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Medical and veterinary entomology1997; 11(3); 203-212; doi: 10.1111/j.1365-2915.1997.tb00397.x

The spatial and seasonal distribution of African horse sickness and its potential Culicoides vectors in Morocco.

Abstract: African horse sickness (AHS) is a vector-borne, infectious disease of equines that is caused by African horse sickness virus (AHSV). The only proven field vector is the biting midge Culicoides imicola, although C. obsoletus and C. pulicaris are suspected vectors. There was a recent epizootic of AHS in Iberia (1987-90) and Morocco (1989-91). In 1994-45 a total of 3887 light trap samples were taken from twenty-two sites distributed over most of Morocco. Culicoides imicola was found to be very widely dispersed, with the greatest catches in the low-lying northwestern areas (between Tangier and Rabat) and at Marrakech. Culicoides imicola was absent at one site only, near Settat. Culicoides imicola was found at altitudes ranging from 4 to 1275 m and in climatic conditions ranging from subhumid to saharan. In general, the catch of C.imicola peaked in late summer and autumn, with a smaller peak in spring. In areas where the insect appears most abundant at least one adult C.imicola per night may be caught in a light trap at all times of year, thus providing a possible means of viral overwintering. Culicoides obsoletus and C.pulicaris are also widely distributed in Morocco but trap catches were much lower than for C.imicola. Peak catches occurred in spring, and late summer and autumn. Other frequently caught species were C.circumscriptus, C.newsteadi, C.puncticollis and members of the odibilis subgenus. In general, the findings for C.imicola correspond well with the distribution of disease outbreaks during the epizootic. Although disease outbreaks were widespread in the country, the greatest number of reported cases was in the northwest (1989-90); in 1991 there were also significant numbers in Marrakech province. No cases were reported in a large area to the west of the Atlas mountains (including Settat) despite the presence of a large equine population. It is likely that during the epizootic the virus overwintered in the northwest (1989) and in Marrakech province (1990). Disease outbreaks occurred from July to December, with a peak from September to November. An unexplained phenomenon is the large number of reported cases of AHS in mules in Chefchaouen province in 1990, despite the apparent low abundance of C.imicola at a site at Chefchaouen. It is argued that C.obsoletus and C.pulicaris were probably of little significance to the epidemiology of AHS in Morocco in 1989-91.
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Publication Date: 1997-07-01 PubMed ID: 9330250DOI: 10.1111/j.1365-2915.1997.tb00397.xGoogle Scholar: Lookup
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  • Comparative Study
  • Journal Article
  • Research Support
  • Non-U.S. Gov't

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research discusses the distribution of African Horse Sickness and its possible vectors in Morocco. The investigation reveals that a midge known as Culicoides imicola, which has been found to be the only proven vector, is very widely disbursed, especially in the low-lying northwestern areas and Marrakech.

Introduction

  • The research paper focuses on the distribution of African Horse Sickness (AHS), an infectious disease affecting horses and caused by a virus. The disease is transmitted by Culicoides imicola, a specific species of biting midge.
  • The study also includes the potential role of other Culicoides species such as C. obsoletus and C. pulicaris which are suspected vectors.

Methods and Sampling

  • In 1994-95, 3887 light trap samples were taken from twenty-two sites distributed over most parts of Morocco to study the distribution of these vectors.
  • The presence and dispersal of the midge Culicoides imicola were studied across different altitudes and climatic conditions.

Findings

  • Culicoides imicola was found to be widespread, occurring in areas from 4 to 1275 meters of altitude and in climates ranging from subhumid to Saharan.
  • The greatest catches of Culicoides imicola were in the low-lying northwestern areas (between Tangier and Rabat) and in Marrakech.
  • This midge shows two population peaks during the year, one in spring and the most significant one in late summer and autumn, offering a potential channel for the virus to survive during winter.
  • Other variants such as Culicoides obsoletus and C. pulicaris were also found in Morocco, but their population was much lower compared to C. imicola. Their population also peaked in spring, and again in late summer and autumn.

Distribution and Outbreaks

  • The location and timing of AHS outbreaks matched quite well with the distribution of Culicoides imicola. Most cases of AHS were reported in the northwest and in Marrakech province.
  • An unexplained anomaly was the high number of reported AHS cases in mules in Chefchaouen province in 1990, even though Culicoides imicola was less abundant there.

Conclusion

  • The research suggests that the species Culicoides obsoletus and C. pulicaris probably did not significantly contribute to the spread of African Horse Sickness in Morocco during 1989-91, primarily because their populations were much lower than that of Culicoides imicola.

Cite This Article

APA
Baylis M, el Hasnaoui H, Bouayoune H, Touti J, Mellor PS. (1997). The spatial and seasonal distribution of African horse sickness and its potential Culicoides vectors in Morocco. Med Vet Entomol, 11(3), 203-212. https://doi.org/10.1111/j.1365-2915.1997.tb00397.x

Publication

Medical and veterinary entomology
ISSN: 0269-283X
NlmUniqueID: 8708682
Country: England
Language: English
Volume: 11
Issue: 3
Pages: 203-212

Researcher Affiliations

Baylis, M
  • Institute for Animal Health, Pirbright, U.K.
el Hasnaoui, H
    Bouayoune, H
      Touti, J
        Mellor, P S

          MeSH Terms

          • African Horse Sickness / epidemiology
          • African Horse Sickness / transmission
          • Animals
          • Ceratopogonidae
          • Geography
          • Horses
          • Insect Vectors
          • Morocco / epidemiology
          • Population Density
          • Seasons

          Citations

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