As the Veterinary Officer in Dublin City Council, you are asked to explain to the general public, the public health risks associated with cat feces in public places
Introduction
The Litter Pollution Act 1997, Section 22, enforces the law regarding dog soiling in public areas. These laws are enforced by Dublin City Council’s Litter Warden and failure of compliance can lead to hefty fines and a possible court summons. In conjunction, various campaigns such as the ‘Anti-dog fouling awareness campaign’ are undertaken to increase awareness of the risks associated with dog fouling in public areas. Although much effort is put into protecting public areas from dog feces, the same measures are unfortunately not available regarding the fecal material of cats. This is undoubtedly partly due to the uncontrolled massive density of cats, however, there are nonetheless a plethora of risks associated with this material and it is empirical that the public is aware of these risks. Recent studies by (Szwabe and Blaszkowska, 2017) actually revealed that the potential reservoir of zoonotic parasites in stray cats was of more significance than that of the dog population.
Public areas, especially in urban locations are undeniably seen as commercial litterboxes for all felines and this is very difficult to control. Sandy areas are preferred as in the wild they used these sand-based areas due to the ease of burial. As a result of this, children’s sandboxes and outdoor play areas are the optimal locations for cats to deposit their waste. This has resulted in parents being very concerned and reluctant to let their children play in public parks. Whilst children are most likely to be exposed, they are also one of the most susceptible to infection. Other individuals at high risk of infection would include the elderly and immunosuppressed individuals, for example, chemotherapy patients or pregnant women, however, the likelihood of exposure to these individuals is much less.
In this presentation, I would like to inform you of what I feel are the main public health risks associated with the accumulating load of cat feces in public places. Infections can be broadly categorized as protozoal, helminthic, and bacterial.
Infectious Zoonotic Agents
1. Toxoplasma
Toxoplasma is by far the most important zoonotic agent excreted in the feces of cats. Cats are known as the final host and ingest oocysts in the environment accidentally or by ingesting a previously infected intermediate host. The cat will not show any clinical signs of disease but will nonetheless excrete 2-20 million oocysts per day for up to three weeks. Young children and pregnant women have the most extreme adverse effects following accidental ingestion of the oocysts. While most clinical signs are associated with that flu-like symptoms, muscle aches, fever, and headaches, studies suggest the occurrence of sub-acute meningoencephalitis, encephalopathy, or space-occupying lesions in immunocompromised individuals (Glaser, Angulo, and Rooney, 1994).
Pregnant women who get infected may miscarry, have a stillbirth, or have a congenitally affected child born with birth defects. Recent studies have shown that there is a possible correlation between individuals infected with Toxoplasma and those suffering from mental health issues such as Schizophrenia (Yolken, Dickerson, and Fuller Torrey, 2009). There have also been studies revealing a possible relationship between Parkinson’s disease which is a severe neurodegenerative disease and this protozoan parasite (Miman et al., 2010). In 2006 a terrible tragedy occurred in Letterkenny where a seven-year-old girl died following cardiac failure, which on postmortem was attributable to Toxoplasma.
2. Cryptosporidium
Cryptosporidium is another protozoan parasite passed in the feces of cats and transmitted to humans via direct or indirect contact. General malaise, diarrhea, vomiting, fever, abdominal cramps, and dehydration are just some of the general clinical signs seen both in cats and humans. Although not an infectious agent to ignore, recent genotyping studies have revealed there is a minimal risk of zoonotic transmission as they have demonstrated that Cryptosporidium in cats is caused by a host-specific C. felis whilst in humans C. felis is only responsible for a small number of disease cases (Lucio-Forster et al., 2010).
3. Giardia
Giardia is regarded as being highly significant in certain counties around the world. Environmentally resistant cysts which can survive harsh weather conditions for months are voided in the feces of domestic pets which allows for transmission via direct contact or indirectly via important vehicles such as food and water. Clinical consequences in pets appear minimal, however, there is much more speculation about the public health significance of this disease (Palmer, 1998). There are strong connecting links between morbidity and also severe growth and developmental retardation in affected children (Farthing et al., 2002). The only Giardia species recognized in cats is G. duodenalis otherwise known as G. intestinalis or G. lamblia (Swan and Thompson, 1986), this is the specie that also causes disease in humans.
4. Toxocara
Toxocara cati is a nematode parasite of the small intestines of cats. It has the potential to be zoonotic via fecal-oral transmission and is regarded as ‘an underestimated zoonotic agent’ (Fisher, 2003). Despite the wide availability of highly effective anthelmintics, human toxocariasis is still undoubtedly a hazardous problem (Overgaauw and van Knapen, 2019). The larvae can migrate causing visceral or ocular larva migrans (Eberhard and Alfano, 1998). Visceral larva migrans can involve the abdominal organs, the liver, or the central nervous systems whilst ocular migrans causes visual disturbances, abnormal eye movements, and discomfort.
