Host feeding of mosquitoes (Diptera: Culicidae) associated with the recurrence of Rift Valley fever in Egypt.

In 1993, Rift Valley fever (RVF) virus reappeared in Egypt. We determined the prevalence and feeding patterns of mosquitoes in 5 villages where the virus was active. Of 10 species recovered, Aedes caspius (Pallas), Culex pipiens L., Cx. antennatus (Becker), and Cx. perexiguus Theobald constituted 99% of > 35,000 mosquitoes captured in dry ice-baited CDC light traps. Ae. caspius was most prevalent, except at Nag' El Hagar where it was replaced by Cx. perexiguus. Cx. pipiens ranked 2nd, except at Nag' El Ghuneimiya, where it was replaced by Cx. antennatus. Most blood meals analyzed by an enzyme-linked immunosorbent assay reacted to > or = 1 antiserum. Cx. pipiens was mainly anthropophagic, and therefore may have been the main vector of RVF virus among humans. Ae. caspius feeds were chiefly from humans, bovines, and equines. Cx. antennatus and Cx. perexiguus fed generally on bovines. Mixed blood meals from humans and RVF virus susceptible animals were identified in the predominant mosquitoes. Prevalence and host selection, as well as predicted probability for a blood meal being interrupted, indicated that Ae. caspius may have served as a bridge vector between humans and bovines in 4 of the villages. Cx. perexiguus may have played this role at Nag' El Hagar. Because potential vectors are abundant, susceptible domestic animals are associated closely with humans, and surveillance of imported livestock is not systematic, we conclude that RVF virus sporadically will recur in Egypt.

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.

Vector competence of Egyptian mosquitoes for Rift Valley fever virus.

Reintroduction of Rift Valley fever (RVF) into Egypt in 1993 raised concerns about the potential for Egyptian mosquitoes to transmit the virus. We evaluated the ability of Aedes caspius, Culex pipiens, Cx. antennatus, Cx. perexiguus, Cx. poicilipes, and Anopheles pharoensis collected in the Aswan area and Cx. pipiens collected in the Nile Delta to transmit RVF virus. All mosquito species tested were susceptible to RVF virus infection, with An. pharoensis and Ae. caspius being the most sensitive to infection. However, none of 12 An. pharoensis, including 10 with a disseminated infection, transmitted RVF virus by bite. In contrast, nearly all Cx. pipiens (87%, n = 15) and Cx. perexiguus (90%, n = 10) with a disseminated infection transmitted virus. Overall transmission rates for mosquitoes exposed to hamsters with a viremia > or = 10(7) plaque-forming units/ml were Ae. caspius, 20% (n = 5); Cx. pipiens, 7% (n = 102); Cx. antennatus, 7% (n = 30); Cx. perexiguus, 11% (n = 9); and An. pharoensis, 0% (n = 7). Based on abundance, susceptibility to infection, ability to transmit virus, and feeding behavior, Ae. caspius appeared to be the most efficient vector of the Egyptian mosquitoes evaluated. While less susceptible than Ae. caspius, Cx. pipiens, Cx. antennatus, and Cx. perexiguus were also potential vectors during this RVF outbreak in Egypt.

Assessment of arthropod vectors of infectious diseases in areas of U.S. troop deployment in the Persian Gulf.

Beginning in August 1990, approximately 800,000 coalition troops were deployed to the Persian Gulf during Operations Desert Shield and Desert Storm. There was substantial concern about arthropod-borne diseases, particularly sand fly fever and cutaneous leishmaniasis, because of high morbidity rates in the Persian Gulf during World War II (WWII). In sharp contrast to WWII, there was no report of sand fly fever among coalition forces and only 31 cases of leishmaniasis among 697,000 U.S. troops. To further evaluate the risk of arthropod-borne diseases, an entomologic survey was conducted in 12 areas of Kuwait and Saudi Arabia. A total of 1,556 arthropods was collected during four survey periods in 1992. The suspected vectors of cutaneous Leishmania major infection, sand fly fever, West Nile fever, Rift Valley fever, and Crimean-Congo hemorrhagic fever were identified; however, there was no evidence of arboviruses or Leishmania among collected specimens nor from 51 trapped rodents. There are several possible reasons for the low risk of arthropod-borne infectious diseases among Desert Shield/Storm troops in an area where suspected vectors frequently were found: the use of insecticides and repellents, and the deployment of most ground troops to the open desert during the cooler, winter period--conditions least favorable for the transmission of arthropod-borne diseases.

