Evolution of complex life cycles in trophically transmitted helminths. I. Host incorporation and trophic ascent.

Links between parasites and food webs are evolutionarily ancient but dynamic: life history theory provides insights into helminth complex life cycle origins. Most adult helminths benefit by sexual reproduction in vertebrates, often high up food chains, but direct infection is commonly constrained by a trophic vacuum between free-living propagules and definitive hosts. Intermediate hosts fill this vacuum, facilitating transmission to definitive hosts. The central question concerns why sexual reproduction, and sometimes even larval growth, is suppressed in intermediate hosts, favouring growth arrest at larval maturity in intermediate hosts and reproductive suppression until transmission to definitive hosts? Increased longevity and higher growth in definitive hosts can generate selection for larger parasite body size and higher fecundity at sexual maturity. Life cycle length is increased by two evolutionary mechanisms, upward and downward incorporation, allowing simple (one-host) cycles to become complex (multihost). In downward incorporation, an intermediate host is added below the definitive host: models suggest that downward incorporation probably evolves only after ecological or evolutionary perturbations create a trophic vacuum. In upward incorporation, a new definitive host is added above the original definitive host, which subsequently becomes an intermediate host, again maintained by the trophic vacuum: theory suggests that this is plausible even under constant ecological/evolutionary conditions. The final cycle is similar irrespective of its origin (upward or downward). Insights about host incorporation are best gained by linking comparative phylogenetic analyses (describing evolutionary history) with evolutionary models (examining selective forces). Ascent of host trophic levels and evolution of optimal host taxa ranges are discussed.

Evolution of complex life cycles in trophically transmitted helminths. II. How do life-history stages adapt to their hosts?

We review how trophically transmitted helminths adapt to the special problems associated with successive hosts in complex cycles. In intermediate hosts, larvae typically show growth arrest at larval maturity (GALM). Theoretical models indicate that optimization of size at GALM requires larval mortality rate to increase with time between infection and GALM: low larval growth or paratenicity (no growth) arises from unfavourable growth and mortality rates in the intermediate host and low transmission rates to the definitive host. Reverse conditions favour high GALM size or continuous growth. Some support is found for these predictions. Intermediate host manipulation involves predation suppression (which decreases host vulnerability before the larva can establish in its next host) and predation enhancement (which increases host vulnerability after the larva can establish in its next host). Switches between suppression and enhancement suggest adaptive manipulation. Manipulation conflicts can occur between larvae of different ages/species a host individual. Larvae must usually develop to GALM before becoming infective to the next host, possibly due to trade-offs, e.g. between growth/survival in the present host and infection ability for the next host. In definitive hosts, if mortality rate is constant, optimal growth before switching to reproduction is set by the growth/morality rate ratio. Rarely, no growth occurs in definitive hosts, predicted (with empirical support) when larval size on infection exceeds growth/mortality rate. Tissue migration patterns and residence sites may be explained by variations in growth/mortality rates between host gut and soma, migration costs and benefits of releasing eggs in the gut.

Why do larval helminths avoid the gut of intermediate hosts?

In complex life cycles, larval helminths typically migrate from the gut to exploit the tissues of their intermediate hosts. Yet the definitive host's gut is overwhelmingly the most favoured site for adult helminths to release eggs. Vertebrate nematodes with one-host cycles commonly migrate to a site in the host away from the gut before returning to the gut for reproduction; those with complex cycles occupy sites exclusively in the intermediate host's tissues or body spaces, and may or may not show tissue migration before (typically) returning to the gut in the definitive host. We develop models to explain the patterns of exploitation of different host sites, and in particular why larval helminths avoid the intermediate host's gut, and adult helminths favour it. Our models include the survival costs of migration between sites, and maximise fitness (=expected lifetime number of eggs produced by a given helminth propagule) in seeking the optimal strategy (host gut versus host tissue exploitation) under different growth, mortality, transmission and reproductive rates in the gut and tissues (i.e. sites away from the gut). We consider the relative merits of the gut and tissues, and conclude that (i) growth rates are likely to be higher in the tissues, (ii) mortality rates possibly higher in the gut (despite the immunological inertness of the gut lumen), and (iii) that there are very high benefits to egg release in the gut. The models show that these growth and mortality relativities would account for the common life history pattern of avoidance of the intermediate host's gut because the tissues offer a higher growth rate/mortality rate ratio (discounted by the costs of migration), and make a number of testable predictions. Though nematode larvae in paratenic hosts usually migrate to the tissues, unlike larvae in intermediates, they sometimes remain in the gut, which is predicted since in paratenics mortality rate and migration costs alone determine the site to be exploited.

