of this study was to epidemiologically describe potential infectious agents among rural people in the Republic of Yemen. This would aid clinicians in designing empirical therapy and public health officials in planning disease prevention. We sought to examine evidence for the geographical distribution of pathogens causing human hepatic and splenic disease among villagers and domestic animals living in three remote areas with differing altitudes. In June 1992, a cross-sectional survey was conducted at three survey sites of differing altitudes: 3080, 1440 and 250 m above sea level. Questionnaires, parasitic and serological tests were administered to 627 human volunteers. Additionally 317 domestic animals were studied. Malaria, schistosomiasis, and hepatitis B and C infections were found to be likely causes of human hepatic or splenic disease. Additionally, evidence of human and animal infections with the agents of brucellosis and Q fever was found: IgG antibodies against hepatitis E virus were discovered in two (2.0%) of the 100 volunteers. The prevalence of markers for human and animal disease was often lowest at the village of highest elevation, suggesting that increasing altitude, as a surrogate or a true independent risk factor, was protective against infection with the agents studied.

Solid-phase immunosorbent technique for rapid detection of Rift Valley fever virus immunoglobulin M by hemagglutination inhibition.

A solid-phase immunosorbent technique (SPIT) was adapted to detect Rift Valley fever (RVF) virus-specific immunoglobulin M (IgM) in serum samples from humans vaccinated with Formalin-inactivated RVF vaccine. Microdilution plates coated with goat anti-human IgM were successively incubated with serum samples from human vaccinees, RVF virus hemagglutinating antigen, and goose erythrocytes. The RVF virus-specific IgM in the serum samples from vaccinees bound to the RVF virus antigen and inhibited hemagglutination of goose erythrocytes. SPIT was compared to the IgM capture enzyme linked immunosorbent assay (ELISA) and the indirect immunofluorescent-antibody (IFA) assay and was found to be sensitive in detecting RVF virus-specific IgM antibody, with high correlations between SPIT and the other two tests (Pearson's correlation coefficient [r] = 0.9 and 0.6, respectively). Results of SPIT were obtained within 5 h, offering speed over ELISA (8 h). In addition, SPIT does not require sophisticated equipment or expensive reagents. Serum rheumatoid factor did not produce false-positive reactions in SPIT as in the indirect immunofluorescent-antibody assay and IgM capture ELISA.

Evaluation of a competitive enzyme immunoassay for detection of Coxiella burnetii antibody in animal sera.

A competitive enzyme immunoassay (CEIA) was established and compared with other serological techniques for detecting Coxiella burnetii antibody in camels, goats, and sheep. This technique was evaluated because a conjugated anti-camel immunoglobulin was not available to serve as a direct signal for the demonstration of antigen-antibody reaction. A C. burnetii antibody-positive human serum and a peroxidase-conjugated anti-human immunoglobulin G were used as an indicator system competing against antibody in animal serum or as an indicator of the absence of antibody. Sera were considered antibody positive when the A414 of the test sera plus the competing positive antibody was less than or equal to 50% of the A414 of the negative-control serum plus the competing antibody. Antibody to C. burnetii was repeatedly demonstrated in 66% of camel serum samples (n = 200) by the CEIA. Among 48 camel serum samples, 71% were positive for antibody by CEIA versus 65% by EIA using peroxidase-labeled protein A. The CEIA detected C. burnetii antibody in 63% of sheep serum samples (n = 40) and in 50% of goat serum samples (n = 96), while the indirect fluorescent-antibody technique detected antibody in 38% of sheep and 34% of goat serum samples and the EIA detected antibody in 50% of sheep and 35% of goat serum samples. These data indicate that the CEIA is a reliable and sensitive technique for demonstrating C. burnetii antibody in camels, sheep, and goats.

Serological evidence of Crimean-Congo haemorrhagic fever viral infection among camels imported into Egypt.

