Medicinal plants – prophylactic and therapeutic options for gastrointestinal and respiratory diseases in calves and piglets? A systematic review

Ayrle, Hannah; Mevissen, Meike; Kaske, Martin; Nathues, Heiko; Gruetzner, Niels; Melzig, Matthias; Walkenhorst, Michael

Based on this review, the most prominent plant species for stimulation of the immune system is Echinacea purpurea (L.) MOENCH. The main constituents are polysaccharides, alkylamides, caffeic acid esters and polyacetylenes [91] . It has been used in therapy for stimulation of the immune system in human medicine, mainly for prevention of viral infections of the respiratory tract [92] . A total of 23 clinical and in vivo studies revealed multiple effects on the innate and acquired immune system. Echinacea purpurea (L.) MOENCH was shown to increase the immune response towards swine erysipelas vaccination in piglets [93] , prevented enveloped virus infections in humans [94] and reduced symptom severity in naturally acquired upper respiratory tract infections in humans [95] . In contrast, seven clinical or in vivo studies reported the absence of the above mentioned effects. For example Echinacea purpurea (L.) MOENCH failed to enhance growth or to show any immunomodulatory effect in one study in pigs [96] . Reasons for these negative results may be due to a very small number of individuals, an improper dosage or study design. As mentioned above, the diversity of non-standardized Echinacea preparations with varying chemistry is likely to result in different findings. In some studies, the dosage was not reported, and therefore it was not possible to estimate how much plant material or drug equivalent was administered per day. Consequently, due to missing data final conclusions cannot be drawn. Nevertheless, eight in vivo studies reported modulations of immune system and blood cell count, and no studies were found disproving these effects. Different Echinacea species were found to increase the total number of white and red blood cells in mice [97] and horses [98] . Twenty-six in vitro studies demonstrated the underlying mechanisms of immunomodulatory effects of Echinacea purpurea (L.) MOENCH. It was reported to activate macrophages and natural killer cells [99] [100] [101] and to modulate several cytokines [102] [103] [104] [105] . Echinacea purpurea (L.) MOENCH is known as a safe immunostimulant in humans and several products are available on the market. No reported interactions with other drugs and no toxic effects after overdosage were reported [106] . Possible rare adverse effects such as hypersensitivity reactions are reported, but no adverse effects have been observed during longterm administration [107] . In general, Echinacea purpurea (L.) MOENCH seems to be effective in preventing respiratory diseases and as an early intervention immediately after onset of first symptoms of infectious diseases [95] . However, further veterinary clinical studies need to be performed, especially to evaluate effective dosages.