GUIDELINE for Giardiasis

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 authored by Corine Boucraut-Baralon and ABCD colleagues.

Key points

• Giardia is a protozoal parasite that infects the small intestine of cats and can cause diarrhoea.
• The genotypes (assemblages) considered as feline specific do not appear to infect humans, but zoonotic genotypes (isolated from human cases) are frequently found in cats.
• Infection is most common in young cats particularly from multi-cat 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, zinc sulphate flotation of several pooled faecal samples or PCR tests on faecal samples.
• 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. Due to potential appearance of bacterial and parasitic resistance, it is not recommended to treat asymptomatic Giardia-positive cats.

Agent properties

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. Eight different molecular subtypes have been identified designated A-H (table 1). F is the genotype seen in cats whereas A and B are the main genotype in man (Lebbad et al., 2010). Giardiasis was therefore not considered to be a zoonotic infection (Xiao and Fayer, 2008; Ballweber et al., 2010). But numerous studies show that A and B genotypes may be isolated from dogs and cats, in some of them more frequently than F genotype considered as feline-specific.

Table 1. Genetic assemblages Genotypes of Giardia duodenalis infecting different species (revised nomenclature by Thompson and Monis, 2012)

Life cycle

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 trophozoites.

Fig. 1. Life cycle of Giardia intestinalis. ©ABCD, Karin de Lange

Epidemiology

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 been demonstrated that the diagnostic screening test is the most important factor influencing the prevalence rate in a meta-analysis study (Bouzid et al., 2015), but generally a prevalence of 1 to 20% has been reported (Paoletti et al., 2010; Dado et al., 2012; Sotiriadou et al., 2013; Paris et al., 2014; Hinney et al., 2015; Pallant et al., 2015; Piekarska et al., 2016; Gil et al., 2017; Kostopoulou et al., 2017; Vrhovec et al., 2022; De Waal et al., 2023). However, the prevalence in stray cats, shelter and breeding catteries can be much higher than in owned cats (Hinney et al., 2015; de Lucio et al., 2017; Gil et al., 2017; Enemark et al., 2020; Guadano Procesi et al., 2022). In several studies, the prevalence of infection in cats is low compared to the infection rate in dogs (de Lucio et al., 2017; Gil et al., 2017; Sommer et al., 2018). A study from Germany, using an ELISA test detecting coproantigen has shown higher prevalences of respectively 30 and 17% in dogs and cats (Sommer et al., 2018). In another large study in Germany, the prevalence of Giardia in samples of cats sent to a diagnostic laboratory was lower in the more recent period (2015-2017) compared to data from the earlier (2003-2005) period (10.6 % versus 15.4%) (Vrhovec et al., 2022).

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). In different studies, (33 cats from Danish catteries; 528 domestic cats in a feline hospital in Mexico) liquid faeces / diarrhoea were associated with the presence of Giardia (Enemark et al., 2020; Iturbe Cossio et al., 2021). The prevalence has also been demonstrated to be higher in young cats in several studies (Bouzid et al., 2015; Paris et al., 2014; Pallant et al., 2015; Kostopoulou et al., 2017) and in purebred cats in one German study (Pallant et al., 2015). A correlation was also found between Giardia infection and male sex, Cryptosporidium and other parasitic co-infections and cats that had not been dewormed (Enemark et al., 2020).

Table 2. Giardia prevalence and genetic assemblages in European cats

Pathogenesis

In natural and experimental infections, the latent period extends from 10 days to two weeks (Belosevic et al., 1984; Stein et al., 2003). In natural infection, cyst excretion can be intermittent or continuous during the acute phase and most cats eliminate the infection within four to six weeks (Belosevic et al., 1984). In contrast, in experimental infections using a high dose of cysts, most cats remain infected 28 weeks post exposure, although the number of excreted cysts decreased progressively during the course of infection (Stein et al., 2003). Giardia trophozoites attach to the brush border of the villous epithelium and the parasite can cause damage to, and loss of, the epithelial cells of the lower small intestine provoking an inflammatory response (Kirkpatrick, 1987). There may be blunting of the intestinal villi leading to malabsorption.

