Malaria is the most significant human parasitic disease. It is caused by an intra-erythrocytic Apicomplexa protozoa of Plasmodiidae family and Plasmodium genus. This parasite is transmitted by the bite of an infected female mosquito of Anopheles genus during a blood meal.

While malaria threatens almost half of the world’s population, primarily in Africa and in Asia [1], vector control using insecticide-treated nets (ITNs) and indoor residual spraying (IRS) remain the most effective ways to prevent malaria. Nevertheless, the large use of insecticides over many years has selected several mechanisms of resistance to these [2] in vectors. Other potential environmental strategies such as zooprophylaxis have long been propagated as a promising alternative to the use of insecticides. This concept uses alternative host species such as livestock, to distract malaria vectors away from people, thereby preventing the transmission of malaria to humans [3]. Moreover, different studies have showed a prophylactic effect of livestock such as cattle, donkeys, rabbit and pigs [4] on malaria risk in Papua New Guinea and in Sri Lanka [5] but also in Kenya and Zambia [6], proving that the presence of cattle could be used as a barrier to the spread of malaria [7], [8].

However, increasing zooprophylaxis alternative could increase the phenomenon of zoopotentiation: the presence of livestock may increase malaria transmission to humans [6] by creating additional blood meal sources, therefore, it can increase vector lifespan and population density [9]–[11], as proved by research conducted in Pakistan, the Philippines and Ethiopia showing that the presence of cattle can also be a risk factor for the spread of malaria [5].

Indeed, these concepts are controversial which may be explained for by the variety of analysed livestock species and animal keeping practices, and the associated variable attractiveness for different zoophilic vectors [5], [6]. For instance, zooprophylaxis may more occur where livestock is kept at a distance from human sleeping quarters at night, and where other protective measures are used, whereas zoopotentiation may more take place where livestock is near human sleeping quarters at night and where mosquito species prefer human hosts [12].

Currently, the practical value of zooprophylaxis and the reasons for observed zooprophylactic success remain under debate [5].

To know more about the relationship between the presence of livestock and malaria prevalence in rural endemic areas, researchers from the University of Frankfürt (Germany) in collaboration with the Sriwijaya University (Indonesia), the Nepal Health Research Council (Nepal) as well as the Queen Mary University of London (UK) carried out a scientific investigation in Indonesia where the national average of malaria prevalence grew up from 2.85% in 2007 to 6.0% in 2013 [13], [14] and where the practice of keeping livestock is widely distributed throughout the Indonesian population. Their results are published in Malaria Journal [15].

By making use on dataset from a cross-sectional survey made in 2007 by the Indonesia Basic Health Research (IBHR) [13] including 259,885 research participants of all ages representative who reside in 15 rural Indonesian provinces of highly malaria-endemic (Figure 1), researchers used multivariate logistic regressions to evaluate the influence of the presence of livestock and other independent demographic, social and behavioural variables on the malaria prevalence.

Figure. 1: The proportion of malaria in regencies and cities within rural areas of Indonesian provinces with malaria prevalence above the national average.


(Source: Hasyim et al. 2018 [15])

Via an important set of questionnaires, IBHR interviewed participants about :

  • Raising livestock and/or poultry and/or pets:
    If participants were keeping poultry (chickens, ducks, birds), medium-sized livestock (goats, sheep, and pigs), large-sized livestock (cows, buffaloes, and horses) or pets such as dogs, cats, and rabbits.
    If livestock was kept, then it was noted whether the livestock was kept inside the house or outdoors.
  • Malaria status (if a participant within the past month was ever diagnosed as being malaria-positive by health professionals)
  • Characteristics of participants (gender, age, education, principal occupation)
  • Behaviour (sleep under a mosquito net, use of a net insecticide, defecating habits)
  • Accessibility and utilization of health services (if participants were able to access health services by travelling)
  • Environmental sanitation (type of container/media, sewage canal, sewage canal conditions)
  • Location of cages (medium-sized breeding animals and large-sized breeding animals)

Results showed that the malaria prevalence in these 15 Indonesian rural provinces (3,5%) was higher than the national average in 2007 (2,85%).
According to the survey of IBHR, the majority of participants raises poultry (53,7% of participants) followed by pets (25,2%), medium-sized breeding animals (22.2%), and large-sized breeding animals (10.2%) (Figure 2).