To grow or not to grow? Intermediate and paratenic hosts as helminth life cycle strategies.

Larval helminths in intermediate hosts often stop growing long before their growth is limited by host resources, and do not grow at all in paratenic hosts. We develop our model [Ball, M.A., Parker, G.A., Chubb, J.C., 2008. The evolution of complex life cycles when parasite mortality is size- or time-dependent. J. Theor. Biol. 253, 202-214] for optimal growth arrest at larval maturity (GALM) in trophically transmitted helminths. This model assumes that on entering an intermediate host, larval death rate initially has both time- (or size-) dependent and time-constant components, the former increasing as the larva grows. At GALM, mortality changes to a new and constant rate in which the size-dependent component is proportional to that immediately before GALM. Mortality then remains constant until death or transmission to the definitive host. We analyse linear increasing and accelerating forms for time-dependent mortality to deduce why there is sometimes growth (intermediate hosts) and sometimes no growth (paratenic hosts). Calling i the intermediate or paratenic host, and j the definitive host, conditions favouring paratenicity are: (i) high values in host i for size at establishment, size-related mortality, expected intensity, (ii) low values in host i for size-independent mortality rate, potential growth rate, transmission rate to j, and ratio of death rate in j/growth rate in j. Opposite conditions favour growth in the (intermediate) host, either to GALM or until death without GALM. We offer circumstantial evidence from the literature supporting some of these predictions. In certain conditions, two of the three possible growth strategies (no growth; growth to an optimal size then growth arrest (GALM); unlimited growth until larval death) can exist as local optima. The effect of the discontinuity in death rate after GALM is complex and depends on mortality and growth parameters in the two hosts, and on the mortality functions before and after GALM.

The evolution of complex life cycles when parasite mortality is size- or time-dependent.

In complex cycles, helminth larvae in their intermediate hosts typically grow to a fixed size. We define this cessation of growth before transmission to the next host as growth arrest at larval maturity (GALM). Where the larval parasite controls its own growth in the intermediate host, in order that growth eventually arrests, some form of size- or time-dependent increase in its death rate must apply. In contrast, the switch from growth to sexual reproduction in the definitive host can be regulated by constant (time-independent) mortality as in standard life history theory. We here develop a step-wise model for the evolution of complex helminth life cycles through trophic transmission, based on the approach of Parker et al. [2003a. Evolution of complex life cycles in helminth parasites. Nature London 425, 480-484], but which includes size- or time-dependent increase in mortality rate. We assume that the growing larval parasite has two components to its death rate: (i) a constant, size- or time-independent component, and (ii) a component that increases with size or time in the intermediate host. When growth stops at larval maturity, there is a discontinuous change in mortality to a constant (time-independent) rate. This model generates the same optimal size for the parasite larva at GALM in the intermediate host whether the evolutionary approach to the complex life cycle is by adding a new host above the original definitive host (upward incorporation), or below the original definitive host (downward incorporation). We discuss some unexplored problems for cases where complex life cycles evolve through trophic transmission.

Percutaneous absorption of methotrexate: effect on epidermal DNA synthesis in hairless mice.