A serosurvey was conducted during 1986-87 to determine evidence of prior Crimean-Congo haemorrhagic fever (CCHF) viral infection among camels imported into Egypt from Sudan and Kenya. Sera obtained from camesl arriving at the Aswan quarantine station, southern Egypt, were tested for CCHF antibody by the agar gel diffusion (AGD) and the indirect fluorescent antibody (IFA) techniques. CCHF viral antibody was demonstrated in 14% (600/4301) of the camels, with both techniques yielding similar results. CCHF viral antibody prevalence among camels imported from Sudan was lower (12%) than among camels imported from Kenya (26%). Ganjam and Qalyub viral antibody was not detected among the 600 CCHF viral antibody positive sera, but 7% (44/600) were positive for Dugbe viral antibody. CCHF viral antibody was not demonstrated in 400 sheep and 200 cows of native animals. These data indicate that camels imported from Sudan and Kenya had previous CCHF viral infection, but evidence of transmission to animals of Egypt was not obtained. Further studies are needed to assess the possible role of imported animals in the ecology and epidemiology of CCHF virus in Egypt.

Antigenic variation of wild and vaccine rabies strains of Egypt.

Nineteen street rabies virus strains, isolated in Egypt from humans (two), dogs (nine), cats (two), farm animals (two), gerbils (three), and a jackal were antigenically analyzed. The Pasteur strain used for the preparation of human rabies vaccine, the Flury high and low egg passage stains (HEP, LEP) used for animal vaccines, and the challenge virus standard (CVS) strain were also assayed. All were examined by the indirect fluorescent antibody test, using a panel of 20 monoclonal antibodies against the nucleocapsid of rabies and rabies-related viruses. The rabies isolates demonstrated patterns of reactivity with the antinucleocapsid panel different from those of the Pasteur, HEP, and CVS strains. Representative human, dog, and rodent isolates were analyzed by neutralization tests in mice, with a second panel of 19 monoclonal antibodies against rabies and Mokola envelope glycoproteins. With this panel, the isolates demonstrated patterns of reactivity different from the vaccine strains. These data indicate antigenic variation between wild virus and vaccine strains.

Seroprevalence of Rickettsia typhi and Rickettsia conorii infection among rodents and dogs in Egypt.

A serological survey of 1813 rodent and 549 dog sera, collected from 1979 to 1986 from animals in 16 Egyptian Governorates were tested for antibody to Rickettsia typhi and Rickettsia conorii by the indirect fluorescent antibody test. Only three of 82 (4%) sera from Rattus rattus collected near Aswan had antibody to R. conorii. The prevalence of R. typhi antibody in dog sera was only 0.4% (n = 549) while 25% (n = 547) of Rattus norvegicus and 11% (n = 1138) of R. rattus had measurable antibodies. Among the other rodents, antibody was demonstrated in only 2% (n = 45) of Arvicanthis spp., and 1% (n = 83) of Acomys spp. Collectively, rodents captured in the Nile Delta had a higher prevalence (mean 24% (n = 787] than those captured in the Nile Valley (mean 4% (n = 650]. Antibody to R. typhi was detected in rodents collected in all port cities: ismailiya, 13%; Port Said, 9%; Suez, 9%; Safaga, 16%; Quseir, 32% and Alexandria, 34%. These data showed evidence of R. typhi infection among rodents in widespread geographic localities of Egypt and suggested that infected rodents may be a source of human infections.

Seroprevalence of murine typhus and fièvre boutonneuse in certain human populations in Egypt.

A study was conducted between 1984 and 1987 to determine the prevalence of Rickettsia typhi and Rickettsia conorii infections among humans residing in the Nile Delta, Suez Canal area and Nile Valley of Egypt. Serum specimens were obtained from garbage and rodent control workers, other unclassified occupational workers, and from patients with fever of undetermined aetiology. All sera were assayed for IgA + IgM + IgG (IgAMG) antibody mixture and if positive, reassayed for specific IgM antibody to rickettsia by the indirect fluorescent antibody technique. R. typhi antibody was found in 19% (33/178) of the garbage collectors, whereas only 1% (2/178) had demonstrable antibody to R. conorii. Among those with other occupations, R. typhi antibody was detected in 0.7% (2/295) and none had R. conorii antibody. The antibody prevalence rate for R. typhi among patients with febrile illness ranged from 25 to 41%, and from 2 to 15% for R. conorii, at three different locations in Egypt. In addition, IgM antibody to R. typhi was demonstrated in some patients showing symptoms compatible with rickettsial disease and in some patients who seroconverted, indicating that R. typhi was the cause of illness among some of these patients. These findings support previous observations that R. typhi and R. conorii are the causes of human rickettsial disease in Egypt, and that humans are commonly infected with R. typhi.

