Bovine coccidiosis is a common parasitic disease that can result in significant economic losses (Mundt et al., 2005). In more intensive cattle raising areas it can present a major challenge in raising young stock (Bangoura & Bardsley, 2020) but is not common in more extensive Southern Australian beef grazing systems. In Australian cattle there are two pathogenic species of Eimeria; Eimeria zuernii and E. bovis (Keeton & Navarre, 2018).
Coccidiosis is most commonly seen in calves between 3 and 8 months of age (Bangoura and Bardsley, 2020; Parkinson et al., 2019). In younger calves, diarrhoea is usually caused by other pathogens, including rotavirus, coronavirus, Escherichia coli, Salmonella and Cryptosporidium (Philippe et al., 2014). The following cases document an unusual presentation of coccidiosis, causing sporadic sudden death in nursing beef calves at 8-10 weeks of age.
Case 1: On 25 October 2018 an Angus heifer calf was found dead in a mob of 100 cows. The case presented on a beef property southwest of Bathurst running 1000 breeding Angus cows. In the week prior, two calves approximately 8 weeks old, had died in a mob of 100 heifers. These calves had been marked and vaccinated with 7-in-1 just over a month prior to death and received the vaccine booster the same week they were found dead. The calf found dead on the date of investigation was 8-10 weeks old and had been marked and vaccinated with 7-in-1 10 days prior to death.
Case 2: Almost a year later, a property southwest of Lithgow on the Central Tablelands of NSW reported the sudden death of an 8-week-old Angus bull calf. This producer runs a herd of 370 Angus cows on improved phalaris, cocksfoot, subterranean clover pastures. On 26 September 2019, the calf was found dead in a mob of 35 cows. The calf was 8 weeks old and was not marked or vaccinated. The remainder of the mob were observed to be in good condition.
Both calves were necropsied. Case 1 was a well grown heifer calf with marked enophthalmos. There was mild hepatomegaly noted. The small intestinal contents were pasty yellow. The colonic and rectal contents however, were dark red with a strawberry jam consistency. Differential diagnoses considered for this heifer calf were coccidiosis, cryptosporidiosis and salmonellosis.
Case 2 was a well grown bull calf, with external findings of bilateral enophthalmos, pale mucous membranes and dried, dark, crusted bloody faeces covering the perineum. The caecum and colon had multifocal, large, ecchymotic, serosal haemorrhages. The large intestinal contents were thick and dark red, and an intraluminal blood clot, 5cm in diameter, extended for 25cm from the caecum to the colon. There were large haemorrhages covering the serosa of the rumen, with no abnormalities detected in the abomasum or small intestine. Differential diagnoses considered included salmonellosis and coccidiosis.
Figure 4. Case 2: Enophthalmos indicating marked dehydration (image by Bruce Watt 2019)
Mild, subacute, diffuse, lymphocytic enteritis. There was congestion of blood vessels within the small intestine and the crypts contained diffuse mucin / proteinaceous material. The large intestinal sample revealed a marked, subacute, diffuse, lymphoplasmacytic colitis. The colon lamina propria contained moderate intra- and extracellular coccidian macro- and microgamonts, schizonts, trophozoites and oocysts.
Bacteriology / Virology
Samples of colon and bile in selective enrichment culture were negative for Salmonella spp. Colon content samples were negative for E. coli K99 attachment factor, Cryptosporidium spp. and rotavirus on calf enteric ELISA strip test (DipFit bovine Rotavirus, DipFit E coli F5 (K99) and DipFit Cryptosporidium sp, Bio-X Diagnostics S.A.).
A rectal faecal sample was assessed using wet preparation and microscopic examination. The sample was positive (+++) for coccidia indicating a high coccidian burden.
The intestinal samples revealed a necrohaemorrhagic colitis with oedema and large numbers of protozoal organisms consistent with coccidia (macrogamonts, microgamonts, schizonts and oocysts). Multifocally within some areas of large intestine, there were aggregates of extracellular bacteria adherent to superficial cellular debris. Within the liver, there was a sinus leukocytosis and mild to moderate, lymphoplasmacytic, periportal hepatitis.
