MRSA in humans and animals in Kenya (an overview)

Introduction

Staphylococcus aureus is an important bacteria because of its ability to cause a wide range of diseases and adapt to diverse environments. The bacteria causes infection to both humans and animals by colonizing their skin, skin glands and mucous membranes, resulting to septicemia, meningitis, and arthritis in man and mastitis in the bovine, as well as poultry limb infections [1]. Methicillin-resistant Staphylococcus aureus (MRSA) is a type of staphyloccocal bacteria that is resistant to beta-lactams. It is a common cause of healthcare-associated infections in both developed and developing countries, though limited information is available from the latter [2] [3].

MRSA Resistance mechanisms

The resistance of S. aureus against methicillin is caused by expression of Penicillin binding protein 2A (PBP2A) encoded by the mecA gene [4]. PBP2A has low affinity for beta-lactam antibiotics such as amoxicillin, methicillin and oxacillin, rendering these antibiotics ineffective in treating infections caused by Staphylococcus aureus. Lately, a new methicillin resistance mechanism gene, mecC has been reported in isolates from humans and animals [5]. This therefore means that MRSA is not only associated with prior exposure to a health care facility but also raises concerns for infections originating from the community and veterinary species, and there is a possibility of a cross-infection with animals being potential sources of MRSA infection to humans [6].

MRSA the Kenyan perspective

In 1997, documented rates of MRSA in Kenya were 28 percent of all S. aureus tested in city hospitals. A separate hospital-based study during the same year found the prevalence of MRSA to be 40 percent of all S. aureus infections. In 2006, MRSA was found in 33 percent of S. aureus isolates at another hospital based study [2]. Resistance, therefore, may indicate illegal use of drugs by the public. A survey of farmers in Kenya found that the majority conflated treatment with prevention, effectively replacing hygiene and feeding practices as standard disease prevention with disease treatment [2]. Patterns of resistant Staphylococcus aureus in cattle imply a significant difference in resistance profiles of large and small scale farms, with smaller producers using nearly twice the amount of antibiotics per animal compared with larger producers [7]. The prevalence of multidrug resistance, at 34 percent on small farms, was likewise almost double the rate found at large farms [2].

The dillemma

There is evidence that MRSA infection increases the risk of mortality, morbidity, medical care costs and loss of productivity. The increased medical care costs accrued directly as expenses caused by extension of hospital stay, additional diagnostic or therapeutic procedures, and additional antibiotic use while loss of productivity is due to absence from work during hospitalization. At the same time, published data  concerning  the  antibiotic  susceptibility  patterns  of  MRSA  in  sub-Saharan  Africa  are extremely limited, and few studies on it have been conducted in Kenya [2] [3]. Many studies on MRSA in Kenya are mainly cross-sectional with a focus to determine the prevalence, identifying the antibiotic resistance but they have not focused on the zoonotic significance of MRSA. There is need to understand on how the resistance to MRSA is changing over time so as to be able to clearly visualize the mechanism and transfer of resistance genes in the population [3].

Zoonotic directionality of resistance

It is therefore important not only to determine the antibiotic resistance, but also determine what and who is causing this resistance in humans and animals belonging to the same household and also determine the temporal and spatial change of this resistance over time. This is because, by understanding the dynamics and the epidemiology of MRSA infection over time it will be possible to develop more informed prevention and control strategies, develop more sound policies including education on the rational use of antibiotics to the public.  At the same time it is important to  fill the knowledge gap [3] (especially from a developing country setting) in the zoonotic directionality of MRSA.

References 

Waldvogel, F.A., Staphylococcus aureus, in Principles and practices of infectious disease, G.L. Mandell, D. R.G., and B. J.E., Editors. 2000, Pennsylvania, USA.: Churchill Livingstone, Philadelphia, . p. 1754-1777.

Global Antibiotic Resistance Partnership-Kenya Working Group, Situation Analysis and Recommendations: Antibiotic Use and Resistance in Kenya, S. Kariuki, Editor. 2011, Center for Disease Dynamics, Economics & Policy: Washington, DC and New Delhi.

WHO, Antimicrobial resistance global report on surveillance. 2014. p. 1-256.

Wielders, C.L.C., et al., mecA Gene Is Widely Disseminated in Staphylococcus aureus Population. J. Clin. Microbiol., 2002. 40(11): p. 3970-3975.

Paterson, G.K., et al., The newly described mecA homologue, mecALGA251, is present in methicillin-resistant Staphylococcus aureus isolates from a diverse range of host species. J. Antimicrob. Chemother., 2012. 67(12): p. 2809-2813.

Ferreira, J.P., et al., Transmission of MRSA between Companion Animals and Infected Human Patients Presenting to Outpatient Medical Care Facilities. PLoS ONE, 2011. 6(11): p. e26978.

Shitandi, A. and A. Sternesjö, Prevalence of Multidrug Resistant Staphylococcus aureus in Milk from Large and Small Scale Producers in Kenya. Journal of Dairy Science, 2004. 87: p. 4145-4149.