RESULTS

Table 1 showed that Staphylococcus spp. was the most frequently isolated organism from the cases of ulcerative lymphangitis examined with a frequency of 30.56%. Corynebacterium spp. was next with 22.22% and the least frequently isolated was Streptococcus spp. having a frequency of isolation of 11.11%. The remaining samples yielded no growths (36.11%).

Table 2 showed that A. fumigatus was the most frequently isolated fungus with a frequency of 38.46%, followed by A. niger with a frequency of 26.9%, then Mucor spp. (23.08%) and lastly Trichophyton spp. having a frequency of 11.54%.

Table 1:	Frequency of isolation of bacterial organisms associated with ulcerative lymphangitis in Kano, Nigeria

Table 2:	Frequency of isolation of fungal organisms associated with ulcerative lymphangitis in Kano, Nigeria

Table 3:	Antibiotics sensitivity of Corynebacterium spp. associated with ulcerative lymphangitis in Kano, Nigeria

Table 4:	Antibiotics sensitivity of Staphylococcus spp. associated with ulcerative lymphangitis in Kano, Nigeria

Table 5:	Antibiotics sensitivity of Streptococcus spp. associated with ulcerative lymphangitis in Kano, Nigeria

Table 3 showed the inhibitory effects of commonly used antibiotics on Corynebacterium spp. Ciprofloxacin had complete inhibitory effect indicating highest sensitivity. This was followed by pefloxacin, gentamicin, septrin and erythromycin. The least sensitivity was exhibited by zinnacef, amoxicillin, rocephin and streptomycin.

Table 4 showed the inhibitory effects of commonly used antibiotics on Staphylococcus spp. It showed that gentamicin, amoxycillin and ciprofloxacin had a high inhibitory effect, while pefloxacin, zinnacef, streptomycin and septrin had a lower inhibitory effect. Staphylococcus spp. showed resistance to rocephin and erythromycin.

From Table 5, it could be seen that amoxycillin had a complete inhibitory effect on Streptococcus spp. Ciprofloxacin and erythromycin also had high inhibitory effects. Pefloxacin, gentamycin and zinnacef exhibited low sensitivity. Streptococcus spp. was resistant to rocephin and septrin.

DISCUSSION

Breed predisposition has not been a topic of discussion with regards susceptibility to ulcerative lymphangitis. But in this research, the most frequently affected horses belonged to either of the ‘Arewa’, ‘Sudan’ or ‘Talon’ breeds (all Arabian cross in nature). This may be due to management practices. The expensive and Argentine horses used for polo are usually managed under strict hygienic conditions because they are highly valuable, thus they are less likely to pick up this infection as it is related to poor hygiene. It was also observed from this study that the most affected horses were between the ages of 3 and 7 years. Conceivably, this could be attributed to a high level of activity seen at this age range which normally results in injuries that could get contaminated with the micro-organisms that cause ulcerative lymphangitis. This finding agreed with the report by Pratt (2009) which states that ‘horses of 1- 5 years of age are more susceptible to infection by Corynebacterium pseudotuberculosis, but adult horses of any age could be affected’. It was also observed from this research, relying on available records, that ulcerative lymphangitis was more prevalent during the rainy season. This is in agreement with reports by Khan et al. (2005) who stated that Corynebacterium pseudotuberculosis infection in horses is seasonal, with a peak incidence in late summer and fall. This can be attributed to the favorable environment for bacterial proliferation available during the rainy season due to high moisture and humidity. Some of the cases of ulcerative lymphangitis from which samples were collected had lesions on the pectoral muscles (Fig. 1) which showed that they had “pigeon breast” form of the disease. Some other ones showed typical nodular and ulcerative lesions affecting the entire limbs (Fig. 2) which agreed with descriptions given by Khan et al. (2005). The disease caused by Corynebacterium pseudotuberculosis is said to manifest in three different forms which are: ulcerative lymphangitis, external and internal abscesses (Aleman and Spier, 2002).