One of the presumed reasons for the lack of clinical activity of topical methotrexate in psoriasis is insufficient percutaneous penetration necessary to inhibit epidermal DNA synthesis. The present study was undertaken to select a vehicle to optimize penetration of methotrexate in vitro and to determine the effects of this topical formulation on epidermal DNA synthesis in vivo in hairless mouse skin. Increased penetration of methotrexate was obtained in human skin in vitro with Vehicle N compared to water and n-decylmethylsulfoxide vehicles. Repeated topical application of this methotrexate/Vehicle N preparation produced marked epidermal atrophy in treated sites in both normal and hyperproliferative essential fatty acid deficient hairless mouse skin without similar effects at a distant skin site. Local inhibition of epidermal DNA synthesis was also obtained without systemic effects at a distant site. These studies demonstrate that methotrexate in Vehicle N may produce a direct effect on epidermis which may be useful for the topical therapy of psoriasis.

Sperm competition games: a prospective analysis of risk assessment.

We develop the logic of assessment of sperm competition risk by individual males where the mechanism of sperm competition follows a 'loaded raffle' (first and second inseminates of a female have unequal prospects). Male roles (first or second to mate) are determined randomly. In model 1, males have no information about the risk associated with individual females and ejaculation strategy depends only on the probability, q, that females mate twice. Evolutionarily stable strategy (ESS) ejaculate expenditure increases linearly from zero with q, and reduces with increasing inequality between ejaculates, though the direction of the loading (which role is favoured) is unimportant. In model 2, males have perfect information and can identify each of three risk states: females that will (1) mate just once ('no risk'), (2) mate twice but have not yet mated ('future risk'), and (3) mate twice and have already mated ('past risk'). The ESS is to ejaculate minimally with 'no risk' females, and to expand equally with 'past' and 'future' risk females; the direction of the competitive loading is again unimportant. Expenditure again increases with risk, but is now non-zero at extremely low risk. Model 3 examines three cases of partial information where males can identify only one of the three risk states and cannot distinguish between the other two: they therefore have just two information sets or 'contexts'. Expenditure in both contexts typically rises non-linearly from zero with q, but (whatever the loading direction) expenditure is higher in the context with higher risk (e.g. if contexts are 'mated' and 'virgin', males spend more with mated females). However, in highly loaded raffles, sperm expenditure can decrease over part of the range of risk. Also, the direction of the loading now affects expenditure. Biological evidence for the predictions of the models is summarized and discussed.

Surgical treatment of subchondral cyst-like lesions in the tibia of an adult pony.

A 13 year-old pony was evaluated because of right hind limb lameness of acute onset. Radiographs of the right tarsus obtained shortly after the onset of lameness were normal, but results of nuclear scintigraphy were abnormal. Two radiolucent subchondral cyst-like lesions of the distal part of the tibia were seen on radiographs obtained 9 months later. The lesions were surgically decompressed, and the pony was sound 1 year later. It is hypothesized that a traumatic insult created a crack or split in the articular cartilage that allowed subsequent development of the cyst-like lesions.

Evaluation of itraconazole-dimethyl sulfoxide ointment for treatment of keratomycosis in nine horses.

OBJECTIVE: To evaluate the efficacy of itraconazole-dimethyl sulfoxide ointment for treatment of keratomycosis in horses in the northeastern United States. DESIGN: Prospective clinical trial. ANIMALS: 9 horses (10 affected eyes). PROCEDURE: All horses treated for keratomycosis at Cornell University between July 1994 and July 1996 were included in the study. The diagnosis of keratomycosis was confirmed by cytologic examination, and all horses were treated with 0.25 ml of a 1% itraconazole-30% dimethyl sulfoxide petrolatum-based ointment, applied to the affected eye every 4 hours. RESULTS: Topical application of itraconazole-dimethyl sulfoxide ointment (q 4 h) resolved keratomycosis in 8 of 10 eyes; mean duration of treatment was 34.6 days (range, 16 to 53 days). CLINICAL IMPLICATIONS: Results of this study indicate topical administration of itraconazole-dimethyl sulfoxide ointment may provide an additional treatment option for horses with keratomycosis.