5. Ancylostoma
Although mainly occurring in tropical and subtropical regions, the public should be aware of the potential pathogenicity associated with hookworm, Ancylostoma. Infection occurs via contact with an environment soiled with hookworm larvae from an infected feline. The larvae penetrate the skin causing cutaneous larva migrans otherwise known as itchy skin disease. The pruritus normally subsides within a few weeks, however, (Robertson, 2000) concluded that with a massive larval burden, there may be penetration to deeper tissues resulting in pulmonary and intestinal symptoms. Protein malnutrition and iron deficiency anemia are common issues within the infected children population while adverse fetal-maternal outcomes can occur in infected pregnant women left untreated (Crompton, 2000).
6. Salmonella
Whilst most Salmonellosis infections are considered to be associated with undercooked chicken and eggs, Salmonella can also be carried asymptomatically by cats and passed in stool with the ability to cause infection in humans. Clinical signs are similar to that caused by other routes of transmission and include diarrhea, nausea, and fever. While studies carried out by (Immerseel, 2004), concluded that healthy household cats are generally safe concerning the transmission of Salmonella to humans unless receiving medications that would result in immune deficiencies, the study, did not account for free-roaming cats who are possibly the main contributors to the public area pollution.
7. Campylobacter
Infected cat stool is undoubtedly a source of Campylobacter infection which in humans generally causes diarrhea which may be bloody, fever, and abdominal cramps. The inadvertent ingestion of cat feces is the route by which humans get infected. Campylobacter infection in pregnant women is of major concern as the transplacental transmission may result in abortion or the onset of premature labor (Simor, 1990) or enteritis and meningitis of the neonate (Gribble, 1981).
It is important to realize that the risk of disease is not the same for all organisms or for all individuals. Because not every infective agent has the same probability of being present or producing the same severity of illness, it is important to view these diseases on a risk-based approach. Without this approach, we would have to assume that every hazardous agent is present in every stool and that each agent causes the same degree of illness but instead we can look at the likelihood of an agent being present and concurrently the severity of the disease that would be present. (Stull, Brophy, and Weese, 2015) viewed the zoonotic agents in such terms and assessed the exposure likelihood and consequences to exposure in individuals who were in some way immunocompromised some of which are presented in the table above. Campylobacter was found to be highly prevalent in the feces of pets and therefore the probability of someone being exposed is exceptionally high. The disease caused by campylobacter is however of low severity in even high-risk individuals and therefore a medium-risk characterization would be considered.
Prevention and Take-Home Messages
Apart from Ancylostoma, the feline fecal pathogens listed above are transmitted to humans via the fecal-oral route.
There is often a misconception that only fresh pet feces pose a risk to human health. Although this may be true for certain agents, a general assumption should not be made as important zoonotic agents such as Toxoplasma oocysts only become infectious following a period of one to five days in the environment. Following excretion, Giardia cysts are immediately infective to humans, however, they can remain viable in the environment for months despite warm, cold, or wet weather.
Many articles such as that by (Beeler and May 2011), emphasize the general ways to prevent feline zoonotic disease transmission. The mechanisms recommended, however, generally apply to household cats as they emphasize the importance of optimizing the health status of the cat, protecting areas from wildlife, and also the daily discarding of stools.
In light of general public areas, the above measures will often not completely eradicate the problem given the fact that the current feral cat population is in the range of 20,000, a number which is rapidly expanding.
Optimum personnel hygiene is likely of greatest importance on the larger scale of things. Following any rummaging in the environment, hands must be thoroughly washed. The hand washing of children is advised to be supervised up to and including the age of five (Stull, Brophy, and Weese, 2015). Wounds should also be covered by plasters and optimally by gloves.
As a general public, we ourselves should share the responsibility of keeping our environment clean and as a knock-on effect, we will prevent the occurrence of zoonotic diseases associated with feline feces. The main issue with starting a campaign like this is that not many people will willingly give their time to clean up faeces from an animal that does not belong to them. Small tasks that could really make a difference include the covering of sandboxes when not in use and the reporting of outbreaks to highlight potential high-risk locations. The creation of shelters for stray cats could provide veterinary care and improve health status. Mass sterilization could help to reduce the increasing breeding problem. Eliminating the problem of abandoned animals would reduce the stray cat population also.
References
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