Immunity

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.

Clinical signs

Young cats are more susceptible to both infection and associated disease, with most clinical infections occurring in cats under one year of age (Bouzid et al., 2015; Pallant et al., 2015; Kostopoulou et al., 2017). Many cases of Giardia infection are not followed by overt disease especially in mature cats (Barr et al., 1994). However, the importance of this parasite as a diarrhoeal pathogen in cats is not clear, with discrepant results between studies. Experimental infections have induced clinical signs, but not in all cases (Stein et al., 2003). Sommer et al. (2018) did not find any correlation in dogs nor cats, although the Giardia prevalence was higher in cats presenting with diarrhoea in other studies (Epe et al., 2010; Paris et al., 2014; Enemark et al., 2020; Iturbe Cossio et al., 2021). The mechanism by which diarrhoea is induced is also not clear, but is thought to be related to malabsorption, which may be accompanied by weight loss, a prominent feature in some cases. The diarrhoea is typically of a small intestinal nature with passage of liquid or semi-liquid faeces but can sometimes show large intestinal features containing mucus/blood. The clinical course of the disease may last for weeks (Belosevic et al., 1984), and chronic giardiasis has been described in immunocompromised cats.

After treatment, secondary gut changes might take some time to resolve; so, diarrhoea can continue for some time after the infection has been eliminated.

Diagnosis

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. Routine saturated salt or sucrose methods are unsatisfactory since they lead to distortion of the cysts. Excretion of cysts is erratic and therefore several (usually three) faecal samples collected on consecutive or alternative days should be screened.

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 Giardia antigen in faeces are available and investigations suggested that the ELISA tests now used are more sensitive than microscopy (Sommer et al., 2018). However, it was suggested previously that ELISA tests are not more sensitive than careful faecal screening (Barr et al., 1992), and several studies confirmed that ELISA and IFA performed better than microscopy (Cirak and Bauer, 2004; Bouzid et al., 2015; Uehlinger et al., 2017). Studies have shown that ELISA detection of antigen correlates well with direct fluorescent antibody screening results (Cirak and Bauer, 2004; Sommer et al., 2018).

PCR tests are available and are used for routine diagnostics. They have the advantage of being able to identify the subtype present. The first PCR-based studies displayed a high proportion of positives (up to 80% versus 60% for ELISA and 5% for microscopy), which raised concerns that they might detect infections that are not clinically relevant (McGlade et al., 2003). More studies have demonstrated the high sensitivity and specificity of PCR (Papini et al., 2013; Uehlinger et al., 2017). Moreover, real-time PCR assays are now available for Giardia detection and several studies showed similar prevalence rates when real-time PCR was compared to other techniques (Yang et al., 2015; Table 2).

The faecal flotation method was the standard test used in the past, but the in-practice ELISA faecal antigen test appears to be equally sensitive and specific and is convenient to perform. Point of Care immunochromatography tests are also available and were demonstrated more sensitive than microscopy (Symeonidou et al., 2020). Examination of faecal smears is cheap and has the advantage of identifying other potential parasites – but it is not popular in practice and is 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.

Treatment

Due to potential appearance of bacterial and parasitic resistance, it is not recommended to treat asymptomatic Giardia-positive cats, especially with metronidazole and fenbendazole.

The standard treatment of Giardia infection has generally been an imidazole, usually fenbendazole given at 50 mg/kg/day for 5-7 days (Barr et al., 1994; Keith et al., 2003). Fenbendazole may be used in pregnant queens. Metronidazole is an alternative, and the original recommendation was to use it at a dosage of 50 mg/kg/day for five days but should not be used in pregnant queens. This dosage carries an increased risk of side effects – central nervous toxicity causing weakness, ataxia, disorientation and seizures. It has been suggested that treatment during 7 days with a daily dosage of 25 mg/kg is effective, which is unlikely to induce side effects (Scorza and Lappin, 2004). 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 the appearance of E. coli antibiotic resistance (Tysnes et al., 2016).

