Edited June 2017
The Giardiasis in cats guidelines were published by Tim Gruffydd-Jones et al. in the Journal of Feline Medicine and Surgery 2013, 15, 650-652. This update has been compiled by Corine Boucraut-Baralon.
Giardia is a protozoal parasite that infects the small intestine of cats and can cause diarrhoea. The biotypes considered as feline specific biotypes do not appear to infect humans but zoonotic biotypes (isolated from human cases) are frequently found in cats. Infection is most common in young cats particularly from multicat backgrounds. Infected cats that develop clinical signs show small intestinal diarrhoea and there may be associated weight loss. Diagnosis of infection is usually based on an in practice ELISA for faecal antigen or zinc sulphate flotation of several pooled faecal samples. PCR tests are available but not used so widely. Infection can be detected in clinically healthy cats; so interpretation of a positive result in cats with diarrhoea requires care. Fenbendazole or metronidazole are regarded as the treatments of choice. Secondary gut changes may take some time to resolve; so diarrhoea may continue for some time after infection has been eliminated.
A number of names have been used for the coccidian flagellate protozoan parasite giardia – G. duodenalis (also known as G. lamblia or G. intestinalis). Giardia can infect a number of hosts including man. Seven different molecular subtypes have been identified designated A-G (table 1). F is the subgroup seen in cats whereas A and B are the main subgroups in man (Lebbad et al., 2010). This was therefore not considered to be a zoonotic infection (Xiao and Fayer, 2008; Ballweber et al., 2010). But numerous recent studies show that A and B subtypes may be isolated from dogs and cats, in some of them more frequently than F sub-type considered as feline-specific.
Table 1. Genetic assemblages (Sub-types) of Giardia duodenalis infecting different species (revised nomenclature by Thompson and Monis, 2012)
|Species||Assemblage (species) of Giardia||Other names|
|Human, primates, rodents, dogs, cats, livestock, some wild animals||A, B (except rodents for B) (considered as zoonotic assemblages)||G. intestinalis, G. lamblia, G. duodenalis (A)
G. enteritica (B)
|Dogs, canids||C, D||G. canis|
|Rats (cats)||G||G. simondi|
A recent study failed to detect zoonotic assemblages in 3 Giardia positive dogs and 2 positive cats living in Alava region of Spain, suggesting that household transmission of Giardia by pets if any is probably not frequent. In this study no simultaneous infections in human and canine/feline hosts by G. duodenalis were demonstrated although 29% (16/55) of dogs and 5.9% of cats were detected positive (de Lucio et al., 2017), although a study in a shelter in the same region demonstrated presence of zoonotic assemblage A in cats (Gil et al., 2017).
To date there is no study evidencing direct transmission of Giardia from cats to humans and the main sources of contamination for humans are raw vegetables and water. Moreover the prevalence of Giardia infection in asymptomatic cats is low in most European countries.
However, considering that zoonotic species are frequent in infected (young) cats, the zoonotic potential of Giardia in cats should be considered, especially if cats are living with immunocompromised people.
The parasite has a direct life cycle. It lives in the lower small intestine of the cat in its trophozoite form, adherent to the intestinal wall. It replicates by binary fission to produce the encysted form, which is passed in the faeces in addition to the trophozoites..
Giardia is transmitted by the faecal-oral route. Although trophozoites are excreted in the faeces, these do not survive well in the environment and are unlikely to cause infection. In contrast, cysts are highly infectious and successful transmission requires only a small number to be ingested. The cysts can survive in the environment for up to several months in ideal conditions and indirect transmission via faecal contamination can occur.
Epidemiological studies in different countries, and sampling different cat populations have shown a variable prevalence. It has depended upon the diagnostic screening test used, but generally a prevalence of 1-20% has been reported (Paoletti et al., 2010; Dado et al., 2012; Sotiriadou et al., 2013; Hinney et al., 2015; Pallant et al., 2015; Piekarska et al., 2016; Gil et al., 2017; Kostopoulou et al., 2017). In recent Spanish studies, the prevalence of infection in cats is low comparing to the infection rate in dogs (de Lucio et al., 2017; Gil et al., 2017)
In a meta-analysis study, it has been demonstrated that the prevalence is higher in cats with diarrhoea compared to healthy cats (Bouzid et al., 2015). The prevalence has also been demonstrated to be higher in young cats (Bouzid et al., 2015; Pallant et al., 2015; Kostopoulou et al., 2017) in many studies and in purebred cats in one German study (Pallant et al., 2015). The prevalence in shelters seems to be higher than in owned cats (Hinney et al., 2015; de Lucio et al., 2017; Gil et al., 2017).
