A study on Newcastle disease outbreaks in Zambia,

Transcription

1 Rev. sci. lech. Off. int. Epiz., 1985, 5 (1), A study on Newcastle disease outbreaks in Zambia, R.N. SHARMA*, N.A. HUSSEIN***, O.S. PANDEY** and M.N. SHANDOMO* Summary: The incidence of Newcastle disease in the Republic of Zambia between 1975 and 1984 is reviewed. A total of 525 outbreaks were confirmed during this period. The disease is widespread in the country and the number of outbreaks/unit time in an area is directly related to the size of the total population of poultry. There are two peaks of outbreaks annually one in the hot dry season of September to November and another during the hot humid season of January to March. The majority of outbreaks are in village chickens. Education of traditional farmers on poultry husbandry and encouragement to vaccinate their flocks are essential in the control of Newcastle disease in Zambia. KEYWORDS: Disease control - Epidemiology - Husbandry methods - Laboratory diagnosis -Newcastle disease virus - Poultry - Poultry diseases - Vaccination - Zambia. INTRODUCTION Newcastle disease was first reported in Zambia in native fowls at Mazabuka, in the Southern Province, in May, In later years it was found occurring in poultry populations throughout the country (Anon., ). Commercial farms experienced minimum losses compared to village poultry in which the disease was responsible for heavy mortality. Slaughter of contacts and vaccination of poultry at risk has been the policy of the Government for effective control. In spite of these measures, sporadic outbreaks of the disease still occur. Hence, a study was made to review the incidence of the disease between 1975 and 1984 in order to correlate the control measures and factors related to the maintenance of the disease. The findings are reported in this communication. MATERIALS AND METHODS Laboratory diagnosis Specimens from suspected cases of Newcastle disease (ND), according to clinical history and post-mortem findings, were collected in 50% buffered glycerine for virus isolation. * School of Veterinary Medicine, University of Zambia, P.O. Box 32379, Lusaka, Zambia. ** Central Veterinary Research Institute, P.O. Box 33980, Lusaka, Zambia. *** Arab League Technical Assistance.

2 6 Laboratory diagnosis of ND was based on the isolation of virus in embryonated chicken eggs and its identification by the haemagglutination inhibition test (HI) with specific ND sera. All diagnostic procedures were performed at the poultry pathology laboratory of the Central Veterinary Research Institute (CVR1), Republic of Zambia. RESULTS The details of the confirmed outbreaks are presented in Tables I and II and Figures 1 and 2. TABLE I Provincial distribution of ND in Zambia, Provinces/Year Total Lusaka* Southern Central Copperbelt Northern Northwestern Western Eastern Luapula 1 r * Lusaka Province was created in TABLE II Monthly distribution of ND in Zambia, Year/months Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Total

3 7 FIG. 1 Newcastle disease outbreaks: comparison with poultry production and vaccine usage

4 8 FIG. 2 The Republic of Zambia. Distribution of Newcastle disease outbreaks ( )

5 9 Provincial distribution of ND The provincial distribution of ND throughout the country is depicted in Figure 2 and is related to the density of poultry populations. The highest incidence occurred equally in Central and Southern Province followed by Lusaka and Copperbelt Provinces. Annual incidence of ND During the last decade ( ) a total of 525 outbreaks was confirmed in the laboratory. The highest incidence was recorded in 1975, after which there was a decreasing trend. However, an erratic variation in positive cases for each year was noticed. In 1980, only two outbreaks were confirmed. This could be due to the moving of the diagnostic laboratory from Mazabuka to Lusaka, which resulted in an interruption in availability of diagnostic facilities. A few specimens might not have been processed for virus isolation during that year. Seasonal distribution of ND From the results of the monthly incidence shown in Table II, two peaks of outbreaks are observed. One peak is during September to November, the hot dry season of the year. Another peak, although lower, is during January to March, the hot moist season of the year. Incidence of ND before 1975 For the purpose of review, the incidence of ND outbreaks before 1975 is presented in Table III. The information was obtained from the records of the disease diagnostic section of the CVRI and the Annual Reports of the Department of Veterinary and Tsetse Control Services ( ). Except for 1953, outbreaks occurred in every year. However, no information is available for the years 1969 and DISCUSSION It is a statutory requirement that all suspect cases of Newcastle disease be reported to the Office of the Department of Veterinary and Tsetse Control Services. Upon laboratory confirmation, legislation stipulates that a "Newcastle infected area" be declared. The infected area normally covers a radius of about 20 kilometres around the outbreak area. Regulations remain in effect for two months following the last confirmed outbreak. Movement of all avian species in and out of the infected area is forbidden. In the meantime, contact birds are slaughtered and the surrounding population at risk is vaccinated. Following independence, urban expansion has proceeded at a rapid rate. This expansion has been mostly along "the main railway lines", from Southern Province, running through Lusaka and Central Provinces to Copperbelt region. In order to meet the demand for poultry products in this urbanised population, the poultry industry developed rapidly in these provinces. As a result, the size of many small backyard flocks was increased without any improvement in management standards. These flocks are maintained under poor hygienic conditions. At the same time, a number of large commercial and well-managed poultry units, holding up to 100,000 or more birds, was established.

