Update: 99 Households study: wildlife component

As we approach the final quarter of the 99 household study, it is a pleasure to be asked to reflect on the wildlife sampling component of this study. The wildlife sampling team has come a long way since its inception in September 2015, when we were all relative novices in trapping Nairobi’s diverse array of wildlife species. We have had some long days and sleepless nights, but to their credit, the enthusiasm of those involved has never waivered.

A typical day for the wildlife team starts at 5am, when we embark on bird sampling. To ensure we follow best practice for all of our trapping we collaborate with experts at the National Museums of Kenya, and in the mornings Titus Imboma (an ornithologist from the museums) helps us set up an array of mist nets, aimed at trapping birds as they fly in proximity to the household and livestock-keeping areas of each compound. Once caught, each bird is placed in a paper bag to collect a faecal sample, before a number of other body measurements and biological samples are collected. Such opportunistic sampling is a common philosophy among wildlife disease ecologists, and additional samples provide an important resource for future epidemiological work. We next check the rodent traps – we use live-capture Sherman traps which are set throughout the house, livestock-keeping facilities and the household compound. Any rodents that we catch are transported back to the lab at ILRI, where they are humanely euthanized and subjected to a post-mortem examination (PME). This procedure is used to permit the collection of fresh faeces and organ samples which are stored frozen and in formalin. The latter ensures that tissues from these animals are preserved for histopathological interpretation, should the need arise in the future. As dusk settles over Nairobi, the sampling team heads back to the house to trap bats.

The techniques used to trap bats are vey similar to those for birds; very fine mist nets are suspended between fly-ways where bats seek their food (either insects or fruit depending on the species of bat). Due to their propensity to bite, bats present a challenge to remove from the nets and restrain during sampling, but with the appropriate techniques and equipment (i.e. tough gloves!) they can be safely held to collect measurements and samples. We sacrifice a maximum of two bats each night, which are taken back to the lab at ILRI for PME. The rest are sampled live, and released unharmed. When we encounter a bird or bat roost, we use tarpaulins spread underneath the roost in order to collect pooled faecal samples representative of the individual animals using the roost.

Something that has become evident as we move from house-to-house, navigating Nairobi’s  maze of leafy suburbs, high-rise apartments and river-side slums, is the shear diversity of wildlife habitat present in this city. This is reflected in the number of species (birds, rodents, bats, primates and carnivores) we have sampled to date (see table 1). All of these species inhabit different ecological niches which likely govern their levels of interaction with humans and livestock; as an example one would expect very different levels of interaction between house rats that scavenge on animal feed and sunbirds that rely on nectar. How this translates to the risk of disease transmission is something we hope to shed light on by studying the genetic diversity of E. coli in these wildlife, and comparing it to those from humans, livestock and the
environment.

Article By James Hassell

This blog entry is an article on our quarterly Urban Zoo Newsletter Volume 3 Issue 3 which can be accessed by clicking here.