Another alternative treatment is use of ronidazole which has been proved as efficient against Giardiasis in dogs (Fiechter et al., 2012) and in cats (Zanzani et al., 2016). Ronidazole is also currently used as treatment of infection with Tritrichomonas foetus in cats.

Use of a single dose of 50 mg/kg PO of nitazoxanide has been proposed as an alternative for treatment in dogs and shows an efficacy equivalent to 3 doses of fenbendazole (Romano and Lallo, 2023).

It is not recommended to treat an asymptomatic cat, but in multi-cat environments where cats with clinical signs are present, it may be more efficient to treat all animals (dogs and cats) living together (ESCCAP recommendation). Moreover, positive cats living in contact with immunocompromised people should be treated.

Beside treatment, it is critical to manage the environment for preventing super-infection and re-infection along and after the treatment.

Vaccination

A vaccine based on inactivated trophozoites 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.

Prevention and hygiene

In contaminated environments, intensive cleaning and use of 4-chlorine-M-cresol (Chlorocresol) or quaternary ammonium compounds are efficient to avoid re-infection and spread of the infection in a multi-cat house. Faeces from infected animals should be destroyed and bowls and surfaces should be cleaned and disinfected with quaternary ammonium. If possible, moving the cat to another room may also help to avoid re-infection.

Washing/shampooing of animals or at least perianal area with shampoo containing chlorhexidine at the beginning and end of treatment may help to eliminate the cysts.

Testing may be proposed for new cats entering in a multi-cat environment to avoid introduction of the parasite. This can be done during the quarantine.

Care staff (nurses, vets, students of Veterinary Universities…) should be aware about and respect hygiene rules.

Zoonotic risk

Many European studies in different countries or regions (Germany, Italy, Spain, Greece, Poland…) demonstrated the presence of genotype A in cats (Paoletti et al., 2010; Dado et al., 2012; Sotiriadou et al., 2013; Zanzani et al., 2014; Pallant et al., 2015; Piekarska et al., 2016; Kostopoulou et al., 2017; Gil et al., 2017; Guadano Procesi et al., 2022) either alone or as a dual infection (A and F; Dado et al., 2012). Genotype B has also been identified in cats (Pallant et al., 2015; Kostopoulou et al., 2017), but A is most prevalent, according to the different European studies and a Canadian one (McDowall et al., 2011). The risk of harbouring zoonotic Giardia seems to be higher in young cats less than one year of age compared to older cats. The risk is also higher in purebred cats (Pallant et al., 2015) and in stray cats, with 35% testing Giardia positive, most of them due to A assemblage (Guadano Procesi et al., 2022).

No zoonotic assemblages were detected in three Giardia positive dogs and two Giardia positive cats living in the Alava region of Spain, suggesting that household transmission of Giardia by pets, if it occurs, is probably infrequent (de Lucio et al., 2017). 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 tested positive and zoonotic assemblage A in cats was detected in a shelter in the same region (Gil et al., 2017).

On the other hand, a study conducted in children living in poor environmental conditions in Slovakia showed that cat specific assemblage F is present in humans in Europe (Pipikova et al., 2018).

To date no studies have shown direct transmission of Giardia from cats to humans; 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, although there is no proof of direct cat-to-human transmission of Giardia, since zoonotic species are sometimes detected in infected (young) cats, the zoonotic potential of Giardia in cats should be considered where young cats are living with immunocompromised people. Testing these cats is recommended.

Acknowledgement

ABCD Europe gratefully acknowledges the support of Boehringer Ingelheim (the founding sponsor of the ABCD), Virbac and MSD Animal Health.

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