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The survey revealed also that livestock and poultry were more preferably kept outside (Figure 2) with 9.64% of the participants raising large-sized breeding animals, and 20.59% participants raising medium-sized breeding animals outside of the house. Despite this, between 0.52% to 1.63% of participants kept livestock inside the house.

Fig. 2: The proportion of rural population raising livestock (%) and the location of cages (inside the house—white bar, outside the house—grey bar) in highly malaria-endemic endemic areas in 15 provinces of Indonesia.


(Source: Hasyim et al. 2018 [15])

Moreover, data showed that malaria prevalence is increased in the participants raising medium-sized livestock, and more specifically if this type of livestock is keeping inside of the house, even if keeping medium-sized livestock outside also increased the malaria prevalence at a lower level. Indeed, these participants contracted more malaria than those who do not have such animals. However, keeping large-sized breeding animals does not considerably increase malaria prevalence.

This investigation provided evidence for a positive relationship between medium-sized livestock which were kept inside the house and the prevalence of malaria in the human population living in rural, highly malaria endemic areas of Indonesia. Indeed, the presence of medium-sized livestock increased the likelihood of contracting malaria by 2.81 suggesting that the presence of certain livestock types potentiate malaria risk.

These results could be explained by the fact that the presence of livestock increased the abundance of vectors for Plasmodium species as demonstrated in Kenya and in Mozambique, where the increasing abundance of goats or sheep, donkeys and pigs increased the abundance of Anopheles mosquitoes near to houses [4], [16]. Thus, the phenomena of zoopotentiation could occur due to the increasing availability of host selection for certain livestock and therefore, it increases human malaria exposure if the heat and odour cues emitted by animals attract a higher number of vectors to households in or near the area where they are kept [6] but also if the physical disturbances created by animals (e.g., puddles, hoof prints, watering sites) increase the potential for larval habitats and thus adult vector density near households. In this study, the participants who had an open sewage canal were at higher odds of contracting malaria than others, highlighting the importance of potential larval habitats near houses.

Added that, different factors such as social and demographic factors as well as behavioural factors were determinants of malaria status. Among participants, those from 15 to 64 years old, and especially male, contracted malaria significantly more than others. These results remind those found in the Democratic Republic of Congo and in Ethiopia where the malaria prevalence also differed by gender, with men more likely to be parasitaemic than older women [17], [18] but they contrast with those found in Kenya where adult women living in an endemic area are 50% more likely to become infected with malaria parasites than men [19].

In addition, the proximity of health facilities, as well as the fact to use open or closed sewage system, influenced the malaria prevalence. Indeed, most participants who needed to travel more than sixty minutes to access to health facilities were more susceptible to contract malaria than participants who were able to access faster to health services. Also, most of the participants who used open sewage systems at home and those without a sewage system are at higher odds of contracting the disease than those who have closed sewage systems.

Furthermore, participants who adopted protective behaviour against mosquito using ITNs and mosquito nets significantly decreased the risk to contract this infectious disease in these highly endemic areas of Indonesia.

However, this study has some limitations. First of all, the short period of clinical diagnosis of malaria by retrospective interview may underestimate malaria positive respondents and should be increased. Finally, other factors could influence the malaria prevalence, such as the ecology (species, behaviour…) of different Anopheles species [20] and could help to better understand the malaria transmission to develop appropriate vector control strategies.

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Anyway, the main recommendation from this study is to keep the medium-sized livestock outside of the house.

Thanks for reading.

And don’t forget: Fight Malaria!

Bibliography

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[16] E. A. Temu, M. Coleman, A. P. Abilio, and I. Kleinschmidt, “High Prevalence of Malaria in Zambezia, Mozambique: The Protective Effect of IRS versus Increased Risks Due to Pig-Keeping and House Construction,” PLoS One, vol. 7, no. 2, p. e31409, Feb. 2012.

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