Modeling, analysis and defense strategies against Internet attacks.

Third, we have analyzed the tradeoff between delay caused by filtering of worms at routers, and the delay due to worms' excessive amount of network traffic. We have used the optimal control problem, to determine the appropriate tradeoffs between these two delays for a given rate of a worm spreading. Using our technique we can minimize the overall network delay by finding the number of routers that should perform filtering and the time at which they should start the filtering process.Many early Internet protocols were designed without a fundamentally secure infrastructure and hence vulnerable to attacks such as denial of service (DoS) attacks and worms. DoS attacks attempt to consume the resources of a remote host or network, thereby denying or degrading service to legitimate users. Network forensics is an emerging area wherein the source or the cause of the attacker is determined using IDS tools. The problem of finding the source(s) of attack(s) is called the "trace back problem". Lately, Internet worms have become a major problem for the security of computer networks, causing considerable amount of resources and time to be spent recovering from the disruption of systems. In addition to breaking down victims, these worms create large amounts of unnecessary network data traffic that results in network congestion, thereby affecting the entire network.In this dissertation, first we solve the trace back problem more efficiently in terms of the number of routers needed to complete the track back. We provide an efficient algorithm to decompose a network into connected components and construct a terminal network. We show that for a terminal network with n routers, the trace back can be completed in O(log n) steps.Second, we apply two classical epidemic SIS and SIR models to study the spread of Internet Worm. The analytical models that we provide are useful in determining the rate of spread and time required to infect a majority of the nodes in the network. Our simulation results on large Internet like topologies show that in a fairly small amount of time, 80% of the network nodes is infected

Targeted anthelmintic treatment of parasitic gastroenteritis in first grazing season dairy calves using daily live weight gain as an indicator

Control of parasitic gastroenteritis in cattle is typically based on group treatments with anthelmintics, complemented by grazing management, where feasible. However, the almost inevitable evolution of resistance in parasitic nematodes to anthelmintics over time necessitates a reappraisal of their use in order to reduce selection pressure. One such approach is targeted selective treatment (TST), in which only individual animals that will most benefit are treated, rather than whole groups of at-risk cattle. This study was designed to assess the feasibility of implementing TST on three commercial farms, two of which were organic. A total of 104 first-grazing season (FGS), weaned dairy calves were enrolled in the study; each was weighed at monthly intervals from the start of the grazing season using scales or weigh-bands. At the same time dung and blood samples were collected in order to measure faecal egg counts (FEC) and plasma pepsinogen, respectively. A pre-determined threshhold weight gain of 0.75 kg/day was used to determine those animals that would be treated; the anthelmintic used was eprinomectin. No individual animal received more than one treatment during the grazing season and all treatments were given in July or August; five animals were not treated at all because their growth rates consistently exceeded the threshold. Mean daily live weight gain over the entire grazing season ranged between 0.69 and 0.82 kg/day on the three farms. Neither FEC nor pepsinogen values were significantly associated with live weight gain. Implementation of TST at farm level requires regular (monthly) handling of the animals and the use of weigh scales or tape, but can be integrated into farm management practices. This study has shown that acceptable growth rates can be achieved in FGS cattle with modest levels of treatment and correspondingly less exposure of their nematode populations to anthelmintics, which should mitigate selection pressure for resistance by increasing the size of the refugia in both hosts and pasture

National Fisheries Laboratory Category 2 parasite guide

This report provides a guide into Category 2 parasites affecting freshwater fish and salmonids. First a brief summary is given of distinctions between parasites of Category 1 and 2. The Guide then provides a list of category 2 parasites, highlighting damage they can cause, species of fish affected, if it can be treated, how widespread the parasite is and how it is transferred

Prevalence of Gastrointestinal Helminths in Thai Indigenous Chickens Raised Under Backyard Conditions in Northern Thailand

SUMMARY This study aimed to evaluate the prevalence and worm burden of gastrointestinal parasites in Thai indigenous chickens (Gallus gallus domesticus) kept under extensive backyard conditions in Northern Thailand. A total of 211 male (N = 98) and female (N = 113) chickens from 11 smallholder farms were selected randomly between December 2016 and May 2017. At slaughter, fecal samples were collected to estimate fecal egg counts (presented as eggs per gram of feces) and oocyst counts (oocyst per gram of feces). The gastrointestinal tract of each animal was examined for the presence of parasites. The percentage of FEC- and FOC-positive samples was 33.7 and 55.4%, respectively. On average, 111 ± 328 ascarid eggs and 2,983 ± 11,641 coccidian oocysts were found. From the post mortem examination, 3 nematode species and cestodes were recovered. A total of 156 (73.9%) of the sampled chickens were infected with at least 1 helminth species. Average worm burden per chicken was 46.7 (SD = 50.9, median = 30). The most prevalent species were the nematodes Heterakis gallinarum (70.6%) followed by Ascaridia galli (60.2%) and Capillaria spp. (44.1%). The overall prevalence of cestodes was 27.7%. Apart from A. galli with higher prevalence in males than in females (P ≤ 0.05), gender did neither affect prevalence nor worm burden (P > 0.05). Growth performance was not negatively affected by helminth infections. In conclusion, the vast majority of Thai native chickens are subclinically infected with at least 1 helminth species under the studied backyard conditions

Some aspects of the biology of Dactylogyrus vastator Nybelin, 1924 (Monogenea) a gill parasite of Cyprinus carpio L.