The parasite can cause damage to and loss of the epithelial cells of the lower small intestine provoking an inflammatory response. There may be blunting of the intestinal villi leading to malabsorption.
Young cats are more susceptible to both infection and associated disease, with most clinical infections occurring in cats under one year of age. Many cases of Giardia infection are not followed by overt disease, and the importance of this parasite as a diarrhoeal pathogen in cats is not clear. Experimental infections have induced clinical signs, but not in all cases. The mechanism by which diarrhoea is induced is also not clear, but thought to be related to malabsorption, which may be accompanied by weight loss, which is a prominent feature in some cases. The diarrhoea is typically of a small intestinal nature with passage of liquid or semi-liquid faeces but may sometimes show large intestinal features containing mucus/blood. The clinical course of the disease may last for weeks.
The immune response to Giardia infection is poorly understood in cats. Based on information from infection in other species it is presumed that cellular immunity and an IgA response are key to providing protective immunity.
The infection is diagnosed using direct examination of faecal smears (wet mount examination), faecal flotation methods, faecal ELISA antigen assays, direct immunofluorescence on faecal smears and PCR.
Trophozoites can be identified in fresh faecal smears. They are motile with a rolling action. A small amount of freshly passed faeces or mucus is mixed with a drop of saline solution on a microscope slide, covered with a coverslip and immediately examined under a microscope at a magnification of x100. Further examination at x400 allows definitive identification. It is also possible to use microscopic examination of duodenal aspirates collected during endoscopic small intestinal intubation for trophozoites. However, Giardia resides further down the small intestine of cats beyond the reach of endoscopic intubation (McDowall et al., 2011).
A zinc sulphate flotation method is recommended for faecal screening. Excretion of cysts is erratic and therefore several (usually three) faecal samples collected on consecutive or alternative days should be screened. Routine saturated salt or sucrose methods are unsatisfactory since they lead to distortion of the cysts.
It is also possible to use a direct fluorescent antibody technique to detect cysts in faecal smears, a test not widely used in Europe.
ELISA techniques for detecting antigen in faeces are available, including an in-practice SNAP test (IDEXX Ltd.) but do not appear to be more sensitive than careful faecal screening (Barr et al., 1992). Studies have shown that ELISA detection of antigen correlates well with direct fluorescent antibody screening results (Cirak and Bauer, 2004).
PCR tests are available but not widely used. They have the advantage of being able to identify the subtype present. The first PCR-based studies have shown a high proportion of positives (up to 80%) which has raised concerns that they may detect infections that are not clinically relevant (McGlade et al., 2003). However, quantitative real-time PCR assays are now available for Giardia detection and recent studies gave the same prevalence rate than other techniques (Yang et al., 2015).
The faecal flotation method has been the standard test used in the past, but the in-practice faecal antigen test appears to be equally sensitive and specific, and is convenient to perform. Examination of faecal smears is cheap and has the advantage of identifying other potential parasites – but it is not popular in practice and less sensitive (Olson et al., 2010).
A pragmatic approach often used by practitioners as an alternative to testing is to assess the response to treatment. This should be avoided because of the risk of altering the gut flora with antibiotics. Moreover, co-infections with other parasites like Tritrichomonas foetus or Cryptosporidium are frequent and the treatment, if necessary, should be adapted to the results of analyses.
The standard treatment of Giardia infection has generally been an imidazole, usually fenbendazole (Panacur) given at 50 mg/kg for 5-7 days (Barr et al., 1994; Keith et al., 2003). However, metronidazole is an alternative, and the original recommendation was to use it at a dosage of 50 mg/kg for five days. This dosage carries an increased risk of side effects – central nervous toxicity causing weakness, ataxia, disorientation and seizures. Recently it has been suggested that a daily dosage of 25 mg/kg is effective, which is unlikely to induce side effects. In some difficult cases implying many infected cats, a second treatment may be necessary and in that case, combination of fenbendazole and metronidazole may be effective. However, it has been suggested that a second round treatment with fenbendazole may potentiate appearance of E.coli antibiotic resistance (Tysnes et al., 2016).
A vaccine based on inactivated trophozoites (Giardia Vax – Fort Dodge/Pfizer) has been used in the USA but not in Europe and is no longer available. It was used for treatment as well as for prevention.
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