R. MuimoSamora Machel School of Veterinary Medicine
University of Zambia
P.O. Box 32379
Lusaka
Zambia
Summary
Resume
Introduction
Materials and methods
Results
Discussion
Acknowledgements
References
Seasonal fluctuations of trichostrongylid infections in 30 adult female and 30 kid Boer goats were studied on 2 commercial farms from January 1988. Observations included faecal egg counts every 14 d and larval culture and differentiation and haematological indices every month. Eggs per gram in adults and kids peaked in February (rainy season) and in March and began to fall at the start of the dry season in May. Larval differentiation from faecal cultures showed that Strongyloides papillosus, Haemonchus contortus and Oesophagostomum columbianum were the most prevalent species. Anthelmintics were used during the rainy season on 1 farm but egg counts did not differ greatly from the farm where none were used.
Les variations saisonnières de l'infection à trichostrongylidaes chez 30 femelles adultes et 30 jeunes boucs Boer furent étudiés dans 2 grandes fermes. Les observations comprennaient les comptes des oeufs par gramme de fécès (chaque 14 j), et la coproculture et la différenciation et les paramètres hématologiques (chaque mois). Le nombre d'oeufs par gramme chez les adultes est maximum en février (saison des pluies) alors que le taux le plus élevé chez les chevreaux est atteint en mars. Le taux d'infestation commence à diminuer au début de la saison sèche en mai. La différentiation des larves à partir de la coproculture montre que Strongyloides papillosus, Haemonchus contortus et Oesophagostomum columbianum sont les espèces dominantes. Un traitement anthelmintic fut effectué pendant la saison des pluies sur une des fermes mais le nombre moyen d'oeufs n'était pas sensiblement différent dans cette ferme par rapport à l'autre.
Goats (Zambian population about 350 000) can play a valuable role in increasing the productivity of the livestock sector in Zambia particularly as their small size, early maturity and low investment per head suit them to the needs of the peasant communities.
On most farms, goats kid at the beginning of the dry season (April) and at the onset of the rains (November). High kid mortality rates due to parasitic gastro-enteritis, particularly haemonchosis, have previously been recorded on commercial farms during the rainy season. Parasitic gastro-enteritis causes anaemia, diarrhoea, emaciation resulting in reduced weight gains, increased mortalities and increased production costs. This paper reports on epidemiological study of the pattern of infection on 2 commercial farms through 1 season.
Samples were obtained from goats on 2 commercial mixed farms situated about 40 km from Lusaka: Farm A (beef cattle and 3000 Boer goats) and Farm B (100 dairy cattle, 100 goats, some sheep). The annual rainfall of 800-1000 mm per annum falls in summer (Nov-Mar). Mean monthly temperature varies from 17°C (May-Jul) to 26°C (Dee-Mar). On Farm A faecal samples were collected every 14 d directly from the rectum of 20 females (2-3 yr) and 20 kids (2 mo). On Farm B samples were collected from 10 females and 10 kids.
Quantitative estimation of nematode eggs in the faeces was performed by the Modified McMaster technique (MAFF, 1986). Counts were expressed in egg number per gramme of faeces (epg). Selected faecal samples were cultured in moist vermiculite at 26°C. Five animals were subject to postmortem and their intestines and intestinal contents examined for worms. Blood samples were also collected from the jugular vein using ethylenediaminetetracetate (EDTA) as an anticoagulant. Packed cell volumes (PCV) were determined by the microhaematocrit method and haemoglobin concentration (Hb) was also estimated.
Anthelmintic drugs were administered to goats in Farm A monthly during the rainy season. A mixture of Ranide (Rafoxanide, MSD) and Systamex (Oxfendazole 9.06% M/V, Wellcome Foundation) in the ratio 7:1 was administered monthly from Jan-Jun 1988. Adult animals were given a mixture of 10-15 ml and kids 1-5 ml depending on body weight.
Faecal larvae culture and egg counts
Results of faecal culture indicated that Strongyloides papillosus, Haemonchus contortus and Oesophagostomum columbianum were the most prevalent species in the ratio of 20:24:1 on Farm A and 20:2:1 on Farm B. Trichostrongylus colubriformis, Cooperia spp. and Trichuris spp. were also observed.
Egg counts were highest in kids on both farms in March and April (Figure 1, Table 1) after the maximum rain had occurred. Egg counts of adult females were highest on both farms in February, at the height of the rainy season (Figure 1). Mean monthly epg was < 500 in May on Farm A and in June on Farm B (Table 1).
Figure 1. Faecal nematode egg output by goats on two commercial farms in Zambia.
Despite the use of anthelmintics on Farm A, the proportion of goats producing strongyle eggs was high and monthly epg did not differ markedly from Farm B where none were used. Mean monthly epg levels were much higher in kids during the rainy season than in adults.