Clinical appearances, healing patterns, risk factors, and outcomes of horses with fungal keratitis: 53 cases (1978-1996)

OBJECTIVE: To compare initial clinical appearances, healing mechanisms, risk factors, and outcomes of horses with fungal keratitis. DESIGN: Retrospective analysis. ANIMALS: 52 horses (53 eyes) with fungal keratitis. PROCEDURE: Medical records and clinical photographs of eyes were reviewed. Keratomycoses were categorized on the basis of clinical appearance at initial examination and pattern of healing. RESULTS: Five distinct forms of mycotic keratitis were recognized. Of 53 affected eyes, 34 (64%) retained sight and had varying degrees of corneal scarring after treatment, 6 (11%) had a cosmetic appearance but were blind, and 13 (25%) were enucleated. Bacterial-like ulcers were the most frequent type and the most difficult for predicting outcome. Eyes affected by superficial fungal keratitis were likely to be chronically infected and to require debridement and extended treatment but usually healed with minimal scarring. Keratomycosis with a surrounding furrow resulted in a grave prognosis. Aspergillus organisms were isolated from 9 of 10 such eyes. Cake-frosting material was a positive prognostic sign. Fungal corneal stromal abscesses tended to be caused by yeast. CLINICAL IMPLICATIONS: This information will aid practitioners in recognizing various forms of fungal keratitis and guide them when making therapeutic decisions and prognoses for affected horses.

Sperm competition games: the risk model can generate higher sperm allocation to virgin females.

We examine the risk model in sperm competition games for cases where female fertility increases significantly with sperm numbers (sperm limitation). Without sperm competition, sperm allocation increases with sperm limitation. We define 'average risk' as the probability q that females in the population mate twice, and 'perceived risk' as the information males gain about the sperm competition probability with individual females. If males obtain no information from individual females, sperm numbers increase with q unless sperm limitation is high and one of the two competing ejaculates is strongly disfavoured. If males can distinguish between virgin and mated females, greater sperm allocation to virgins is favoured by high sperm limitation, high q, and by the second male's ejaculate being disfavoured. With high sperm limitation, sperm allocation to virgins increases and to mated females decreases with q at high q levels. With perfect information about female mating pattern, sperm allocation (i) to virgins that will mate again exceeds that to mated females and to virgins that will mate only once, (ii) to virgins that mate only once exceeds that for mated females if q is high and there is high second male disadvantage and (iii) to each type of female can decrease with q if sperm limitation is high, although the average allocation increases at least across low q levels. In general, higher sperm allocation to virgins is favoured by: strong disadvantage to the second ejaculate, high sperm limitation, high average risk and increased information (perceived risk). These conditions may apply in a few species, especially spiders.

Sperm competition, mating rate and the evolution of testis and ejaculate sizes: a population model.

There are various ways to estimate ejaculate expenditure. Ejaculate size or sperm number (s) is an absolute number of units of ejaculate. Relative ejaculate expenditure (E) is the expenditure on the ejaculate as the proportion of the total expenditure on all aspects of the mating, including finding and acquiring a female, and so on. Relative testis size or gonadosomatic index (sigma) is testes mass divided by body mass; it is assumed to reflect the product of mating rate (M) and ejaculate mass (s). In a new model, where mating rate, sperm competition and sperm allocation interact, and where the female's inter-clutch interval is assumed to be independent of s or M, we show that sigma is directly proportional to the mean E for a species; across species sigma and E increase monotonically with sperm competition. However, the relation between s and sperm competition across species depends on the range of sperm competition (low risk or high intensity): s increases with sperm competition at low risk levels, but decreases with sperm competition at high intensity levels. This situation arises because s alpha E/M; both E and M increase with sperm competition, but E increases differently with sperm competition in its two ranges.