New record of the malaria vector Anopheles sergentii in the southern Nile Valley of Egypt.

Twelve adult female Anopheles sergentii were collected from 2 villages in the Nile River Valley in Aswan Governorate, Egypt, in August of 1993. No immature forms were found during limited sampling. This is the first record of this malaria vector in Aswan Governorate and represents the southernmost distribution in northern Africa.

Recurrence and emergence of infectious diseases in Djibouti city.

Public health authorities are now increasingly concerned by changes in the epidemiology of infectious diseases which may have an adverse impact on their budget plans and control strategies. Rapid increases in population and urban migration, various ecological changes, increasing poverty, and a rise in international travel have contributed to the worldwide vulnerability of human populations to the emergence, recurrence or spread of infectious diseases. In the rapidly growing city of Djibouti in East Africa, public health priorities have been altered during the last 10 years by diseases which were unknown or under control until the early 1980s. These diseases, including malaria, AIDS, tuberculosis, dengue fever and cholera, are consuming considerable resources. This article on Djibouti illustrates the epidemiological changes in the region. Besides the specific ecological and behavioural changes, which accompany rapid population growth, poverty seems to be a major cause for the emergence and recurrence of infectious diseases.

PIP: The growing prevalence of diseases which were unknown or under control until the early 1980s, such as malaria, AIDS, tuberculosis, dengue fever, and cholera, consume considerable resources and have changed public health priorities in Djibouti over the last 10 years. Poverty seems to be a major cause for the emergence and recurrence of these infectious diseases. Epidemiological changes in the region are discussed. Public health authorities are increasingly concerned by those changes which may have an adverse impact upon budget plans and control strategies. Rapid increases in population and urban migration, ecological changes, increasing poverty, and a rise in international travel have contributed to the worldwide vulnerability of human populations to the emergence, recurrence, or spread of infectious diseases.

Recurrence of Rift Valley fever in Egypt.

Rift Valley fever (RVF) has been recorded in man and in domestic animals in Egypt after a 12-year absence. Human infections were first noted in the Aswan Governorate in late May, 1993. Only cases of ocular disease, an infrequent and late manifestation, were reported. Of 41 cases, 35 were tested serologically and 27 (77%) had RVF virus-specific IgM antibodies. An estimated 600-1500 infections occurred in the region. Abortions in cattle and buffalo were seen concurrently and antibodies to RVFV were present in 39% of domestic livestock, presumably unvaccinated. RVFV was isolated from an aborted water buffalo fetus.

Parahost behavior of adult Gasterophilus intestinalis (Diptera: Gasterophilidae) in Delaware.

Parahost behavior of adult Gasterophilus intestinalis (DeGeer) was observed during the summers of 1978 and 1979 near pastured horses on two farms near Newark, Del. Adult fly occurrence, although sparse in early summer, indicated a gradual increase, with three surges in emergence. In the laboratory, males lived 1-3 d and females 1-2 d. In the field, marked flies were not seen on days following their release. Adult behavior indicated an urgency in mating and oviposition dictated by a short life span. Male flight patterns were characterized by in-flight searches for females and intraspecific conflicts with other males. This behavior appeared to be density dependent. Horses grazing singly or in groups were aggressively defended by hovering males. Following midair coupling, mating took place near horses. Female horse bot flies oviposited in a variety of environmental and parahost conditions. The rate of oviposition varied, but a female could deposit her total complement of 900 eggs in less than 1 h. Egg counts on hosts indicated that horses can ingest greater than 90% of the infective stage larvae through self and mutual grooming. The hanging ovipositor profile identified an ovipositionally spent female. The effective life span of an ovipositing female was 1 d.

Comparison of rDNA and mtDNA in the sibling species Anopheles freeborni and A. hermsi.

Comparison of the ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) of Anopheles freeborni and A. hermsi, 2 morphologically indistinguishable mosquito species in the North American A. maculipennis complex, revealed restriction enzyme site variation in both DNA families. Diagnostically useful interspecific differences in the rDNA were observed in the external transcribed spacer (ETS) and internal transcribed spacer (ITS) regions. The regions encoding rRNA, however, were indistinguishable with respect to the enzymes used. Intraspecific site and genome length variations were present in the mtDNA of 5 colonies of A. freeborni and 3 colonies of A. hermsi, but no species-specific differences were observed.