A post over at Effect Measure last week reported on this CDC study, which details an outbreak of H1N1 flu amongst the giant anteater (Myremecophaga tridactyla) at the Nashville Zoo.
This caught my attention, because part of my honors thesis involved observing giant anteaters at the Montgomery Zoo. After spending hours and hours a day recording their every movement for an entire summer, I became a little bit attached to them, even though this species was not the main focus of my research. (That portion of my thesis focused on how the activity budget and exhibit utilization of the maned wolf, Chrysocyon brachyurus, changes when sharing an enclosure with another species).
These guys are one of the true oddballs in the mammal world. They lack teeth, able to eschew oral mastication because of the presence of hard growths further along their digestive tract, aided by sand and small rocks that are often found in their stomachs. Most mammals using gastroliths to help digestion are marine (otters, whales, etc), so the giant anteater represents a completely independent evolution of the feature. They are famous for their incredibly long tongues (perfect examples of convergent evolution with other ant-specialists such as the aardvark, pangolin, and some bat species), and they have the endearing habit of carrying their babies around piggy-back style.
In my observations at the zoo, I was also struck by the extreme, um, lack of intelligence of this animal. It was astonishing, really. I would watch the zookeepers try to get the Montgomery anteater onto the exhibit each morning, and sometimes it would take over 30 minutes for it to move 12 feet from its holding pen through the door to the enclosure, because it would just wander around in corners, lost in whatever passes for anteater thoughts, I suppose, even though its breakfast lay on the other side of the door. This was after it had been going through the same routine for three years. Apparently, for M. tridactyla, each morning is a clean slate. This is entirely anecdotal, of course. I am not aware of any studies that have been done on anteater cognition, but their cranial capacity to body size ratio is quite low. Their body temperature is also quite low, which can sometimes correlate to “intelligence” in mammals (how to actually define intelligence is way off-topic and out of the scope of this post, unfortunately).
So, that’s a brief sample of why the giant anteater is interesting, but the recent news makes it even more intriguing. The CDC reports that H1N1 virus was cultured from samples of nasal discharge, which was collected from the animals in February. This strain appears to be closely related to the human H1N1 virus that bloomed around the country during that time. Two of the three animals showed seroconversion (evidence of infection, most often referred to in the context of HIV infection), and the third “appeared to have been exposed to and infected with influenza virus a year before the described outbreak.”
As for the differences between the anteater and human strains, the report states that they were not functionally or antigenically significant, and that the most likely scenario is that the anteaters acquired the virus from exposure to human caretakers. They were unable to tell whether the virus spread from one animal to the next, or if each individual contracted the virus from the caretakers independently.
This is all very intriguing. Apparently no other species at the zoo showed signs of contracting the virus, so what was it about the anteaters that made them susceptible? One would assume that primates might be most vulnerable to contracting a human virus, but that’s not always the case, of course. I’m not sure if there are any boar or other swine species at the Nashville Zoo, but I’m sure there are other perissodactyls, none of which contracted whatever the people were carrying. Most zookeepers do not tend to a single exhibit, especially for animals as low-maintenance as the anteaters, so I can’t imagine that these animals were just unlucky enough to have the only virus-carrying keepers in the entire zoo. The anteaters have such a low body temperature compared to other animals, it seems that the habitat they provide for pathogens may be much different.
All of this is an important reminder of why zoological monitoring is crucial for the management of disease outbreaks, in addition to human and public health measures, for both the flu and other circulating pathogens. Even if a virus jumps to a species that is a low-risk carrier (how many people are exposed to giant anteaters on a regular basis), such incidents can provide critical clues as to the nature of a virus and its ongoing evolution.