Vegetative endocarditis in an Appaloosa gelding.

A 5-year-old Appaloosa gelding was presented with a history of intermittent multiple joint swelling, weight loss, and anemia. Physical examination and clinical pathology revealed a grade IV/VI holodiastolic murmur, louder on the left, and a marked hyperproteinemia. Echocardiography of the heart demonstrated a large vegetative lesion on one of the aortic valve cusps. Blood cultures did not elucidate the causative organism, and the disease was refractory to empiric antibiotic therapy. The horse was euthanized after approximately 2 months of therapy.

Sperm competition games: inter- and intra-species results of a continuous external fertilization model.

We investigate the relationship between sperm competition intensity and sperm expenditure, both across species and within a species, using a two sperm competition models. In model 1, the males cannot assess the number of competitors, and their ejaculate effort is shaped by the average number of competitors. In model 2, males can assess the number Ni of competitors at each spawning exactly. Males can vary the mass m of their sperm and the number si at a spawning. The aim is to find the evolutionarily stable strategies and hence the way that m and si vary with Ni. A continuous fertilization model in which the sperm have to swim in order to fertilize an egg is described. This is used to find simultaneous equations describing m and si. These are solved numerically.

Sperm competition games: a general approach to risk assessment.

We investigate game theory models of ejaculate expenditure by males in a species where there is a risk probability, q, that females will mate twice before laying a given set of eggs. With frequency 1-q females mate just once; then males optimally ejaculate an arbitrary minimum amount of sperm. The paper extends the analysis of Parker et al. (1997) in which males have limited information about the three risk states of the female: 0 (virgins which will mate now but not again), 1 (virgins which will mate now and then once more), and 2 (once-mated females who will mate now but not again). We derive a general structure for finding ESSs under imperfect information about states, and examine two special cases in which males know the overall risk probability q, but have imperfect knowledge of the states (0, 1, 2). In Case 1, males cannot distinguish between states 0 and 1 but have limited information about state 2. As their information increases, so does the difference in sperm allocation, with more going to females assessed as mated (state 2) than to females assessed as virgins (0, 1). This difference decreases with q in a species, but the average ejaculate expenditure increases with q. Even for small amounts of information, the behaviour as q-->0 is different from that predicted for zero information. In Case 2, males have perfect information about state 2, but limited information about states 0, 1. This has a major effect if q is small: males effectively behave as if they had perfect information by giving equal amounts of sperm to females assessed as 1 as those assessed to be 2, while giving a minimum amount to females assessed as 0. Ejaculate expenditures generally increase with the overall species-level risk q. A result common to both cases is that even a small amount of information allows more strategic choice than the zero information case and hence qualitatively different behaviour.

Sperm competition games: external fertilization and "adaptive"' infertility.

We develop a model of a continuous fertilization process in which eggs and sperm are shed simultaneously, and in which the eggs are fertilized at a rate proportional to sperm density surrounding the egg mass. The model derives the ESS size and number of sperm in an ejaculate of an externally-fertilizing animal such as a fish species, in which the probability or intensity of sperm competition varies. It also predicts the ESS level of infertility (eggs remaining unfertilized after all sperm have died). Sperm size is assumed to increase sperm competitive ability (e.g. by increasing speed) and is also assumed to affect sperm longevity (either positively or negatively). Ejaculate expenditure is traded off against expenditure on obtaining further spawnings, and size and number of sperm can vary independently. The model predicts that the ESS ejaculate expenditure (product of sperm size and number) should increase, and that the ESS infertility should decrease with sperm competition intensity measured across species. Other results depend on the way that sperm size affects longevity. The available biological evidence suggests that longevity decreases with sperm size, probably because the main increase is in tail length which increases sperm energy expenditure. In this case, sperm size should increase with sperm competition intensity from an optimum at zero competition which maximizes the total distance travelled by the entire ejaculate in its lifetime, to an optimum for maximum sperm competition which maximizes the product of speed and sperm number. However, if longevity increases with sperm size, then the non-competitive optimal sperm size is greater than that for maximum competition, so that sperm size decreases with sperm competition intensity. Sperm numbers typically increase with sperm competition intensity, and always so if sperm competition is high enough, though decreases are possible over a range of low sperm competition intensity if (i) sperm longevity decreases with sperm size, and (ii) infertility is high enough.