6 10 TABLE III Newcastle disease outbreaks ( ) Year Number of Location Vaccine usage Year outbreaks (Province) Vaccine usage Southern 64,500* 1953 Nil - 57, Central 60, Eastern 73, Eastern 79, Southern Central 137,982 Copperbelt Copperbelt 86, Copperbelt 2, Northeastern 2. 74, Western 1, Central , Southern 13, Central 7, Northwestern 3, 216,616 Luapula Central 3, Northwestern 3, Southern 2, 253,020 Southern 2, Northern 1, Western Central 4, Northeastern 2, 57,235 Luapula Western 8, Central 1. 87, Distribution not given 93, Central 7, Western and Northwestern 3. 35, Central 15, Southern 8, Western , Central 14, Western 4, Southern , Central 9, Copperbelt 3, Southern 12, Eastern ,000

7 11 TABLE III (contd.) Newcastle disease outbreaks ( ) Year Number of outbreaks Location (Province) Vaccine usage Central 21, Copperbelt 21, Southern 11, Luapula 1, Northwestern Central 28, Copperbelt 31, Southern 7, Eastern 7, Northern 1, Western , ,246 * Egg-adapted live vaccine (Komarov), obtained from the Onderstepoort Laboratory, RSA, was used during In Zambia, the disease was first diagnosed in 1952 in Southern Province and, in a very short time (1957), it was known to have spread to the major poultry producing areas of the country. A high number of outbreaks was always recorded in areas on "the main railway lines". Exception to this statement is noted in Northern and Eastern Provinces. Table I shows that regular outbreaks were not experienced in Northern and Eastern Provinces. However, devastating outbreaks were recorded in Northern Province during 1979 and in Eastern Province during 1975 and contributed to the large cumulative total. Examination of records (Table III) prior to 1975 also shows a similar distribution of ND outbreaks. The highest number was always recorded in Central Province followed by Southern and Copperbelt Provinces. Lusaka Province was created in 1976 out of some areas from Central and Southern Provinces. Most of the poultry production farms around the capital city of Lusaka, which were previously in the Central Province, fell within the newly created Lusaka Province. The exact population distribution of poultry in each province is not available. However, taking a conservative figure, three-quarters of the total poultry of the country is reared in areas on the main railway lines. Hence, it is obvious that the number of outbreaks/unit time in an area is directly related to the size of the poultry population. Most of the outbreaks recorded during the observation period ( ) were in the traditional sector. Since the fifties it has been accepted that ND is enzootic in native reserves (Anon., 1957). The difference in disease incidence between traditionally and commercially managed flocks can be explained by the differences in vaccination and husbandry practices followed under these two management systems. A survey conducted by the diagnostic section of CVR1 during on the vaccination cover of poultry in Copperbelt and Lusaka Provinces showed that only ten percent of the traditional farmers vaccinate. Although this survey was

8 12 conducted in only two provinces, it is likely that a similar pratice is followed in other provinces. Irregular and inadequate supply of vaccine means that even commercial farmers are sometimes unable to vaccinate certain batches of chicks. Hence, a variable immune status in different batches of birds on the same farm is not uncommon. This could explain the occasional outbreaks in the commercial sector. The vaccination programme includes application of live lentogenic vaccine, preferably B Hitchner or F strains, at 1 day of age by intranasal or intraocular route. This vaccination is usually done by hatchery before chicks are sold to customers. Revaccination is at 28 to 35 days of age, using lentogenic vaccines in drinking water. Broilers get these two vaccinations. Layers are revaccinated at 10 weeks of age preferably by La Sota vaccine in drinking water. When available, a few farmers preferred Komarov vaccine at 10 weeks. Layers get revaccination at point of lay and thereafter usually at six month intervals during their laying period. The choice of vaccine for these vaccinations is B1 Hitchner or La Sota strains, depending on their availability. Free vaccination coverage for Newcastle disease has been the policy of the Government. However, due to financial constraints and other unforeseen reasons, this policy could not continue smoothly after 1978, when pharmaceutical companies and hatcheries were encouraged to import vaccines to supplement the Government efforts. A good correlation between vaccine usage and the outbreaks has been noticed. Use of low dosage of vaccine during 1974 in relation to the growing poultry population resulted in a sharp rise of outbreaks in the following year. However, a large application of vaccine by the Department alone during (Figure 1) contributed to a marked decrease in the incidence of the disease in subsequent years. Vaccine application by the Government agency was low during and the amount of vaccine provided by the private companies is not available for correlation. However, the vaccination survey results ( ) showed that vaccine import by private sources fulfilled the demand of vaccine at least for progressive poultry men. Because of isolation and poor communication with village communities, vaccination has not become popular in rural areas and foci of infection remained amongst village flocks. Outbreaks of ND have a seasonal occurrence (Table II). The findings coincide well with the climatic conditions in Zambia. September to November is a hot dry season with increased wind-flow throughout the country. Airborne spread of ND is well-known (1, 5, 6, 8). During the clinical phase of the disease, the virus is discharged from the respiratory tract (7) and with viscerotropic strains, the virus is also excreted in the faeces. Virus in the faecal material can remain viable for 21 days and during this period of the year faeces can soon become dry and airborne as dust particles (2). In Zambia the involvement of viscerotropic velogenic strains in ND outbreaks have been recognised (4). Another peak of outbreaks is observed when the climate is hot and humid and occasionally in heavy rains, with cool, humid weather. A cool moist climate also favours the airborne transmission of the virus (2). ACKNOWLEDGEMENTS The authors wish to thank Dr H.G.B. Chizyuka, Assistant Director of Research, Central Veterinary Research Institute, for providing facilities, Mr A. Hakantu for technical assistance and Mrs Millie Njovu for secretarial assistance. * * *