Haematology
Mean monthly PCV and Hb values of adult goats and kids were relatively higher on Farm B while both values were lowest on the two farms during Jan-Apr (Tables 1 and 2).
Table 1. Faecal egg counts and haematological values of kids on two farms in Zambia.
|
Farm and month |
Monthly egg count |
PCV |
Haemoglobin |
|||||
|
Mean epg |
Range |
Positive (%) |
Mean (%) |
Range |
Mean (g/dl) |
Range |
||
|
Farm A |
|
|
|
|
|
|
|
|
|
|
Jan |
0 |
0 |
0 |
26.6 |
24-32 |
9.8 |
8.0-11.0 |
|
|
Feb |
663 |
0-8100 |
83.7 |
29.6 |
25-32 |
10.8 |
7.0-12.0 |
|
|
Mar |
8661 |
200-18200 |
100.0 |
27.1 |
20-34 |
10.1 |
8.5-11.6 |
|
|
Apr |
6172 |
0-37700 |
94.4 |
22.4 |
16-31 |
9.8 |
5.9-11.6 |
|
|
May |
214 |
0-1450 |
31.3 |
27.1 |
14-28 |
10.9 |
7.8-13.6 |
|
|
June |
44 |
0-550 |
22.2 |
24.0 |
18-29 |
9.1 |
7,1-12.2 |
|
|
July |
38 |
0-900 |
12.8 |
29.8 |
24-30 |
10.5 |
9.7-11.1 |
|
|
Aug |
62 |
0-450 |
34.4 |
24.9 |
23-30 |
9.0 |
7.4-10.9 |
|
|
Sept |
41 |
0-150 |
83.3 |
24.8 |
21-30 |
9.8 |
8.8-10.9 |
|
Farm B |
|
|
|
|
|
|
|
|
|
|
Jan |
1780 |
50-10550 |
100.0 |
26.7 |
24-35 |
9.1 |
8.0-12.2 |
|
|
Feb |
2202 |
0-10100 |
90.0 |
24.9 |
21-27 |
10.5 |
9.4-13.3 |
|
|
Mar |
8661 |
0-20500 |
100.0 |
19.1 |
11-26 |
7.5 |
5.0-9.8 |
|
|
Apr |
8615 |
1000-2400 |
100.0 |
22.6 |
16-26 |
5.8 |
6.4-10.6 |
|
|
May |
1820 |
100-5500 |
100.0 |
29.6 |
22-29 |
10.6 |
9.2-12.0 |
|
|
June |
716 |
0-2350 |
74.1 |
29.4 |
24-34 |
11.2 |
9.4-12.6 |
|
|
July |
50 |
0-150 |
42.8 |
30.8 |
26-35 |
10.6 |
9.5-12.8 |
|
|
Aug |
88 |
0-300 |
50.0 |
31.6 |
21-35 |
11.8 |
9.8-12.9 |
|
|
Sept |
53 |
0-250 |
55.0 |
30.8 |
26-33 |
11.2 |
9.8-11.8 |
Recovery of adult worms
Adult nematode species identified by examination of intestines and intestinal contents included Haemonchus contortus, Oesophagostomum columbianum, Strongyloides papillosus, Trichuris spp., Cooperia spp. and Trichostrongylus colubriformis. Other parasite species found included Stilesia hepatica, Cysticercus tenuicolis and Moniezia expanse.
Table 2. Faecal egg counts and haematological values of adult female goats in Zambia.