Sperm competition games: a comparison of loaded raffle models and their biological implications.

Our main aim is to compare the additive model, due to Mesterton-Gibbons, and the multiplicative model, due to Parker, of sperm allocation under sperm competition, when other influences are treated in the same way. We first review these (and other) models and their foundations, leading to a generalization of the multiplicative model. Sperm is assumed to cost energy, and this constraint is incorporated differently in the two models. These give the same results in the random-roles situation when the males occupy roles (of first and second to mate) randomly: the number of sperm ejaculated in the favoured role is greater than that in the disfavoured role by an amount that depends on the effect of sperm limitation (i.e. the probability that there is insufficient sperm to ensure full fertility). If the latter is negligible, or the fertilization raffle fair, this difference is zero, as Parker found originally. In the constant roles situation (where males of a particular type always occupy the same role) the predictions differ: the additive model has the same predictions as in the random roles case, but the multiplicative model predicts that males of the type occupying the favoured role ejaculate less than males of the type occupying the disfavoured role, in accord with Parker's original conclusion. The fitnesses of the two types of male can be calculated in the multiplicative model: the fitness of the favoured male is usually higher, even if he has to expend more energy in "finding" a female, e.g. through fighting, etc. These conclusions relate to inter-male behaviour (i.e. of different male types), as distinct from intra-male behaviour (i.e. of a given male when in different roles). We analyse situations in which one male type has some probability of acting in its less usual role: calculations with varying amounts of sperm limitation are presented. It is found that the presence of a male of a different type has an effect on intra-male ejaculate behaviour, which also depends critically on the role usually occupied. We conclude that the multiplicative model is the more accurate model and provides more information. Some experimental data on sperm numbers are used to find the effects of sperm limitation. For species which conform to the loaded raffle model, sperm limitation typically has small or negligible effects: in this case, we argue that empiricists should look for equal ejaculates in the two roles when studying random role situations; when roles are occupied non-randomly average sperm expenditure should be greater by male types typically occupying the disfavoured role, but within a male type, expenditure should be greater in the role it typically occupies.

Sperm competition games: sperm selection by females.

We analyse a co-evolutionary sexual conflict game, in which males compete for fertilizations (sperm competition) and females operate sperm selection against unfavourable ejaculates (cryptic female choice). For simplicity, each female mates with two males per reproductive event, and the competing ejaculates are of two types, favourable (having high viability or success) or unfavourable (where progeny are less successful). Over evolutionary time, females can increase their level of sperm selection (measured as the proportion of unfavourable sperm eliminated) by paying a fecundity cost. Males can regulate sperm allocations depending on whether they will be favoured or disfavoured, but increasing sperm allocation reduces their mating rate. The resolution of this game depends on whether males are equal, or unequal. Males could be equal: each is favoured with probability, p, reflecting the proportion of females in the population that favour his ejaculate (the 'random-roles' model); different males are favoured by different sets of females. Alternatively, males could be unequal: given males are perceived consistently by all females as two distinct types, favoured and disfavoured, where p is now the frequency of the favoured male type in the population (the 'constant-types' model). In both cases, the evolutionarily stable strategy (ESS) is for females initially to increase sperm selection from zero as the viability of offspring from unfavourable ejaculates falls below that of favourable ejaculates. But in the random-roles model, sperm selection decreases again towards zero as the unfavourable ejaculates become disastrous (i.e. as their progeny viability decreases towards zero). This occurs because males avoid expenditure in unfavourable matings, to conserve sperm for matings in the favoured role where their offspring have high viability, thus allowing females to relax sperm selection. If sperm selection is costly to females, ESS sperm selection is high across a region of intermediate viabilities. If it is uncostly, there is no ESS in this region unless sperm limitation (i.e. some eggs fail to be fertilized because sperm numbers are too low) is included into the model. In the constant-types model, no relaxation of sperm selection occurs at very low viabilities of disfavoured male progeny. If sperm selection is sufficiently costly, ESS sperm selection increases as progeny viability decreases down towards zero; but if it is uncostly, there is no ESS at the lowest viabilities, and unlike the random-roles model, this cannot be stabilized by including sperm limitation. Sperm allocations in the ESS regions differ between the two models. With random roles, males always allocate more sperm in the favoured role. With constant types, the male type that is favoured allocates less sperm than the disfavoured type. These results suggests that empiricists studying cryptic female choice and sperm allocation patterns need to determine whether sperm selection is applied differently, or consistently, on given males by different females in the same population.