9 13 ÉTUDE SUR LES FOYERS DE MALADIE DE NEWCASTLE EN ZAMBIE DE 1975 A R.N. Sharma, N.A. Hussein, G.S. Pandey et M.N. Shandomo. Résumé : Les auteurs passent en revue l'incidence de la maladie de Newcastle en Zambie de 1975 à Au total, 525 foyers ont été confirmés pendant cette période. La maladie est largement répandue dans le pays et le nombre de foyers par unité de temps dans une zone est en relation directe avec l'importance de la population aviaire. L'épizootie présente deux pics annuels, le premier pendant la saison chaude et sèche de septembre à novembre, et le second pendant la saison chaude et humide de janvier à mars. La plupart des foyers se produisent dans les petites exploitations villageoises. Apprendre aux fermiers traditionnels à appliquer de bonnes méthodes d'élevage avicole et les encourager à vacciner leurs volailles sont des facteurs essentiels pour la prophylaxie de la maladie de Newcastle en Zambie. MOTS-CLÉS : Diagnostic expérimental - Epidemiologic - Maladies des volailles - Méthodes d'élevage - Prophylaxie - Vaccination - Volailles - Virus de la maladie de Newcastle - Zambie. * * * ESTUDIO DE LOS FOCOS DE ENFERMEDAD DE NEWCASTLE EN ZAMBIA DE 1975 A R.N. Sharma, N.A. Hussein, G.S. Pandey y M.N. Shandomo. Resumen : Los autores pasan revista a la incidencia de la enfermedad de Newcastle en Zambia de 1975 a Durante este periodo se confirmaron en total 525 focos. La enfermedad está muy extendida por el país y el número de focos por unidad de tiempo en un área está en relación directa con la importancia del censo aviar. Presenta la epizootia dos picos anuales, el primero durante la estación cálida y seca de Septiembre a Noviembre, y el segundo durante la estación cálida y húmeda de Enero a Marzo. Se produce la mayoría de los focos en la pequeñas granjas de los pueblos. La enseñanza a los granjeros tradicionales para que apliquen correctos métodos de cría avícola y los incentivos para que vacunen a las aves son factores básicos para el control de la enfermedad de Newcastle en Zambia. PALABRAS CLAVE : Aves - Control - Diagnóstico experimental - Enfermedades de las aves - Epidemiología - Métodos de cría - Vacunación - Virus de la enfermedad de Newcastle - Zambia. * * REFERENCES 1. ALLAN W.H. (1972). Newcastle disease control. Agriculture, 79 (10), ALLAN W.H., LANCASTER J.E. & TOTH B. (1978). Newcastle disease vaccines. Their production and use. FAO Animal Production and Health Series No. 10, Rome. 3. ANON. Annual reports, Department of Veterinary and Tsetse Control Services, Republic of Zambia,

10 14 4. HUSSEIN N.A., SHARMA R.N., ANDO R. & CHIZYUKA H.G.B. (1984). A study on Newcastle disease virus pathotypes in Zambia. Rev. sci. tech. Off. int. Epiz., 3 (2), LANCASTER J.E. (1966). Newcastle disease: A review ( ). Ottawa, Can. Dep. Agric. Monogr LANCASTER J.E. (1975). Newcastle disease: Virus and spread. Ottawa, Can. Dep. Agric. Monogr SINHA S.K., HANSON R.P. & BRANDLY C.A. (1954). Aerosol transmission of Newcastle disease in chickens. Amer. J. Vet. Res., 15, SMITH C.V. (1964). Some evidence for the windborne spread of fowl pest. Met. Mag., 93,