Despite parasite danger, dogs running loose are common, survey finds

A study recently released by the Universidad Nacional’s veterinary school found evidence of dog parasites in all parks surveyed around the San José metropolitan area. Fully 84 percent of dog fecal samples tested had signs. Blood samples from leashed dogs showed high prevalence of antibodies though those remain even after successful treatment in both dogs and people.

The dog roundworm Toxocara is the most dangerous for people and can be picked up by children when the larvae are viable in soil where dogs have defecated. The eggs take a few weeks to develop the earliest stage larvae and then can wait long periods for the opportunity to infect another dog. Humans are incidental hosts, and the larvae do not develop into adult worms to reproduce. However, the larvae can do significant damage either by colonizing the liver or, if one works its way into an eye, it can damage vision and even result in blindness.

Ancylostoma hookworms make up the largest part of the dog parasite load but are rarely able to infect humans. They can however cause severe itching and secondary infections while burrowing into the skin.

Responsible pet owners clean up after their dogs and reduce the presence of parasites. But that is not the case with dogs that run free, either all the time or just when owners let them outside.

As part of data collection for an eventual study, a population survey of free-range dogs is underway. Starting near San Isidro de Heredia, observers travel 10 kilometers most mornings to Los Angeles, to central Santo Domingo and to Santo Tomas de Santo Domingo.

They count the number of loose dogs and note the conditions.

Data are for 62 days from Sept. 2, 2014, through March 27, 2015, interrupted by vacations, weekends and other unplanned developments. Over that period the average per day is 11.4 dogs sighted, or slightly more than one loose animal per kilometer. The range of three to 24 for the same route indicates there is a circulating population and that surveying from a moving car is not the most precise  methodology. For example, the two-kilometer segment freerangedog040615through  Los Angeles where observation is the easiest can produce zero to six in any visit, suggesting that a fair number are inside at any moment or otherwise out of view.

This is mostly a well-off area, and obviously sick or parasite-ridden individuals are noted and registered as such but are not common. Ripped open garbage bags are also recorded, but while a nuisance for solid waste collection, these are not much of a health hazard. Speculation by workers at the Servicio Nacional de Salud Anima that there are a million stray dogs in the country and that their situation as individuals is dire would not seem to be supported here.

Anecdotally, that appears not to be the situation. Most of these dogs are at least loosely associated with one or more households and are not stray. Males outnumber females at least 10 to one, as Costa Ricans think males make better watchdogs. Obviously lactating females are a rare sight.

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