The pattern of organisms isolated from the cases of ulcerative lymphangitis from Kano metropolis is in agreement with the findings of Azizuddin and Chandrasekharam (1954) and Bain (1963), who in their various studies, reported possible aetiologies of lymphangitis to include Corynebacterium pseudotuberculosis, Staphylococcus spp. and Streptococcus spp., etc. Table 1 showed the presence of other bacteria such as Staphylococcus and Streptococcus aside the main causative agent, Corynebacterium pseudotuberculosis. This is because ulcerative lymphangitis is commonly associated with a wound which serves as a likely portal of entry for other bacteria.

Fig. 1:	Lesion on the breast muscle of a horse in Kano, Nigeria caused by Corynebacterium pseudotuberculosis infection showing typical ‘Pigeon breast’ form of the disease

Fig. 2:	Lesions of ulcerative lymphangitis in a horse in Kano, Nigeria, showing typical pattern of attack on the lymphatic vessels which may affect the entire limb

Fig. 3:	Microscopic appearance of Corynebacterium pseudotuberculosis isolated from a horse with ulcerative lymphangitis in Kano, Nigeria showing typical gram positive rods at X 1000 magnification

The specific species of Corynebacterium isolated in this study is Corynebacterium pseudotuberculosis. This is because the bacteria isolated were gram positive rods with typical Chinese letter arrangements (Fig. 3). They exhibited a narrow zone of β-hemolysis when cultured on sheep blood agar, they were catalase positive, fermenters on oxidative fermentative medium, urease positive and nitrate negative being distinguishing features for Corynebacterium pseudotuberculosis as reported by Efstratiou and George (1999). Though fungal agents have been incriminated in the disease process of ulcerative lymphangitis aside bacteria, no specific species have been implicated to the best of our knowledge. In this study however, fungal agents such as Aspergillus fumigatus, A. niger, Trycophyton spp. and Mucor spp. were isolated (Table 2). The cases could not have been said to be epizootic lymphangitis because the dimorphic fungus, Histoplasma capsulatum var farciminosum was not isolated which is reported as the causative agent of epizootic lymphangitis (OIE, 2008). The findings in this work with regards the fungal isolates, may explain why ulcerative lymphangitis has been refractory to treatment with antibiotics in Kano.

The antimicrobial susceptibility tests carried out on the three bacterial isolates in this study generally revealed that the fluoroquinolones (especially ciprofloxacin) and the penicillins (especially amoxicillin) consistently exhibited high efficacy against all the bacteria. This was so probably because of the fact that the fluoroquinolones, being a third generation group of antibiotics, are bactericidal and have a broad spectrum of activity; therefore they are very potent and resistance to them by bacteria is minimal. The penicillins on the other hand were also very effective probably because they have high specificity for gram-positive bacteria. Next in efficacy were the aminoglycosides (especially streptomycin and gentamycin) and then the macrolide antibiotics especially erythromycin. The other antibiotics were zinnacef, rocephin and septrin which exhibited very low sensitivity and even complete resistance in some instances.

CONCLUSION AND RECOMMENDATIONS

From the results of this research, it can be said that Corynebacterium pseudotuberculosis, Staphylococcus spp., Streptococcus spp. and fungi are involved in the disease process of ulcerative lymphangitis. Ciprofloxacin and amoxicillin are the most effective antibiotics against the bacterial agents responsible for ulcerative lymphangitis in Kano, Nigeria.

It is therefore recommended that in the management of horses, a high level of hygiene should be observed. All skin wounds and bruises should be promptly washed, disinfected and dressed to prevent contamination with bacteria and fungi which could progress to ulcerative lymphangitis.

In the treatment of cases of ulcerative lymphangitis, a drug sensitivity test should be carried out on organisms encountered. Where this is not possible, the fluoroquinolones or penicillins can be used with a degree of certainty to produce favorable results. The first choice is ciprofloxacin because it is bactericidal, broad spectrum, distributes well in tissues and more importantly for our case, it is known to accumulate in the macrophages and polymorphonuclear leucocytes thus effective against intracellular organisms (Aliu, 2007; Dowling et al., 2008) and the main causative agent here is Corynebacterium pseudotuberculosis which is said to be intracellular. The use of antifungal agents both topically and systemically is also recommended.

Finally, it is worth mentioning that this disease has threatened the entire equine population in Nigeria and the developing world alike raising a fundamental issue about equine welfare (Fazili and Kirmani, 2011).