|
Farm and month |
Monthly egg count |
PCV |
Haemoglobin |
|||||
|
Mean epg |
Range |
Positive (%) |
Mean (%) |
Range |
Mean (g/dl) |
Range |
||
|
Farm A |
|
|
|
|
|
|
|
|
|
|
Jan |
365 |
50-700 |
100.0 |
24.1 |
20-28 |
8.7 |
7.7-10.9 |
|
|
Feb |
2006 |
0-12100 |
88.5 |
26.7 |
24-29 |
9.8 |
8.4-10.6 |
|
|
Mar |
1854 |
0-7800 |
82.9 |
25.9 |
20-29 |
9.1 |
7.5-10.3 |
|
|
Apr |
2010 |
0-9000 |
80.0 |
23.5 |
20-32 |
8.9 |
7.3-10.6 |
|
|
May |
29 |
0-150 |
22.0 |
26.1 |
17-25 |
10.2 |
9.2-11.3 |
|
|
June |
26 |
0-300 |
19.7 |
24.5 |
20-29 |
9.5 |
8.2-11.1 |
|
|
July |
7 |
0-50 |
14.2 |
26.1 |
19-32 |
9.1 |
4.8-11.4 |
|
|
Aug |
62 |
0-650 |
20.9 |
28.0 |
20-30 |
9.6 |
7.4-10.9 |
|
|
Sept |
41 |
0-450 |
57.1 |
23.0 |
18-28 |
9.4 |
6.1-12.7 |
|
Farm B |
|
|
|
|
|
|
|
|
|
|
Jan |
3091 |
150-10550 |
100.0 |
30.5 |
26-34 |
10.2 |
8.5-12.2 |
|
|
Feb |
4050 |
500-89000 |
100.0 |
30.1 |
25-35 |
11.3 |
9.4-13.4 |
|
|
Mar |
1991 |
250-10580 |
100.0 |
29.3 |
22-33 |
10.8 |
9.2-13.2 |
|
|
Apr |
1885 |
250-8300 |
100.0 |
26.9 |
24-30 |
10.1 |
8.6-11.5 |
|
|
May |
1885 |
250-8300 |
100.0 |
26.9 |
16-35 |
11.3 |
6.2-13.2 |
|
|
June |
280 |
0-1400 |
90.0 |
31.0 |
27-36 |
11.6 |
7.3-13.7 |
|
|
July |
67 |
0-450 |
22.0 |
32.1 |
29-37 |
11.8 |
10.0-14.2 |
|
|
Aug |
67 |
0-300 |
33.0 |
35.3 |
30-39 |
12.7 |
10.7-13.9 |
|
|
Sept |
100 |
0-450 |
66.0 |
31.6 |
25-37 |
11.7 |
9.2-13.4 |
In spite of the fact that faecal worm egg counts are influenced by several different factors (health and age of host, nematode species, previous exposure, consistency of faeces they are often used as an indication of the course of worm infestations in sheep and goats.
In the current study, there was a seasonal pattern of egg output corresponding to the rainfall pattern (Figure 1). During the rainy season climatic conditions become more favourable resulting in increased infestation rates. Levine (1963) considered 50 mm or more rainfall and 15°C to 37°C mean monthly temperature as optimum conditions for pasture transmission of Haemonchus contortus. Dinnik and Dinnik (1960) considered a minimum rainfall of 20 mm in a 10 d period was required for Haemonchus larvae to develop. Improved environmental conditions may also stimulate larvae in a state of arrested development within the host to mature, thus causing epg to increase. As pastures begin to dry in April and most of the soil is exposed to direct sunlight, the level of infective larvae on pasture falls, leading to a reduction in egg count. Infection is transmitted from adult animals to the young ones as both graze the same pasture, this accounting for the later peak in egg output by young.
The prevalence of Haemonchus contortus and Oesophagostomum columbianum in goats in Zambia has previously been reported (Lovelace et al, 1988). High levels of Strongyloides papillosus could have been due to poor housing conditions including moisture and dirt.
The rationale behind anthelmintic application during the rainy season is to reduce worm burdens and egg contamination of pasture to a minimum. Despite anthelmintic use, the high proportion of Haemonchus contortus on Farm A suggests resistance to the drugs used. A monthly application of an anthelmintic for 6 mo can be sufficient to cause resistance depending on the selection pressure it imposes (van Wyk and Malan, 1988). Further trials are in progress to confirm the extent of resistance.
Haematological examination indicated that PCV and Hb values declined during periods of high egg output although this was in wet weather when pasture was lush. Despite poor dry season pasture, PCV and Hb values returned to normal with a decline in egg output. PCV and Hb values were lower on Farm A due to a higher infestation with Haemonchus contortus. Haemonchosis, in its acute form, is associated with severe anaemia. Allonby and Urquhart (1975) observed that in chronic haemonchosis in sheep, haematological values continue to be significantly depressed, although slightly above those seen in acute haemonchosis, and the animals appear clinically normal.
The International Foundation for Science is thanked for financial assistance and R J Thomas for his help and advice. Special thanks are due to Parasitology Laboratory staff for their technical assistance.
Allonby E W and Urquhart G M. 1975. The epidemiology and pathogenic significance of haemonchosis in a Merino flock in East Africa. Veterinary Parasitology 1: 129-143.
Dinnik J A and Dinnik N N. 1958. Observations on the development of Haemonchus contortus larvae under field conditions in the Kenya highlands. Bulletin of Epizootic Diseases in Africa 6: 11-21.
MAFF 1986. Manual of veterinary parasitological techniques. Reference Book 418. Her Majesty's Stationery Office, London, UK.
Levine N D. 1963. Weather, climate and the bionomics of ruminant nematode larvae. Advances in Veterinary Science 8: 215-261.
Lovelace C E, Persson, E, Tada Y. Koomson, T O M, Amoo C C, Nakazawa M, Daka J K and Nyirenda I. 1988. Paper presented at the Second National Science Fair on Scientific and Technological Research for Development, Lusaka, Zambia.
van Wyk J A and Malan F S. 1988. Resistance of field strains of Haemonchus contortus to Ivermectin, Closantel, Rafoxanide and the benzimidazoles in South Africa. Veterinary Record 123: 226-228.
