Parasitology. 2017 Jan;144(1):81-94. doi: 10.1017/S0031182015001407.

Knowledge gaps in the epidemiology of Toxocara: the enigma remains.

Holland CV1.

Department of Zoology,School of Natural Sciences,Trinity College,Dublin 2,Ireland.


Toxocara species infect a wide range of companion, domestic and wild animals as definitive and paratenic hosts, via multiple routes of transmission, producing long-lived tissue-inhabiting larvae and resistant eggs that can survive in the external environment. Therefore Toxocara and the disease it causes in humans, toxocariasis, represents an ideal aetiological agent for the development of the one health approach. However, despite increasing awareness of the public health significance of toxocariasis, gaps in our understanding of certain key aspects of the parasite’s biology and epidemiology remain. These gaps hinder our ability to integrate research effort within the veterinary, medical and environmental disciplines. This review will highlight key deficits in our understanding of nine dimensions of Toxocara epidemiology and discuss a potential scenario to develop a more integrated, one health approach to improve our understanding of the prevention and control of this complex and cryptic zoonosis.

KEYWORDS: Toxocara spp.; One health; definitive hosts; environmental contamination; epidemiology; paratenic hosts; toxocariasis

PMID: 26670118



In this paper, I identified significant knowledge gaps in nine dimensions of the epidemiology of toxocariasis [1].  Toxocariasis is a significant zoonotic disease with a worldwide distribution. Despite its ubiquity, it remains a classic neglected disease [2].

The nine knowledge gaps are illustrated in Figure 1 and explained as follows:

  1. The relative importance of sources of infection and the modes of transmission
  2. The role of the veterinarian in the context of a key reservoir of infection (Toxocara in companion animals)
  3. An evaluation of our current knowledge of the significance of the presence of Toxocara eggs on the hair of definitive hosts
  4. Variation in exposure to infection in humans and its relationship with disease
  5. Population-based estimates of eye disease associated with Toxocara
  6. The significance of brain involvement in toxocariasis and the link with cognitive deficits in humans
  7. Improvement in understanding of environmental contamination with Toxocara eggs
  8. The role of non-human paratenic hosts (for example small rodents) in the epidemiology of toxocariasis
  9. The paucity of information on Toxocara cati including its role in human disease



[1] Holland, C.V. (2017). Knowledge gaps in the epidemiology of toxocariasis: the enigma remains. Parasitology  144(1), 81-94.

[2] Holland, C.V. and Smith, H.V. (2006). Toxocara : the enigmatic parasite, 1st Edition, CABI publishing pp 301.