Coxiella burnetii antibody prevalences among human populations in north-east Africa determined by enzyme immunoassay.

Retrospective serosurveys were conducted to determine the prevalence of antibody to phase-I Coxiella burnetii among humans in various locations of north-east Africa. Sera were tested by the enzyme immunoassay (EIA). Initially the EIA was compared with the standard indirect fluorescent antibody (IFA) method for the detection of antibody to C. burnetii. Results indicated that the EIA was slightly less sensitive (88%), but highly specific (94%) and less subjective than the IFA technique. EIA was subsequently adopted for estimating prevalences in the studied human populations. Data obtained by EIA indicated that the prevalence of C. burnetii antibody among adult Egyptian blood donors was 20% (n = 358) in the Suez Canal area, 16% (n = 501) in the Nile Valley and 10% (n = 427) in the Nile Delta. Among adult patients with acute, undifferentiated fever in Egypt, the prevalence was 28% (n = 50) of acute sera, with seroconversion in 12% of convalescent sera. Antibody to C. burnetii was detected by EIA in the sera of 25% (n = 71) of cattle workers in Egypt, 10% (n = 100) of housewives in Sudan, and 37% (n = 104) of adults in north-west Somalia. Following a fever outbreak affecting all ages in northern Sudan, IgG antibody to C. burnetii was present in 54% of the febrile persons (n = 185) and in 53% of afebrile persons (n = 186). IgM antibody to C. burnetii was demonstrated in 29% of the febrile persons and 15% of the afebrile persons. These results implicate C. burnetii as a possibly important and under-reported cause of human disease and undiagnosed fevers in north-east Africa.

Rift Valley fever in Egypt 1986. Surveillance of sheep flocks grazing in the northeast Nile Delta.

From October 1985 through November 1986, 1714 presumably unvaccinated sheep in 13 nomadic flocks located in four provinces in Dakahliya Governorate, in the northeast Nile Delta, were ear tagged and monitored for acquisition of Rift Valley fever virus (RVFV) antibodies. Sheep were bled at approximately 3 month intervals and sera were tested for haemagglutination inhibition (HI) antibodies to RVFV. HI reactors were tested for RVFV specific IgM antibody by enzyme-linked immunosorbent assay (ELISA) and neutralizing antibody to RVFV by plaque reduction neutralization (PRN) tests. Base line results showed 1.2% prevalence of HI antibody to RVFV with titres from 1:20 to 1:320. All HI positive sera were PRN positive through PRN titres were generally higher than HI titres. No RVFV specific IgM antibody was detected in the HI and PRN positive sera. Throughout the study, no initially seronegative sheep became positive and no HI positive sheep showed an appreciable increase above initial antibody titre. These data indicate absence of RVFV transmission to sheep in Dakahliya Governorate during the period of the study.

Serological evidence of dengue fever among refugees, Hargeysa, Somalia.

Epidemics of a malaria-like illness affected several thousand residents of the Dam Camp, a refugee camp near Hargeysa in Somalia, during 1985, 1986, and 1987. The disease was characterized by fever, chills, sweats, headache, back and joint pains for as long as 10 days in some patients. Blood smears from acutely ill patients were negative for malaria. Of 28 acute and 10 convalescent sera tested by the indirect fluorescent antibody (IFA) and by the hemagglutination inhibition (HI) tests, all were negative for antibody to Rift Valley fever, Crimean-Congo hemorrhagic fever, Sindbis, Chikungunya, yellow fever, and Zika viruses. However, antibody reactive to dengue 2 virus was detected by the IFA test in 39% (15/38), and 11 of 29 (38%) of the same sera were antibody positive by the HI test. Also, IgG antibody reactive to dengue 2 was demonstrated in 60% (17/28) of the same sera by the enzyme immunoassay (EIA), and 14% (4/28) were positive for IgM antibody. Of ten patients for which acute and convalescent sera were available, two developed four fold or greater rises in antibody titer evidencing infection. These data suggested that dengue virus may have been the cause of the epidemic among the Dam Camp refugees.