Various species of Giardia have been incriminated as causing disease in cattle. This gut parasite causes scours in calves and can cause diarrhea in adult cattle worldwide. Prevalence rates approach 100% in some herds.
The most frequently isolated species include G. duodenalis (syn G. intestinalis, G lamblia) with a wide mammalian host range. Molecular characterization has revealed that G. duodenalis comprises 7 assemblages (A to G). Assemblage E. G. duodenalis is highly prevalent in cattle herds and Assemblage A in calves is a potential public health concern.
Flagellate protozoa (trophozoites) inhabit the mucosal surfaces of the small intestine, where they attach to the brush border, absorb nutrients, and multiply by binary fission. Trophozoites encyst in the small or large intestine and the newly formed cysts pass in the feces. The prepatent period is generally 3–10 days. Cyst shedding may be continuous over several days and weeks but is often intermittent, especially in the chronic phase of infection. The cyst is the infective stage, and can survive for several weeks in the environment, whereas trophozoites cannot.
Transmission occurs by the fecal-oral route, either by direct contact with an infected host or through a contaminated environment. Characteristics that facilitate infection include the high excretion of cysts by infected animals and the low dose needed for infection. Furthermore, Giardia cysts are infectious immediately upon excretion and very resistant, resulting in a gradual increase in environmental infection pressure. High humidity facilitates survival of cysts in the environment, and overcrowding favors transmission.
Giardia infections in calves can result in scours that does not respond to antibiotic or coccidiostatic treatment. In severe cases, tenesmus and bloody stools may be observed. This disease rarely causes fatal illness compared with other causes of calf scours.
Although trophozoites can occasionally be viewed under light miscroscopy, accurate detection requires ELISA, IFA or PCR testing.
Antiprotozoal drugs have been effective, including Fenbendazole (given at 50 mg/kg/day for 3 days) and albendazole (5–20 mg/kg/day for 3 days). Paromomycin (50–75 mg/kg, PO, for 5 days) was found to be highly efficacious in calves.
- Paz e Silva FM et al (2012) Genetic characterisation of Giardia duodenalis in dairy cattle in Brazil. Folia Parasitol (Praha) 59(1):15-20
- Uehlinger FD et al (2011) Prevalence and genotypes of Giardia duodenalis in dairy and beef cattle in farms around Charlottetown, Prince Edward Island, Canada. Can Vet J 52(9):967-972
- Mark-Carew MP et al (2012) Prevalence of Giardia duodenalis assemblages among dairy herds in the New York City Watershed. Vet Parasitol 185(2-4):151-157
- Budu-Amoako E et al (2012) Occurrence of Cryptosporidium and Giardia on beef farms and water sources within the vicinity of the farms on Prince Edward Island, Canada. Vet Parasitol 184(1):1-9
- Budu-Amoako E et al (2012) Giardia and Cryptosporidium on dairy farms and the role these farms may play in contaminating water sources in Prince Edward Island, Canada. J Vet Intern Med 26(3):668-673