Corneal concentrations and preliminary toxicological evaluation of an itraconazole/dimethyl sulphoxide ophthalmic ointment.

The objectives of this study were to determine the concentration of itraconazole achieved in corneal tissue and aqueous humour after topical application of a 1% itraconazole ointment: to determine the effect of including dimethyl sulphoxide (DMSO) in the ointment on achievable ocular tissue itraconazole concentrations; and to assess if any gross or histopathologic ocular toxicity results from the topical application of 1% itraconazole with or without the addition of DMSO. The experimental trial consisted of 6 horses considered to have normal eyes. Each horse had one eye treated with 0.3 mL of 1% ultra-micronized itraconazole ointment and the fellow eye with 0.3 mL of 1% itraconazole/ 30% DMSO ointment. The ointment was applied every 6 h for a total of 28 treatments. Both ointments were well tolerated and no gross or histopathologic abnormalities developed during the trial. Corneal tissue and aqueous humour concentrations of itraconazole were determined using high performance liquid chromatography. Corneal tissue concentration averaged 1.1 (+/- 0.4) micrograms/g in horses treated with the 1% ultramicronized itraconazole ointment and 7.9 (+/- 3.3) micrograms/g for those treated with the 1% itraconazole/30% DMSO ointment: there was a statistically significant difference between ointments (P = 0.005) No itraconazole could be detected in the aqueous humour in either treatment group.

The antiviral effect of keishi-ni-eppi-ichi-to, a traditional Chinese herbal medicine, on influenza A2(H2N2) virus infection in mice.

The antiviral effect of Keishi-ni-eppi-ichi-to (TJS-064), a traditional Chinese herbal medicine, was investigated in mice infected with influenza A2(H2N2) virus. When mice exposed to a 5 LD50 dose of the virus were treated orally with a 70 mg/kg dose of TJS-064 1 day before and 1 day and 4 days after the infection, 100% survived over a 25-day experimental period. At the end of this period all the control mice, treated with saline alone, had died; their mean survival time in days (MSD) was 11.2 days. When mice infected with a 10 LD50 dose of the virus were treated with TJS-064, the MSD was > 17.4 days and there was a 50% survival rate, while the control group had a MSD of 8.7 days and a 0% survival rate. No significant antiviral effect of TJS-064 was observed when the agent was administered orally to mice infected with a 100 LD50 or larger dose of influenza virus. Pulmonary consolidations, virus titers in lung tissues and HAI titers in sera of infected mice treated with TJS-064 were all significantly lower than those of infected mice treated with saline. Interferon activities were detected in sera of mice treated with the agent at a dose of 100 mg/kg orally. Since viricidal and viristatic activities of the agent against influenza virus were not demonstrated, the antiviral effects of TJS-064 may be expressed through the host's antiviral functions including interferon production.