Dactylogyrus vastator Nybelin, 1924 is a common, economically significant pathogenic monogenean parasite of European carp, Cyprinus carpio L. D. vastator attaches to the gills by means of an attachment organ, the opisthaptor, which carries two large hamuli, a connecting bar and fourteen peripheral marginal hooks. Experiments during the present study have shown that populations of D. vastator on young carp reach peaks of abundance at 12°C, 19°C and 22°C within 5,3 to 4 and 6 weeks, respectively, followed by a decline to a lower level. Parasite abundance was greatest at 19°C and lowest at 12°C. Principal component analysis was used to investigate the effects of temperature on sclerite measurements. It was shown that the basic length and internal root length of the hamuli are the major factors by which populations of the parasite reared under different temperature regimes can be discriminated. Parasites reared at 12°C were clearly separated from those reared at 14°C and 19°C. Scanning and transmission electron microscopic studies were carried out on D. vastator. The outer layer of the epidermis is a syncytial structure. Circular and longitudinal muscle is found beneath this outer layer. The muscle bands are not of uniform thickness. Epidermal secreting cell bodies are located below the muscle layer and communicate with the outer layer via ducts or channels. Possible. epidermal sensillae are unequally distributed over the worm's body. The parasite has four cephalic lobes each of which is provided with a cup-like opening at the border; the unicellular cephalic gland cells empty their contents into a collecting duct. D. vastator shows protandous gonadial development. The female reproductive system has an oval shaped ovary, uterus, ootype, accessory glands, whereas the male reproductive system has a single lobed testis located in the posterior region of the body. Clean sclerites prepared by using an ultrasonication technique were examined under the electron microscope. The hamuli of adult and immature dactylogyrids are divided into internal and external processes and a shaft which ends in a spike. Marginal hooks have a blade and spike. The adult and immature worms can be differentiated by the structure of the auxiliary sclerite. In mature specimens the outer and the inner surfaces of the auxiliary sclerite remain separate. The surface of the hamuli has an interlocking array of striations. The two hamuli are of unequal size in both adult and immature worms. The parasites are not randomly distributed over the gill apparatus. There were no significant differences between gill arches but parasites aggregated in certain areas of the gills, in particular the ventral proximal secondary filaments on both sides of the hemibranch are favoured. Smaller D. vastator which are found in higher numbers on fish presumably represent worms which have recently invaded the host. Larger worms are found in lower numbers. This may be due to competition or an age related mortality in which mature worms die off. D. vastator does not need to be attached to the host tissue to initiate egg laying. In-vitro oviposition was observed and described, however the egg laying rate varies with the environmental temperature. The first eggs that are produced in-vitro are of a large size but as time continues the size of the eggs becomes smaller. A severe hyperplastic tissue response was observed two weeks after the start of an experiment where fish infected with D. vastator were mixed with naive fish. Damage to the host gills caused by D. vastator was observed. Hyperplasia of gill tissue led ultimately to fusion of the secondary lamellae. Affected fish became lethargic and gulped air at the surface. Challenge experiments were carried out to investigate whether there is an acquired immunity by carp to D. vastator infections. The challenged fish had a significantly lower parasite burden compared to the naive fish. The infection causes a change in the blood proteins, as was clearly shown by comparison of infected and uninfected fish, the former having very visibly separable additional bands using gel electrophoresis

Breeding for Resistance to Infectious Diseases in Small Ruminants

Livestock Production/Industries,

Mathematical Modelling of the Effects of Health Interventions on the Evolution of Life History in Disease-Causing Organisms

We use mathematical models to explore the evolutionary implications of health interventions affecting age-dependent mortality schedules in two contexts, antihelminthics targeting parasitic nematodes, and programs directed against malaria vectors. We show that interventions targeting parasitic nematodes can exert selection pressure to either shorten or extend the time to maturity, depending on the details of worm mortality functions with and without the intervention. Interventions may therefore generate selection favouring later-maturing, larger and more fecund worms, rather than inevitably favouring the evolution of smaller, less fecund and hence potentially clinically less damaging worms as previously assumed. The evolution of insecticide-resistant mosquitoes threatens conventional public health programs targeting malaria vectors. By exploiting the high mortality rates of wild mosquitoes and the delay between malaria infection and infectiousness in mosquito hosts, late-life-acting (LLA) insecticides which kill only older mosquitoes can in principle provide effective transmission control in combination with very low selection for resistance. We develop a novel mathematical model to evaluate the potential of such pesticides and find that theoretical LLAs which affect only mosquitoes above a specific age can offer transmission control comparable with conventional insecticides, combined with very low selection for resistance. Benefits are maximised by generating lower mortality in mosquitoes not infected with malaria, and contacting and killing mosquitoes prior to biting. We also explore the optimum virulence characteristics for a fungal LLA biopesticide, and find that it may offer improved transmission reduction as well as lower selection for resistance when compared to some insecticides in current use. Lastly we use our model to assess a candidate for development as a chemical LLA. Finally, we explore a disparity between our model results and the conventional wisdom that a rare, recessive resistance allele will not spread. We find that the assumption of discrete, non-overlapping generations is key in this context