Etiology, epidemiology, clinical and pathological presentations of Edema disease and Edema disease-like syndromes of pigs in Kenya
Edema disease and edema disease-like syndromes are major causes of morbidity and mortality in pig herds in Kenya, yet their distinct causes are not well understood although a wide range of infectious and non-infectious agents may be involved. This study was therefore conducted to: (I) determine retrospectively and prospectively the occurrence of edema disease and edema disease-like syndromes, (2) investigate the etiology, clinical and pathological presentations of these conditions and (3) determine their morbidity and mortality rates as well as the risk factors associated with them. The study was conducted in three phases which ran concurrently. In phase I, post mortem records at the Central Veterinary Investigations Laboratories and Department of Veterinary Pathology and Microbiology for the period between January 2000 and May 2004 were used to calculate frequency of occurrence of edema disease. Phase II comprised a detailed study on all cases presented to Department of Veterinary Pathology and Microbiology for post mortem examination in the period between June 2004 and June 2007. Diagnosis of edema disease and edema disease-like syndromes was based on: clinical and pathological presentations and laboratory analyses comprising histopathology, bacterial isolation and characterization, transmission electron microscopy, recovery and identification of gastrointestinal helminths and polymerase chain reaction on all Escherichia coli isolates. In phase III, farms that submitted cases in phase II were visited twice during outbreaks. Data on morbidity, mortality, husbandry and management practices were collected. Descriptive statistics, Mann-Whitney rank sum test and analysis of variance (ANOV A) were used for data analyses. Sixty three out of 221 (28.5%) cases encountered in the retrospective study were diagnosed as edema disease. In the prospective study, 33 out of 84 cases (39.3%) examined were diagnosed as edema disease, 30 cases (35.7%) as edema disease-like syndromes while 21 cases (25%) were other conditions. Twenty four (38.1 %) of the edema disease cases were uncomplicated while 8 (12.7%) and I (1.6%) were complicated by post weaning diarrhea and chronic salt poisoning, respectively. Edema disease clinically manifested as sudden death (12), neurological disorders (13) and swollen eyelids (3) in addition to respiratory distress (9), loss of appetite (4) and recumbency (5). At post mortem, uncomplicated edema disease cases had scanty lesions (4), others (20) had variable amounts of edema, congested organs; lymphoid hyperplasia and mononuclear cellular infiltration in brain ventricles. Hemolytic E. coli isolated from gut contents harbored genes encoding for F 18 fimbrial adhesin and elaboration of shiga-like toxin type II variant (Stx2e). Edema disease complicated by post weaning diarrhea had diarrhea clinically and diphtheritic typhlocolitis at necropsy while in salt poisoning, head pressing and degeneration of cerebral neurons and mononuclear cellular infiltration into the meninges were additional clinical and pathological observations, respectively. Edema disease-like syndromes that clinically presented as sudden death (7) or neurological disorders (15) and at post mortem examination revealed presence of edema in body cavities were diagnosed as post weaning diarrhea (8), streptococcal meningitis (2), systemic salmonellosis (2), chemical poisoning (2) and inconclusive (18). Unlike edema disease complicated by post weaning diarrhea, in post weaning diarrhea, none of the hemolytic (1) and non-hemolytic (6) E. coli isolates harbored FI8 and Stx2e genes. Isolation of hemolytic Streptococcus suis from the dura matter and presence of suppurative meningitis at histopathology characterized streptococcal meningitis whereas in systemic salmonellosis, Salmonella species was isolated from the gut of pigs presenting at necropsy; yellowish diarrhea, widespread vascular necrosis and non-suppurative inflammatory lesions in the liver and kidneys. In chemical poisoning, peri-renal edema and microscopically hyalization of glomerular tufts and massive hepatic necrosis were distinctive for nephrotoxicity and hepatotoxicity, respectively. Inconclusive diagnosis was made when hemolytic (4) and non- hemolytic (18) E. coli isolated harbored none of F 18 and Stx2e genes in addition to finding no clinical signs and/or post mortem lesions characteristic of a particular disease. Edema disease had herd- and litter-level morbidity rates of 9% and 55.1%, and mortality rates of7 % and 42.8%, respectively. The process of weaning, abrupt feed changes, lack of water, significantly higher gastrointestinal helminths and presence of pathogenic E. coli in healthy animals were risk factors. Edema disease-like syndromes had herd- and litterlevel morbidity rates in ranges of 6.1 -50% and 4.6 - 42.9% and mortality rates in ranges of 10 - 66.7% and 6 -33.3%, respectively. Feeding swill and farm weeds and poor hygiene were additional risk factors for edema disease-like syndromes. This study shows that: (1) edema disease with an prevalence of 39.3% is the most common disease in Kabete region, (2) edema disease-like syndromes encountered in the region include: post weaning diarrhea, chemical poisoning, systemic salmonellosis, streptococcal meningitis among others, (3) a panel of diagnostic techniques that include: clinical and pathological examinations and laboratory analyses are useful in diagnosing edema disease and edema disease-like syndromes, (4) weaning, feed changes, lack of water, heavy worm burdens, presence of pathogenic E. coli in healthy pigs, feeding swill and farm weeds are risk factors for edema disease and edema disease-like syndromes. This study recommends that: (1) diagnostic techniques which include: clinical and post mortem examinations and laboratory analyses for infectious and non-infectious agents be considered in series in diagnosing edema disease and edema disease-like syndromes, (2) awareness be created with stakeholders on the etiological, clinical and pathological presentations of edema disease and edema disease-like syndromes and the risk factors that need to be addressed and (3) that further research be geared towards investigating the causes of the many inconclusively diagnosed cases which could be nutritional deficiencies, gastrointestinal helminthes, infectious agents, among others.