Bacteriology / Virology
Pooled samples of lymph node and rectal, large intestinal and gall bladder content in selective enrichment culture were negative for Salmonella spp. Rectal content samples were negative for Cryptosporidium spp. and rotavirus on calf enteric ELISA strip test (DipFit bovine Rotavirus, and DipFit Cryptosporidium sp, Bio-X Diagnostics S.A.).
A modified McMaster faecal egg count on large intestinal and rectal contents was negative for coccidia and found no nematode eggs.
It is common for ruminants to be infected with coccidia during their life, with these protozoan parasites co-existing in some animals (Taylor, 2000). Clinical disease occurs if the animals are exposed to high environmental challenge with heavy infestation, or if their resistance is lowered by stress, poor nutrition, or severe concurrent disease (Parkinson et al., 2019).
Adult cattle are generally immune to coccidiosis, serving as carriers of the parasite and contributing towards environmental contamination (Reynolds, 2014). They can develop clinical signs of disease when overwhelmed with stressors (Zechner et al., 2015). Coccidiosis is generally a disease of young animals and is routinely diagnosed at weaning, between the ages of 3-8 months. (Parkinson et al., 2019). This may be because of the stressors experienced at weaning, including change in diet, movement through yards into different paddocks and possibly overcrowding (Bangoura & Bardsley, 2020). The calves in these cases were un-weaned and 8-10 weeks old. Case 1 had exposure to stress during marking, however case 2 was a sudden death with no prior stressors or history to suggest coccidiosis. Cases of coccidiosis have been reported in dairy calves as young as 4 weeks old. Typically, the rate of clinical disease in a coccidiosis outbreak is 5-10% (Parkinson et al., 2019). Therefore, these cases of isolated sudden death in pre-weaned beef calves are unusual presentations.
Coccidia invading the large intestine cause more pathological changes than they would in the small intestine, due to the large intestine’s decreased length and decreased cellular turnover (Taylor, 2000). If many oocysts are ingested over a short period of time, there is no compensation from other regions of the gastrointestinal system. The severity of infection relates to the number of oocysts ingested (Keeton & Navarre, 2018). The calves in these cases presumably ingested an overwhelming number of oocysts to cause peracute disease. Invasion of the large intestine results in reduction of the surface area available for nutrient and water resorption by destroying the villous architecture and decreasing the brush border epithelium height (Philippe et al., 2014). This leads to malabsorptive diarrhoea and other clinical signs of anorexia, lethargy, dehydration and tenesmus (Parkinson et al., 2019). Extensive epithelial destruction along the intestinal tract leads to haemorrhage and diphtheritic enteritis. Therefore, melaena, frank blood, large clots, and epithelial lining are typically present in the diarrhoea. The haemorrhage can be severe enough to cause anaemia and hypovolaemic / haemorrhagic shock. These signs were observed on post-mortem examination of the calves in both cases. Haemorrhagic diarrhoea only occurs with infection of E. bovis and E. zuernii (Bangoura & Bardsley, 2020). Infection with other species of Eimeria tend not to cause severe disease. Diarrhoea may not be the presenting sign (Parkinson et al., 2019). If an animal survives clinical coccidiosis, recovery begins 7-10 days post infection and the intestine will undergo some repair (Parkinson et al., 2019). However, permanent scarring and damage to the intestine may lead to poor growth and decreased feed efficiency (Keeton & Navarre, 2018).
Case 2 was negative on faecal flotation for coccidial oocysts despite protozoal organisms consistent with coccidia (including immature stages and lesser numbers of oocysts) being observed in histopathology sections. In acute clinical cases of severe coccidiosis in cattle, the faecal egg count may be negative for oocysts. This is because most of the destruction to the intestine occurs during schizogony, the asexual stage, prior to gametogony, the stage of sexual reproduction and production of oocysts (Bangoura & Bardsley, 2020).
Treatment of clinically diseased animals with anti-coccidial products may not be effective (Bangoura & Bardsley, 2020). Coccidiostats such as amprolium inhibit the development of internal coccidia stages whereas coccidiocidal drugs (for example toltrazuril) kill the parasites. These anti-coccidial products have little effect on the established infection and later stages of the life cycle (Parkinson et al., 2019).
Following diagnosis, case 1 was referred to a private veterinarian to discuss treatment options. However, no further cases were seen on either property.